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Splitting stars – for us and for you!

We are experienced amateur astronomers who especially enjoy viewing double stars with long-focus refractors.  This journal is a record of our observations, but we also hope it will serve as a guide to you to help you plan observing sessions and choose double stars you want to observe.  In the column to the left you’ll find a drop down menu listing the doubles in this blog by constellation – and to the right there’s a list of our 10 most recent observations. Finally, you have two other choices:

  • First, you can read  our observations of a double and leave your own observations of that same star as a comment.
  • Second, you can subscribe to this blog so that you get email notifications when we add a star to it. Just check out the links in the right-hand column.

We’d love to hear from you regarding your own observations of the same doubles.

STT Objects in Lacerta, Part 1: OΣ 475, OΣ 477, and OΣ 479

It’s rather ironic that I find myself back in Lacerta once again, which is the scene of the last post I wrote here several months ago. But this is an intriguing little constellation, dim though it is, and is well worth spending some time here. This time we’ll concentrate on six of Otto Wilhem von Struve’s more challenging discoveries. The challenge here isn’t feeble starlight (with one exception) as much as the more dreaded difference in magnitudes. Fortunately the stingiest separation is 10.7”, so we have a fighting chance to separate these pairs. You’ll need a minimum of six inches of unobstructed aperture to resolve these stars, although given very dark skies, great transparency, and stable seeing (in other words, rather rare atmospheric cooperation), you might get by with five inches.

As historical background, Otto Struve published the first catalog of his discoveries in 1843 with a lengthy title which was typical of the era, Catalogue de 514 Étoiles Doubles et Multiples Découvertes Sur L’Hémisphère Céleste Boréal par La Grand Lunette de L’Observatoire Central de Poulkova. Fortunately, the title which has come into common usage is The Pulkova (or Pulkovo) Catalog. This particular survey of double stars was actually started on August 26th, 1841, by Otto’s father, Friedrich Wilhelm Struve, who turned it over to his son within a month. There were several additions and modifications to this catalog over the next decades, which resulted in the printing of subsequent editions, including a supplement of much wider pairs. Also lending a hand and providing many of the measures of these pairs was Johann Heinrich Mädler.

Let’s start by getting situated in Lacerta, which lies in the dim region between Cepheus and Cygnus. Even though the area is sparse in regard to eye-catching magnitudes, the north end of Lacerta lies in a star strewn stream of the Milky Way as it meanders through Cygnus, Cepheus, and Cassiopeia.

Stellarium screen image with labels added, click to enlarge.

Stellarium screen image with labels added, click to enlarge.

Note the directions indicated in the top left hand corner of this chart. Astronomical west is always the direction in which the constellations are rotating, which explains why it’s pointing in the direction shown. This is a depiction of the scene in late August or early September, when the constellations are slowly rotating toward the top of the chart.

You can also draw a line from Delta (δ) Cygni (just out of sight at the upper right of the chart) through Deneb, which will just miss the southern edge of 8 Lacerate. (Stellarium screen image with labels added, click to enlarge).

Stellarium screen image with labels added, click to enlarge.

If you’re having trouble pinning down the Lacertan Lizard, notice that a line drawn from Beta Cephei through Delta Cephei will take you right through the center of the distinctive Lacertan parallelogram. Also, a line drawn from Delta Cygni (out of view at the upper right hand corner) through Deneb will take you to the southern tip of Lacerata.

Our first stop is OΣ 477, which lies a couple of degrees north of 11 Lacertae:

Stellarium screen image with labels added, click for a better view.

Stellarium screen image with labels added, click for a better view.

If you look closely at the chart above, 4.46 magnitude 11 Lacertae forms a triangle with 6.38 magnitude HIP 111753 and 6.55 magnitude HIP 111428. OΣ 477 stands out distinctively just half a degree west of HIP 111428.

OΣ 477 (STT 477)     No HIP Number    SAO: 52303
RA: 22h 43.5m   Dec: 46° 02’
Magnitudes  AB: 7.43, 12.20   AC: 7.43, 11.24   CD: 11.24, 12.70
Separation   AB: 22.50”          AC: 182.70”         CD: 10.40”
Position Angle  AB: 262° (WDS 2015)  AC: 344° (WDS 2002)  CD: 127° (WDS 2015)
Distance: 256 Light Years (GAIA)
Spectral Classification:  A is F6

As I mentioned above, you need six inches of unobstructed aperture to spy the dim companions featured in this series. So you have to look closely to see the twelfth magnitude B companion, as well as distinguishing the difficult CD pair. Clicking on the sketch will enlarge it and make things much easier. (East and west reversed to match the refractor image).

As I mentioned above, you need six inches of unobstructed aperture to spy the dim companions featured in this series. So you have to look closely to see the twelfth magnitude B companion, as well as distinguishing the difficult CD pair. Clicking on the sketch will enlarge it and make things much easier. (North and south reversed to match the refractor image).

This was my third visit to this multiple star, and each time was an improvement over the time before. My first visit was on 8-21-2015, during which eleventh magnitude C was the only component I could catch. I came back a couple of weeks later (9-7-2015) and that time, with a determined application of averted vision, I pried 12.2 magnitude B out of the primarial glare, but still couldn’t distinguish 12.7 magnitude D clinging to C. My most recent visit, almost exactly a year after the second, was under much improved seeing conditions. Not only was B much easier to see, but D was also obvious when I looked closely. In fact all three components were such a breeze that I was surprised to see how difficult they had been when I looked at my notes from the prior visits.

Not only were the three components more cooperative, but I also picked out the faint star which is shown just to the left of B in the sketch, which was totally absent during the earlier encounters with OΣ 477. That star is identified in Aladin as UCAC4 681-126049 with a visual magnitude of 13.073. Combining the J and K magnitudes for it results in a similar magnitude of 13.021, so it’s safe to call it a 13.0 magnitude star. Again, it’s amazing the difference a cooperative atmosphere can make – sort of what you might call the difference between night and day.

By the way, a comparison of various UCAC4 and NOMAD-1 magnitudes for B, C, and D all resulted in remarkable consistency, each coming in within a few tenths of a magnitude of the WDS values, so all of the magnitudes shown in the data line above are very reliable.

Getting back to 13.0 magnitude UCAC4 681-126049, you might wonder why Otto Struve ignored that one at the time he observed B. There’s an easy answer to that question. When his father, F.G.W. Struve, started this survey of double stars, he established specific criteria, among which was a separation limit of 16” for companions fainter than ninth magnitude (p.16 of this source). Aladin shows a separation of 36.28” between UCAC4 681-126049 and the OΣ 477 primary, so that explains that. Otto Struve later added a supplement to the Pulkovo Catalog for wider pairs, but he apparently didn’t come back to this one. (The stars in that supplement were assigned a prefix of OΣΣ, which in WDS jargon has been transformed to STTA).

Of course that raises questions immediately with regard to the B and CD components since they’re well outside the 16” limit. With regard to the CD pair, the answer is pretty straight-forward: it was added in 1880, most likely by S.W. Burnham, although I haven’t been able to pin that down definitively. As for B, the answer is A – which is a cryptic way of saying that A has a lot of proper motion. In fact, that can be illustrated by the separation of the AB pair at the time of discovery in 1846, when it was a much tighter 9.6” (with a considerably different PA of 123 degrees). The most recent data, which comes from the GAIA catalog, shows the A component with a proper motion of +185 -009 (.185”/yr east and .009”/yr south), which means it’s moving eastward at a pretty good pace. The effect of that motion is easy to illustrate by using the Epoch tool slider in Aladin to compare and contrast the relative positions of the AB pair in 1846 and 2016:

Aladin image with labels added, click to enlarge.

Aladin image with labels added, click to enlarge.

Notice the red circles represent the positions of the two stars at the two dates shown. More proof that the heavens change just like everything else, albeit at a snail’s pace. Also, the separation between A and UCAC4 681-126049 in 1846 was 43”, which again illustrates why it wasn’t included in 1846 when Otto Struve measured the AB pair.

Now that we have that covered, we’ll move on to OΣ 479, also known as STT 479, AKA HN 42, AKA 13 Lacertae. Starting again at 11 Lacertae, you’ll find OΣ 479 is located 2 ½ degrees to the southeast. It and 11 Lacertae form a triangle with 4.95 magnitude 15 Lacertae. (Here’s our previous chart again).

OΣ 479 (STT 479) (HN 42) (13 Lacertae)
HIP: 112242    SAO: 52317
RA: 22h 44.1m   Dec: 41° 49’
Magnitudes: 5.21, 10.9
Separation:  14.4”
Position Angle: 130°
Distance: 256.5 Light Years (Simbad)
Spectral Classification:  A is G8 (WDS)

Again, you have to look closely to see the secondary, which is a bit more difficult than the secondary in the previous sketch. (East and west reversed to match the refractor image, click for a better view).

Again, you have to look closely to see the secondary, which is a bit more difficult than the secondary in the previous sketch. (North and south reversed to match the refractor image, click for a better view).

I had very little difficulty with this pair on the night I made the sketch above at 201x, which wasn’t the case a year earlier when I looked at it. On that night the secondary was immediately visible at 84x, but it decided to become difficult when I increased the magnification. At 152x, it vanished into the primarial glare, and then reappeared sporadically when I dropped back to 127x. It was more cooperative at 109x, but still a bit elusive, so I went back to 84x and was able to see it most of the time with direct vision, at other times only with averted vision.

There’s a huge difference in magnitude between the two stars, somewhat comparable to seeing the secondary of Polaris in a 50mm refractor. That pair has a Delta_M of 7.06 (magnitudes of 2.04 and 9.1) vs. 5.69 for this pair, which is fainter, so the comparison is not quite exact, but it will give you an idea of what to expect. However, I estimated the secondary to be at least a full magnitude fainter based on comparison with two nearby stars, which sheds some light on the comparison with Polaris. B appeared to me to be slightly fainter than UCAC4 659-108762 (which has a UCAC4 Vmag of 11.640) and slightly brighter than UCAC4 660-110091 (with a Vmag of 12.818), so the actual magnitude most likely lies somewhere in between.

William Herschel appears to have been the first to come across this pair of stars, having looked at them on October 17th, 1786. However he didn’t publish that observation until 1822, assigning a catalog number of H N 42 to it. His remarks on the pair were rather brief: “13 Lacertae has an extremely small star following, 3d class.” (p.171 of 1822 catalog). John Herschel also looked at 13 Lacertae in 1828, providing an estimated separation of 12” with a PA of 132.9 degrees. The first actual measure of the pair was made by Otto Struve in 1849. He recorded a separation of 14.57” and a position angle of 129.2 degrees. John Herschel recorded another measure of the pair that same year, turning in a separation of 14.70” and 129.1 degrees. Comparing those 1849 measures to the most recent 2012 WDS data shows very little change over the past 167 years.

On to our last star now. We’ll head south from OΣ 479 (with a bit of a tilt to the west) for a distance of 1° 40’ to 5.82 magnitude 12 Lacertae, then continue in the same direction another 1° 15’ to 4.89 magnitude 10 Lacertae, and then angle southeast for a distance of 1° 28’ to 6.03 magnitude HIP 111869. You’ll see OΣ 475 at the western corner of a triangle it forms with HIP 111869 and 6.65 magnitude HIP 111864. (The previous chart once more).

OΣ 475 (STT 475)     HIP: 111828   SAO: 72569
RA: 22h 39.1m   Dec: 37° 23’
Magnitudes  Aa, Ab: 6.83, 10.52   AB: 6.84, 10.80
Separation   Aa, Ab: 0.60”            AB: 16.10”
Position Angle  Aa, Ab: 50° (WDS 2009)    AB: 73°  (WDS 2008)
Distance: Unknown  (negative parallax)
Spectral Classification:   A is B2
Note: Aa, Ab is HDS 3216, AB is STT 475

And again you have to look closely to see the B component of this pair (it’s hiding in the glow of the primary between the four and five o’clock position). Notice both HIP 111869 and HIP 111864, which we used to locate OΣ 475, are in the field of view with it. (East & west reversed once again, click for a much better view).

And again you have to look closely to see the B component of this pair (it’s hiding in the glow of the primary between the four and five o’clock position). Notice both HIP 111869 and HIP 111864, which we used to locate OΣ 475, are in the field of view with it. (North and south reversed once again, click for a much better view).

I had little problem with the secondary during my two year-apart-observations since it popped into view immediately at 84x both times. I estimated it to be very similar in magnitude to UCAC4 638-120691 (located 9’ northwest), which has a Vmag of 11.008, so it appears the WDS magnitude of 10.8 is about right. Otto Struve first measured this pair in 1847 at 15.53” with a position angle of 72.8 degrees. John Herschel showed up here as well that same year, turning in a separation of 15.66” and a PA of 73.6”.

As for the Aa, Ab pair, good luck. A separation of .60” wouldn’t be out of reach for a large aperture dobsonian –- except for that annoying 3.69 magnitude difference between the two components. The HDS prefix refers to the Hipparcos Double Star survey, which first detected it in 1991. With a total of four observations recorded in the WDS, you can at least rest assured the secondary is really there if you launch a search for it.

Also hovering in the southwest quadrant of the field of view is an evenly illuminated pair, AG 284 (WDS 22387+3718), which has magnitudes of 9.86 and 9.94, separated by 26.3” with a PA of 230 degrees (WDS 2008 data). Your double-starred vision should have no problem latching onto those two.

That’s it for the first half of this tour – stay tuned for the second half coming up soon. Clear Skies!😎

Difficult Double Stars of the STT Variety

Back in the golden era of the late nineteenth and early twentieth centuries, when astronomy began to grow rapidly in the United States and Europe, communication with other astronomers was a slow process — especially when it took place between continents. For example, S.W. Burnham (1838-1921) sent many of his first double star discoveries of the early 1870’s to Milan, Italy, where Baron Ercole Dembowski (1812-1881) then made the first measures of those stars and mailed them back to Burnham in Chicago — a cycle which frequently took most of a year and sometimes longer. Burnham also actively published in European journals, primarily Germany’s Astronomische Nachrichten and England’s MNRAS (Monthly Notices of the Royal Astronomical Society), as did other American astronomers. Many a list of observations or manuscripts were dropped into the mail accompanied by doubt as to when, or if, it would reach its destination. Patience and confidence were virtues that came with experience, some of it no doubt learned with difficulty.

Communication between continents in this day and age is of course much faster, although publication cycles haven’t changed all that much – a paper or article sent to a publication frequently takes six months or longer to see the light of day. But the era of the internet and email creates possibilities that astronomers of Burnham and Dembowski’s day never would have dared to contemplate.

I’ve spent most of the last year putting those tools to good use, which has resulted in numerous publications in the Journal of Double Star Observers (JDSO), the vast majority of which have been in collaboration with Dr. Wilfried Knapp of Vienna, Austria. Most of those publications concern the more challenging of the double stars discovered by Otto Wilhelm Struve, which is why the articles are all titled “STT Double Stars with Large Delta_M.”

Now it’s a basic fact of life that when you push yourself beyond your comfort zone, you learn and grow in ways you never anticipated. Put more concisely, if you don’t try, you’ll never know. That applies to observational astronomy as well – in fact, especially to observational astronomy. When I first cast eyes on the list of double stars to be examined for the STT project, my initial thought was most of the faint secondaries on the list were too difficult to separate from their much brighter primaries. The astronomical term which describes that challenging difference in magnitudes between the two stars is “delta_M (or Δ_M)”, and thus the title of the papers.

Reams of material has been published about the relation between magnitude differentials (delta_M) and aperture, and numerous attempts have been made to pin down more precisely what can be detected and what can’t with specific apertures and magnitude differences. Although they’re certainly well intended, I’ve never been a big fan of those efforts, primarily because there are so many variables involved. The ability and experience of the observer, the quality of the optics, the telescope type, atmospheric conditions, altitude – all of those factors play a role that can’t be easily converted to numbers. But there’s one variable which is frequently overlooked: the accuracy of the published magnitudes.

I suspect that last one may catch many observers by surprise. But the reality is that magnitudes don’t get near the attention in double star catalogs as do separations and position angles. In fact, it’s not at all unusual in the case of the older double star discoveries, such as those of Otto Struve, for the current published magnitudes of secondaries to be in error, chiefly because they’ve been carried over from older observations, if not the original observation.

That factor was at the heart of the STT double star project. Of the approximately one hundred STT double stars we observed and measured, roughly half of the secondaries had noticeable magnitude errors, some of which were quite significant. We took two approaches to this.  One was an effort to estimate the magnitudes of the secondaries visually, using comparison stars where possible in order to arrive at our estimates.  The results of those comparisons were inconsistent, primarily because the glare from the primaries over-powered the secondaries, which for the most part were visible only with averted vision.  Attempting to hold an elusive and dim star in view with averted vision while at the same time latching onto a comparison star with the same eye is not an approach calculated to succeed every time.  The other was a photographic approach in which Wilfried utilized the facilities of a remote telescope site to determine magnitudes, as well as to produce precise measures of separation and position angle.  That approach proved to be quite accurate and dependable. 

We produced a total of eight papers for the STT series, and as each is published our results are finding their way into the WDS, resulting in a very satisfying and rewarding project.  I’ve listed the eight papers below, five of which have been published so far in the JDSO.  I’ll add links to the remaining three as they’re published. There’s a lot of detail in each of these papers, but the heart of them lies in the two tables near the end, one of which summarize the magnitude findings, and the other which summarizes the separation and position angle measures.

In addition to the STT pairs covered in the JDSO papers, there were another fourteen that didn’t find their way into publication because of other projects, so I’ve decided to cover my observations of that group in the next few Star Splitter posts. Those stars are located in Cepheus, Lacerta, and Lynx. Each of the pieces will be oriented more toward observation than the papers are, so stay tuned for a few star-hopping adventures that will provide you with a chance to test your observational talent and hopefully raise your averted vision skills a parsec or two.

JDSO Articles :

STT Doubles with Large Δ M – Part I: Gem  (with Steve Smith)
STT Doubles with Large Δ M – Part II: Leo and UMa (with Steve Smith)
STT Doubles with Large Δ M – Part III: Vir, Ser, Com, CrB, and Boo
STT Doubles with Large Δ M – Part IV: Ophiuchus and Hercules
STT Doubles with Large Δ M – Part V: Aquila, Delphinus, Cygnus, Aquarius
STT Doubles with Large Δ M – Part VI: Cyg Multiples
STT Doubles with Large Δ M – Part VII: And, Psc, Aur
STT Doubles with Large Δ M – Part VIII: Tau, Per, Ori, Cam, Mon, Cnc, Peg

Problems of a Different Magnitude in Lacerta: 8 Lacertae (STF 2922/A1459) and ROE 47

It had been a long while since I last took a stroll through Lacerta, so I had to grab my well-worn copy of Sky and Telescope’s Pocket Sky Atlas and relocate the constellation’s dim outline between Cygnus and Cepheus.   Lacerta is not one of those constellations that draws attention, which is unfortunate since the Milky Way runs through about 90% of its stellar real estate – meaning it has more than its share of double stars and open clusters. I was back to check on the Lacertan lizard once again because of a question about the magnitude of one of the components of 8 Lacertae, which in keeping with Lacerta’s rich stellar tradition, also has more than its share of stellar companions.   And as long as I was there, I decided to poke around and see what else I could see, which led to a magnitude of additional questions.

Even though it’s the first part of December as I write this, from my forty-five degree latitude Lacerta is almost directly overhead at 7 PM, parked in a holding position between Cygnus, Andromeda, and Pegasus, and Cepheus.

Stellarium screen image with labels added, click to enlarge.

Stellarium screen image with labels added, click to enlarge.

A line drawn from Beta (β) Cephei through Zeta (ζ) Cephei will actually lead you directly to 8 Lacertae:

You can also draw a line from Delta (δ) Cygni (just out of sight at the upper right of the chart) through Deneb, which will just miss the southern edge of 8 Lacerate. (Stellarium screen image with labels added, click to enlarge).

You can also draw a line from Delta (δ) Cygni (just out of sight at the upper right of the chart) through Deneb, which will just miss the southern edge of 8 Lacerate. (Stellarium screen image with labels added, click to enlarge).

But because Lacerta is a dim constellation . . . . . .

Stellarium screen image, labels added, click for a larger view.

Stellarium screen image, labels added, click for a larger view.

. . . . . . you might find it easier to aim an 8×50 or 9×50 finder at 4.5 magnitude 6 Lacertae, move northeast a few degrees to 4.5 magnitude 11 Lacertae, and then drop southeast to 5.1 magnitude 13 Lacerate, using 5.0 magnitude 15 Lacertae as a reference point, and then move south to 5.3 magnitude 12 and 4.9 magnitude 10 Lacertae, which form a triangle with sixth magnitude 8 Lacertae parked in the west corner.   That way you’ll be sure to land on the right star at least.   There should be little chance of confusing 8 Lac with another star since “A”, “B”, and “E” are bright and very obvious:

8 Lacertae  (AB is H IV 86)      HIP: 111546   SAO: 72509
RA: 22h 35.9m   Dec: +39° 38

Identifier      Magnitudes      Separation    PA   WDS
STF 2922 AB:      5.66,  6.29          22.40″   185°   2014
A 1469 AC:      5.66, 10.38          48.90″   168°   2014
A 1469 AD:      5.66,   9.09          81.60″   144°   2014
A 1469 AE:      5.66,   7.25        337.80″   239°   2011
DAL 28 AG:      5.66, 14.08          78.60″   194°   2012
COM 8 BF:      6.29, 10.97         127.60″   175°   2012
A 1469 CH:    10.38, 14.60            1.40″   254°   1932
A 1469 DI:      9.08, 13.30          10.10″   227°   2012
DAL 28 GJ:    14.08, 12.99            6.10″    78°   2009

Distance:  “A” is 2160 Light Years; “E” is 428 LY (Simbad)
Spectral Classifications:  “A” and “B” are B2, “D” is A0, “E” is F0
Notes: Mag of I changed from 11.0 to 13.3 as of 10-29-2015
Magnitudes of GJ are reversed in WDS, should be 12.99 and 14.08

In a mid-October email from Mike Hyrczyk via Chris Thuemen, Mike mentioned he had looked at 8 Lacertae and found the “I” component wasn’t visible in his six inch refractor. At the time, it was listed in the WDS at a magnitude of 11.0, normally well within reach of a six inch scope. That evening, I pointed my six inch f/10 refractor at the complex star and, at 152x, confirmed Mike’s observation. I tried higher magnifications – 253x, 365x, and 380x – and may have had a brief glimpse of the fickle star, but there was no doubt it was fainter than the WDS’s 11.0 magnitude. Chris used a 9.25 inch SCT the following night and basically had the same experience, although he may have detected an elongation in the DI pair. Chris also noticed the magnitudes of the GJ pair were reversed in the WDS, which hasn’t been corrected as of this writing.

Given the 10.10” separation listed for the DI pair, experience told me that a magnitude of 13.0 was about the brightest “I” could be, if in fact I had actually seen it with my six inch refractor in the combined AB glare. A check of photometry records in the UCAC4 catalog showed magnitudes of 13.828 (f.mag) and 13.598 (J and K converted to visual), which were too faint for me to have had a glimpse of the star. I sent what information I had to Bill Hartkopf at the USNO/WDS, who consulted additional photometry records, arriving at a magnitude of 13.30 for “I”.

So — after that long introduction, it’s about time we took a look:

“A”, “B”, and “E” are the stars that catch your eye on first view, all of which are white, followed by “C” and “D”. You have to look a bit closer to get your first glimpse of “F”. The missing “I” component is both too faint and too close to “D” to be seen, as discussed above. There are two more faint pairs to the south of 8 Lac, neither of which are not cataloged in the WDS as double stars. (East & west reversed, click on the sketch for a better view).

“A”, “B”, and “E” are the stars that catch your eye on first view, all of which are white, followed by “C” and “D”. You have to look a bit closer to get your first glimpse of “F”. The missing “I” component is both too faint and too close to “D” to be seen here. There are two more faint pairs to the south of 8 Lac, neither of which are cataloged in the WDS as double stars. (East & west reversed, click on the sketch for a better view).

There’s also an excellent photo and discussion of the 8 Lacertae complex on page 52 of the November issue of Sky and Telescope. Sue French was unable to see “I” with a 10 inch reflector, but found a fifteen inch scope brought it into view, which supports the WDS magnitude change to 13.30.   Sue also noticed the error in the WDS listing for the GJ pair.

8 Lacertae has an interesting history. Sir William Herschel was the first to record it for posterity, cataloging the AB pair as H IV 86 in 1782 (source, sixth title from the top):

Wm. Herschel on 8 Lac

His 84° 30’ south preceding works out to a present day figure of 185° 30’, which is a good match with the current WDS figure, but his separation of 17” 14’” puts the AB pair five arc seconds closer than the WDS data. He describes six stars, which probably correspond to the A through F pairs, although his description of their relative magnitudes is difficult to follow. The Latin phrase at the top of his catalog entry translates as “In the middle of the tail”, which seems to indicate a slightly different configuration for Lacerta than what I show above in the first chart.

Click to enlarge the image.

Click to enlarge the image.

Sirs John Herschel and James South made two observations of 8 Lacertae in September of 1823, which are shown at the right (source, last title on page).  Their measures of AB, which are summarized near the bottom of the page, are in line with the current WDS data, as are their measures of the AD pair (145° 15’, 82.52”, which they refer to as AC).   They seem to have entirely missed the closer 10.38 magnitude star now referred to as “C”.

At the bottom of that same page, they refer to an erroneous measure of the AB pair made by Piazzi in 1800 (212° 58’ and 19.072”). Admiral W.H. Smyth also refers to that error on pp. 519-520 of his Bedford Catalog, as well as William Herschel’s 1782 PA error. Relying on his distinctive pre-Victorian vocabulary to make the point, he wrote: “Here the anomalies are palpably owing to error, and the fixity of the objects appears unquestionable.”

The Admiral was irrefutably correct in regard to the “unquestionable fixity” of the objects.   Given the 2160 light year distance of “A”, little proper motion is exactly what would be expected.   Simbad doesn’t provide a distance for “B”, but it does show “E” to be at 428 light years, which is also far enough away that minimal proper motion would be the norm. I checked the most recent PM data available, which comes from the USNO’s URAT1 catalog, and it confirms the minimal motion for each of the stars:

8 Lac PM Data

Aladin image with labels and data added, click to make the text more legible.

“E” shows the most motion, which again is to be expected since it’s four times closer to us than “A”.   There are no parallaxes available in Simbad on the other components of the system, but judging by their slight motion, they may well be about the same distance as “A”. And at those distance, it’s impossible to come to any conclusion on shared physical motion based on the PM numbers.

Before heading out into the night air to look at 8 Lacertae, I used Sky Tools 3 to take a quick look around the neighborhood for other interesting stars, and quickly found an intriguing multiple star, ROE 47, located just 41’ to the west (here’s our third chart again).   So give your scope a careful nudge in that direction and you’ll be greeted by a sixth magnitude star with several faint companions.

ROE 47        HIP: 111259   SAO: 72446
RA: 22h 32.4m   Dec: +39° 47’

Identifier    Magnitudes    Separation    PA   WDS
ROE 47 AB:    5.90, 11.46        42.90″   155°   2012
ROE 47 AC:    5.90, 12.40        33.50″   341°   2012
ROE 47 AD:    5.90, 12.20      103.70″   216°   2010
FYM 109 AF:    5.90, 14.11        22.00″   106°   2012
ROE 47 DE:  12.20, 12.30          6.60″   175°   2012

Distance: 684 Light Years
Spectral Classification:  “A” is A6
Notes: Mag of C changed from 10.2 to 12.4 as of 10-29-2015
Mag of D changed from 11.36 to 12.2 as of 10-29-2015
Mag of E changed from 9.90 to 12.3 as of 10-29-2015

This one had what you might call a magnitude of problems, but before wrestling with that issue, let’s take a look:

 “A” was very white; “C” was very faint and mainly an averted vision apparition; “B” was distinct; and “D”, which was just a bit easier to see than “C”, was marginally duplicitous at 152x, but it cooperatively separated at 253x with a 6mm Astro-Tech/Sterling Plössl, as shown in the insert below the insert at the right. (East and west reversed once more, click on the sketch to improve the view considerably).

“A” was very white; “C” was very faint and mainly an averted vision apparition; “B” was distinct; and “D”, which was just a bit easier to see than “C”, was marginally duplicitous at 152x, but it cooperatively separated at 253x with a 6mm Astro-Tech/Sterling Plössl, as shown in the insert below the insert at the right. (East and west reversed once more, click on the sketch to improve the view considerably).

It didn’t take but a few seconds to realize that some of the fainter components I was looking at were fainter than the WDS data said they were. As the “C” component flickered in and out of view, I could see it was clearly fainter than the 10.2 magnitude then listed for it in the WDS. There was also something clearly amiss with “D”, which wavered between direct vision and averted vision, meaning it was also fainter than the WDS’s 11.36. And “E”, which was listed at a magnitude of 9.9, was not the conspicuous speck of light it should have been – in fact, it should have been over-powering “D”.   After I separated the DE pair at 253x, it was clear they were both about the same magnitude – so 9.90 was nowhere close to being correct. Chris Thuemen also looked at ROE 47 and basically came to similar conclusions.

There’s a huge amount of photometric data available in both the NOMAD-1 and the UCAC4 catalogs, so I turned to both of those to see what I could find.   Looking at “C”, I found data pointing to a magnitude of 12.3. In the case of the DE pair, the UCAC4 Vmags, which are normally very dependable in this range, showed 11.358 for both stars, which seemed too bright to me.   The UCAC4 f.mag and the J & K visual approximations pointed toward a magnitude of 11.9 to 12.0, which struck me as being closer to what I had seen.

ROE 47 Data Mirror Image

Click to enlarge and make the data more legible.

I sent off what I had to Bill Hartkopf at the USNO/WDS, who used additional data to make the changes I’ve listed at the bottom of the ROE 47 data above. Incidentally, Bill is always quick to say he appreciates these observations very much. With the WDS data base approaching something like 130,000 stars, the only way these kinds of errors get corrected is when visual observers note the discrepancies and report them to the WDS.

Click to enlarge the image.

Click to enlarge the image.

Digging into the history of ROE 47, it appears the AB and AD pairs were discovered in 1895 by E.D. Roe, Jr., a British amateur astronomer, who used a six inch refractor. He added the “C” and “E” components in 1910, as shown in the excerpt at the right from a 1911 issue of the Astronomische Nachrichten.

I couldn’t find any biographical material on E.D. Roe, but it appears he must have had an astronomically dry sense of humor.   If you look at the top left hand corner of the image above, you’ll see he used the Greek symbol “ρ” as an identifier, which in Greek is pronounced rho, as in Roe.  Obviously he liked a good laugh.

Next trip – who knows. The winter rains are here and the few clear skies I’ve seen have had more dancing and twinkling stars than an out of control strobe light at an all-night dance party, meaning atrocious seeing, which is not usual for this time of the year. As soon as the weather cooperates (raining hard now with 60mph gusts of wind), I’ll see what I can find to grace the pages of this blog.

Until then, Clear and Cooperative Skies!  😎

Sleuthing in Sight of Sadalmelik: OΣ 460, Σ 2862, and Σ 2855

If it seems like we’ve been here before, it’s because we have – just a month shy of a year ago, when we looked at “The Alpha-Beta-Gamma of Aquarius,” and discussed Homer-era Greek grammarians, urns of olives, and wine. Those who believe double star discussions have to be relegated to dry recitations of arrid statistics haven’t spent a night with a few ancient Greek star gazers.

On that trip, we discovered Sadalmelik, aka Alpha (α) Aquarii, means “lucky stars of the king”.   Some of that luck seems to have spread to a few nearby stars in the rarified void surrounding Sadalmelik (we’re outside the Milky Way here, so star populations are sparse). I accidentally stumbled over the first lucky star, a tantalizing triple, while surveying some of Herr Otto Wilhelm von Struve’s more difficult discoveries, and it didn’t take long to discover his father, Friedrich Georg Wilhelm von Struve, had also found a couple of visually stunning stars. All three of the stars we’re about to look at are within a two degree radius of Sadalmelik, which will serve as our star base.

Stellarium screen image with labels added, click to enlarge.

Stellarium screen image with labels added, click to enlarge.

Aquarius is a dim and meandering constellation spread out over several acres of sky.   You’ll find it below the west edges of Pegasus and Cetus and north of Capricornus.   Focus your attention on the turquoise α (Alpha) in the chart above because we’re not going to wander far from it.

Here are the locations of our three stars, all labeled in tempting turquoise:

Stellarium screen image with labels added, click for a larger view.

Stellarium screen image with labels added, click for a larger view.

We’ll going to start in the north and work our way south, so let’s move north to OΣ 460, which is located two degrees due north of Sadalmelik. Use 7.57 magnitude HIP 109044 and 6.99 magnitude HIP 109052 to point you in the correct direction. You’ll find OΣ 460 lying in the center of a dim, but distinctive arc of three stars; 7.24 magnitude HIP 109144 lies on its east side, and 8.39 HIP 108990 brackets it on its west side.

OΣ 460 (STT 460)    HIP: 109064   SAO: 127283
RA: 22h 05.7m  +01° 47’
Magnitudes   AB: 8.40, 12.80    AC: 8.40, 12.10
Separations   AB: 13.80”           AC: 18.80”
Position Angles      AB: 340° (WDS 2003)    AC: 30°  (WDS 2003)
Distance: 867 Light Years (Simbad)
Spectral Classification:   “A” is F0

After several frustrating attempts to split some uncooperative sub-arcsecond pairs, I went in search of this tantalizing triple star as a diversion.   My first glance into the eyepiece showed a single star, but when I averted my vision slightly, both “B” and “C” suddenly materialized from out of the primarial glare, which, after wrestling with stars that refused to separate, was a very welcome sight:

Averted vision beauty! You have to look closely to catch sight of the “B” and “C” components, just as I did when peering into the eyepiece. The primary is a weak shade of white. Notice the two UCAC4 labeled stars, which we’ll come back to shortly. (East & west reversed to match the refractor view, click on the sketch for a better view of the faint components).

Averted vision beauty! You have to look closely to catch sight of the “B” and “C” components, just as I did when peering into the eyepiece. The primary is a weak shade of white. Notice the two UCAC4 labeled stars, which we’ll come back to shortly. (East & west reversed to match the refractor view, click on the sketch for a better view of the faint components).

I doubled the magnification with a 5mm eyepiece in hopes of pulling “B” and “C” out of the subdued glare of the primary, which resulted in this slightly improved view:

Although they’ve moved up to direct vision objects, you still have to look closely to catch “B” and “C”. (East & west reversed once again, click to improve the view).

Although they’ve moved up to direct vision objects, you still have to look closely to catch “B” and “C”. (East & west reversed once again, click to improve the view).

 (Click to enlarge)

(Click to enlarge)

At 304x, I was able to confirm my 152x impression that both “B” and “C” are brighter than the magnitudes shown above from the WDS.   Even though it was an averted vision object at 152x, “B” was too conspicuous in my six inch refractor for a 12.8 magnitude star, especially considering it’s parked within 14” of a primary listed as being four magnitudes brighter.   In fact, when compared with the two UCAC4 labeled stars in the first sketch (here it is again), both of which are in the 11.2 to 11.4 magnitude range, “B” was of about the same brightness, allowing for the glare of the primary. I found “C” was slightly brighter than “B”, perhaps in line with the .7 WDS magnitude difference between them, suggesting a magnitude for C in the range of 10.6.

A quick look at the excerpt above at the right from S.W. Burnham’s 1913 Proper Motion Catalog shows he estimated the magnitude of “B” at 11.7 and “C” at 11.0, which is similar to my estimates. STT 460 is part of a joint survey of Otto Struve’s pairs with high magnitude differentials (delta_M) I’m working on, so it will eventually be suggested to the WDS for magnitude revisions.

A glance at the proper motion of the three stars of OΣ 460 shows they appear to be unrelated, since all three are moving in different directions and at differing rates of speed.

A:  +036 -040   (WDS)         (.033”/year east, .038”/year south)
B:  -031 +142   (WDS)         (.031”/year west, .142”/year north)
C: +027 +001   (WDS)         (.027”/year east, .001”/year north)

Now we’ll drop down to Σ 2862, which lies a bit more than a degree (1° 16’) south and very slightly east of OΣ 460. You’ll find it just 24’ east of 6.99 magnitude HIP 109052. (Here’s our previous chart again).

Σ 2862        HIP: 109186    SAO: 127306
RA: 22 07.1m   Dec: +00° 34’
Magnitudes:  8.04, 8.41
Separation:   2.5”
Position Angle: 95°  (WDS 2011)
Distance: 256 Light Years (Simbad)
Spectral Classification: “A” is F8

Spare beauty in a sparse field is the best way to describe this delicate pair:

The primary and secondary are white, almost touching one another, separated by the width of B. It always amazes me how frequently surrounding stars arrange themselves into eye-catching geometric configurations – notice the three stars pointing into the west, lined up almost perfectly with one another. The moon was at first quarter when I made this sketch, about 40 degrees to the west, with moisture practically dripping out of the air, so some of the background stars undoubtedly were obscured at the time. (East and west reversed once more, click to improve the view considerably).

The primary and secondary are white, almost touching one another, separated by the width of B.  It always amazes me how frequently surrounding stars arrange themselves into eye-catching geometric configurations – notice the three stars pointing into the west, lined up almost perfectly with one another. The moon was at first quarter when I made this sketch, about 40 degrees to the west, with moisture practically dripping out of the air, so some of the background stars undoubtedly were obscured at the time. (East and west reversed once more, click to improve the view considerably).

This pair of stars was discovered and measured in 1828 by F.G.W. Struve.   The WDS identifies it as a physical double, which appears to be based on the similar proper motions of the two components.   The WDS data shows “A” with a rate of +078 +049 (.078”/yr east, .049”/yr north) and “B” with a rate of +088 +047 (.088”/yr east, .047”/yr north).

Shown below is a list of measures in Thomas Lewis’s book on Struve’s stars, to which I’ve added two additional measures that I pulled from S.W. Burnham’s 1906 catalog (labeled LM and Hu), three from R.G. Atiken’s 1932 catalog, and four which come from WDS data.

 Click on the image in order to see the data more clearly.

Click for another view.

Based on the proper motion of the two stars, there should be very little detectable change in the relative positions of the two components.   The separation measures in the list above are relatively stable in the 2.3” to 2.5” range, but surprisingly the position angle has consistently moved in a northward direction.   That would lead to the conclusion that either the proper motions numbers are slightly off, or that that one of the two stars could be in a very wide orbit around the other. Some of the preliminary GAIA data is available now in Vizier (the catalog code is I/324) so I checked and found that, unlike the WDS, it lists both stars with the same proper motion, +088.7 +046.6, numbers which are at least similar to the WDS.   At any rate, it’s possible these two stars are doing something more than just traveling the through the galaxy in tandem.

Our last star lies a little over a degree (1°7’) south of Sadalmelik (our chart once again). Drop a short 38’ south and slightly west to 5.29 magnitude 32 Aquarii and then another 32’ south and slightly east to reach Σ 2855, using 9.21 magnitude SAO 145857 to guide you. Notice Σ 2855 forms a triangle with two faint stars, 8.51 magnitude HIP 109141 and 8.93 magnitude SAO 145864.

Σ 2855 (STF 2855)    HIP: 109038    SAO: 145859
RA: 22h 05.3m   Dec: -01° 25’
Magnitudes   AB: 8.34, 10.26     AC: 8.34, 10.80
Separations  AB: 25.10”             AC: 85.10”
Position Angles   AB: 305° (WDS 2013)    AC: 117° (WDS 2013)
Distances   A: 494 Light Years    B: 109 Light Years
Spectral Classifications:   “A” is F8, “B” is G

Spare beauty once more, but we also find ourselves entranced again by a captivating geometric configuration:

The primary was a faint white, and easily the brightest star in a sparse field, while “B” and “C” seemed to be intent on getting lined up perfectly. The first quarter moon mentioned above also had something to do with the lack of stars seen in the field. (East & west reversed once more, click for a much better view).

The primary was a faint white, and easily the brightest star in a sparse field, while “B” and “C” seemed to be intent on getting lined up perfectly. The first quarter moon mentioned above also had something to do with the lack of stars seen in the field. (East & west reversed once more, click for a much better view).

F.G.W. Struve discovered the AB pair in 1828, and I haven’t been able to track down who added the “C” component in 1896.   S.W. Burnham would have been the most likely person, but he didn’t include it in his 1906 or 1913 catalogs, and from what I can determine, Philip Fox and George Hough didn’t measure it either.   I had hoped to get a clue from Aitken’s 1932 catalog, but for some reason he skipped over Σ 2855 entirely.

A look at the distances shown above in the next to last line of data eliminates any question as to whether the AB pair are related, since there’s approximately 385 light years separating the two.   Simbad doesn’t provide a distance for the “C” component, but there is a possibility “A” and “C” are linked physically by proper motion, as the image below shows:

Aladin image with Simbad proper motion data super-imposed. Click to enlarge!

Aladin image with Simbad proper motion data super-imposed. Click to enlarge!

Click to enlarge.

Click to enlarge.

The common motion of “A” and “C” is very obvious, and the proper motion data at the bottom of the images shows the rates of motion are very similar.   “B” is moving more rapidly, which is a function of it being much closer to us.   A look back through the recorded measures is further evidence of the relative motion of “A” and “B”, as you can see the separation (at 25.10″ in 2013) has been narrowing slowly as “B” appears to overtake “A”.   If you happen to be looking up a few thousand years from now, you’ll have the pleasure of attempting to split a very close pair of stars!

Time to go contemplate an urn of Greek olives and a glass of wine, and leave Aquarius to wend its way westward for the remainder of the year.  Our next tour will takes us north to the dense Milky Way star fields of Lacerta, where we’ll see if we can help the Lacertan lizard get a handle on his magnitudes.

Until then, Clear and Stable Skies!  😎

Another Way to Polar Align

LongRefractor1If you’ve been reading this blog for a while, you probably realize I thread my way through the night sky by star hopping.   There was a time when, like many other people, I used a Go-To mount and let it figure out how to get me to where I wanted to go.   But I soon realized I really wasn’t learning my way around the sky, which felt distinctly unsatisfying – kind of like relying on a GPS device to get you from point A to point B repeatedly without taking the time to learn the road and street signs you pass every day.   Given the fact that the skies above me are pretty darn close to magnitude six on a decent night, I decided there was no excuse for being lost most of the time when I looked up. It took a while, but I now know the constellations as well as I know my eyepieces, and there are parts of some constellations that are permanently etched into the corner of my mind reserved for maps.

But to be honest, if I was laboring under the typical light polluted urban sky, I would most likely have felt differently about the whole matter. My experience with light pollution and telescopes is limited to natural pollution, otherwise known as the full moon. It’s certainly possible to star-hop under light blasted skies, but I’ve found the typical 8×50 finder is limited to stars of about 6.0 to 6.5 magnitude when a full moon is hard at work refracting its rays all over a moisture laden sky. Under dark skies I can see stars as faint as 8.5 to 9.0 magnitude in an 8×50 finder, which makes finding my way around much less of a battle than it is when the moon is in charge of things.

If you use an equatorial mount, you quickly learned it needs to be aligned with the north or south pole in order to track an object in right ascension. If, like me, you have a motorized (tracking) EQ mount without GoTo capability, pointing it at Polaris will provide reasonably accurate tracking for most purposes.   But if you stay fixed on an object long enough, you’ll find it drifts from the center of the field of view, which requires you to use the mount’s declination controls to re-center the object.   For low-powered viewing, that’s not much of a problem.

But if the object of your attention requires high magnification, you’ll find yourself constantly re-centering it.   And if you’re trying to sketch the field of view, that perpetual wandering away from the center can make it difficult to accurately represent the stars in the field relative to each other. Which raises two questions: Why does it happen, and What do you do about it?

The answer to the first question is .75 of a degree, which is how far Polaris is from true celestial north. Which is another way of saying Polaris is really not quite the north star you thought it was. At low magnification, that .75 degree difference is minor, but with each increase in magnification, the quicker the object becomes unlatched from the center of the field. The more magnification you add, the sooner it starts to roam — somewhere around 200x you’ll see the object begin to take off almost immediately.   And if you’re a double star observer who finds 300x and 400x to be rather useful on occasion, you’ll find yourself constantly re-centering the object.

The answer to the second question – What do you do about it? – can be summed up in four words: find another north star. Or at least one closer to the actual celestial pole. As it happens, there’s a 9.65 magnitude star located a mere 13.5’ from true celestial north, which goes by several names: BD +89 38, GSC 04661-00002, SAO 3788, and TYC 4661-2-1. We’ll call it SAO 3788 since that’s the name most likely to be used to designate it.

If you’re beginning to feel a bit lost or puzzled, let’s take a look at Polaris in relation to the north celestial pole:

Stellarium screen shot with labels added, click to enlarge.

Stellarium screen shot with labels added, click to enlarge.

As you can see, Polaris is a bit shy of occupying the actual north celestial pole, which is the point at which all the lines converge.   But as you can also see, there are several stars which lie closer to the actual pole, one of which is the previously mentioned SAO 3788.

So now for the main question: how do you get to it?   You star hop to it, of course! Fortunately, we don’t have far to go, so if the idea of star hopping has you on the edge of your seat, despair not. You can do this quite easily from within the field of view of a wide angle eyepiece.

But before we get to the eyepiece view, there are a couple of things we need to pin down, the most important being the positon angle of the ninth magnitude companion of Polaris, which also serves as an important navigational tool.   In fact, we might just as well take a quick look at all the pertinent data on Polaris:

Polaris (Σ 93)  (H IV 1) (Alpha [α] Ursa Minoris)
HIP: 11767   SAO: 308
RA: 02h 31.8m  Dec: +89° 16′
Magnitudes: 2.04, 9.10
Separation: 18.10″
Position Angle: 233° (WDS 2013)
Dist: 432 Light Years
Spectral Type: “A” is F8, “B” is F3

Note the declination of +89° 16′ — further confirmation that Polaris is three-fourths of a degree short of celestial north, in case you still had doubts.

But the key number is the position angle, 233°. We’re going to use that as a reference point for determining which direction to move in order to aim ourselves towards the north celestial pole (which is at 360°). Determining celestial directions in the vicinity of the celestial pole is a very tricky business, even for the experienced observer, and it can be downright confusing when you’re gazing into an eyepiece.  The old trick of turning off your drive motor and letting a star drift across the field of view to determine which direction is west doesn’t work this close to the pole, so a navigational aid is a necessity.

Let’s start by imagining that the the line running from Polaris A through Polaris B stops at the edge of your eyepiece.   We’ll label that point 233°. When we subtract 233° from 360°, we get 127°, which is how far we need to move around the outer perimeter of the eyepiece in order to point ourselves towards celestial north.

Now we’re faced with the big question: which direction do we go? Clockwise or counterclockwise? The answer is that it depends on the kind of telescope you’re using, so pay close attention — it means the difference between success and frustration.  Assuming the use of a conventional inverting star diagonal (NOT an erect image diagonal), if you’re using a refractor or an SCT, north is clockwise from the 233° mark. If you’re using a reflecting telescope (Dobsonian, Newtonian), north is counter-clockwise from 233°. If moving by degrees around the outer perimeter of the eyepiece field is confusing, you can draw a line perpendicular (90°) to the line running between Polaris A and B and then add another 45° to that to point you toward north.

Here’s a diagram which should make all that more clear:

This may look simple when north and south are straight up and down, but that will seldom be the case when you peer into the eyepiece! Click to make the image easier to read.

This may look simple when north and south are straight up and down, but that will seldom be the case when you peer into the eyepiece! Click to make the image easier to read.

And here’s how that move looks when superimposed on our previous chart:

Stellarium screen shot with labels added, click to enlarge.

Stellarium screen shot with labels added, click to enlarge.

Now that we’re directionally oriented in the eyepiece, there’s one more thing we need to discuss before going any further, which is how to move to where we want to be. If you’re new to this, it may come as a surprise, but it’s the mount that needs to move, NOT the telescope.

When you bought your mount, the instructions for it should have covered the procedures for lining up on Polaris. The first thing you would have done is set up your mount so that the declination axis was pointing toward Polaris, and then you would have used the altitude control to move the tilt of the declination axis so that it matched your latitude – in my case, that just happens to be 45 degrees. Then you would have centered Polaris in your finder by using both the declination and azimuth (horizontal) controls on the mount, and then fine-tuned that further by making final adjustments to center Polaris in your eyepiece. During that entire procedure, you would have left the telescope untouched.

So that’s what we’re going to do here.

With the counterweight shaft pointing straight up and down, and the declination circle lined up with the ninety degree mark, lock the declination and right ascension clutches on the mount and then use the altitude and azimuth controls to center Polaris, first in your finder, and then in your eyepiece (if your mount has locks for the altitude and azimuth controls, make sure to unlock them now – and don’t forget to lock them when we’re done!). Here are photos of two frequently used equatorial mounts, which will give you an idea of what to look for in the way of altitude and azimuth controls:

This is a Celestron CG4 mount. The altitude and azimuth controls are unlocked when one of the control devices is loosened, and locked when the two opposite devices are turned so they're pressed against one another. Other mounts, such as the CG5, have similar controls. Click for a larger view.

This is a Celestron CG4 mount. The altitude and azimuth controls are unlocked when one of the pairs of control devices is loosened, and locked when the two opposing devices are turned so they’re pressed tightly against one another. Other mounts, such as the CG5, have similar controls. Click for a larger view.

 

To unlock the azimuth and altitude controls on the Losmandy G11, just loosen the wing nuts shown in the photo -- note there are two, one each on opposite sides of the mount. The Losmandy G8 uses the same setup. Click for a larger view!

To unlock the azimuth and altitude controls on the Losmandy G11, just loosen the wing nuts shown in the photo — note there are two, one each on opposite sides of the mount. The Losmandy G8 uses the same setup. Click for a larger view!

All the movements we’re going to make from this point forward will be made using the altitude and azimuth controls on the mount.

Now if you look carefully at the chart above (here it is again), you’ll see there’s actually an easy way to star hop to SAO 3788. Notice that the Polaris A-B line points almost directly at 6.45 magnitude HIP 7283, which is distinctive because it’s bright and because of the ninth magnitude star located next to it (that star has a name by the way, SAO 223).   And if you move towards true celestial north from HIP 7283, you’ll see it leads you past 8.10 magnitude HIP 3128. And if you extend that line an equal distance, it just happens to lead you to our goal, 9.65 magnitude SAO 3788.

And here’s how that looks when diagrammed, minus the celestial grid in our previous chart:

Stellarium screen image with labels added. (Both this and the previous image portray the scene as it would be seen in a refractor or SCT, meaning east and west have been swapped).

Stellarium screen image with labels added. (Both this and the previous image portray the scene as it would be seen in a refractor or SCT, meaning east and west have been swapped).

Here are those moves once more, but this time plotted on our earlier grid:

Stellarium screen image again, click to enlarge.

Stellarium screen image again, click to enlarge.

So how does all that look in the eyepiece?

Click to enlarge – note, east and west are reversed here to match a refractor or SCT view.

Click to enlarge – note, east and west are reversed here to match a refractor or SCT view.

This is the view with a 40mm Celestron Plössl in a 9.25 inch SCT. I’ve moved Polaris to the eastern corner of the field in order to pull HIP 7283 and HIP 3128 into the field of view.

If you now move toward the north until HIP 3128 is in the same position in the eyepiece as HIP 7283 was, you’ll see our goal, SAO 3788, come into view at the opposite (north) corner of the field of view:

Click to enlarge!

Click to enlarge!

Center SAO 3788 in your eyepiece and you’re now a mere 13.5’ from true celestial north.   Once you’ve done this a few times, you’ll find it’s quick and easy to do.

I’ve found parking SAO 3788 in the center of my eyepiece is more than sufficient for a 400x view — I can barely detect any motion unless I stay on the object for ten minutes or so. Remember, we’ve gone from being 44’ off center from celestial north to 13.5’, which is a huge improvement.

Lock up your altitude and azimuth controls, unlock the declination and right ascension clutches, grab a 4mm eyepiece, and go split that pair of sub-arcsecond stars that’s been on your list for the past year without having to chase it across the field of view!

Happy star hopping and clear skies!

A Closer Look at Eta (η) Lyrae, Including SHJ 289, HLM 19, and SEI 584

Relegated to a blue-white existence well beyond the Lyrae-ian framework, Eta (η) Lyrae beams its fourth magnitude photons at us from about seven degrees due east of Vega, the jewel in the constellation’s crown. Fortunately it isn’t relegated to total stellar isolation, thanks to a surrounding trio of fainter double stars with cooperative separations. In fact, those stars all inhabit the same field of view with Eta (η), providing the observer with a rare four-for-the-price-of-one visual bonanza.

Stellarium screen image with labels added, click to enlarge.

Stellarium screen image with labels added, click to enlarge.

Eta (η) Lyrae was a popular item with the early double-star detectives of the late 18th and early 19th century.  All of them were quick to capture Eta (η) in a telescope, with the result that each of their names became attached to it in the form of the four cryptic catalog designations listed at the end of the title line below.

Eta (η) Lyrae  (Aladfar)  (20 Lyrae)  (Mayer 61)  (H IV 2) (SHJ 291)  (Σ 2487)
HIP: 94481    SAO: 68010
RA: 19h 13.8m   Dec: +39° 09’
Magnitudes    AB: 4.38, 8.58    AC: 4.38, 11.42
Separations   AB: 28.30”          AC: 162.10”
Position Angles   AB: 79° (WDS 2013)   AC: 151° (WDS 2013)
Distance:  1388 Light Years (Simbad)
Spectral Classification:  “A” is B2.5, “B” is A0
NOTE: The catalog designations above, from Mayer 61 to (Σ 2487), refer to the AB pair.

Before we take a look at the historical record, which will include an attempt at decoding William Herschel’s H IV 2 observation of Eta (η), let’s take a peek:

The primary is best described as very white, although it’s also winked at me with a yellow hue on a few previous occasions. “B” stands out quite distinctly despite being four magnitudes fainter than the primary, and “C”, an 1880 addition which is three magnitudes fainter than “B, shines weakly from just outside the southern edge of the primary’s glare. Also seen in the inset at the right are the trio of double stars referred to above. (East & west reversed to match the refractor view, click on the sketch for a much better view).

The primary is best described as very white, although it’s also winked at me with a yellow hue on a few previous occasions. “B” stands out quite distinctly despite being four magnitudes fainter than the primary, and “C”, an 1880 addition which is three magnitudes fainter than “B, shines weakly from just outside the southern edge of the primary’s glare. Also seen in the inset at the right are two of the three double stars referred to above. (East & west reversed to match the refractor view, click on the sketch for a much better view).

Because of its remote location 1388 light years from us, Eta (η) lacks the wanderlust which is typical of stars located within fifty light years or so of planet earth. That’s borne out by the Simbad and WDS proper motion data for both the primary (-001 -001, which is .001”/year west and .001”/year south) and the secondary (+003 +007, or .003”/year east and .007”/year north).   In other words, you would need to hang around for about a thousand years before noticing a barely perceptible difference – and I can think of a lot of things I would rather do over the next thousand years.

But at least Christian Mayer got us started down that road with the inclusion of Eta (η) in his 1779 double star catalog, Tabula Nova Stellarum Duplicium.  Eight more stars were added in a 1781 revision, resulting in Eta (η) Lyrae being designated as Mayer 61, which the resourceful astronomer measured with a separation of 28.3” and a position angle of 81°.

Sir William Herschel turned his telescope to Eta (η) Lyrae on August 29th, 1779, and recorded this observation in his 1782 catalog (twelfth title from the top):

Wm Herschel on Eta Lyrae

The separation of 25.4” he measured was slightly less than Mayer’s figure, while his position angle of 31° 51’ south preceding works out to a puzzling 238° 9’.  Neil English and I have wrestled with Sir William’s Latin on the first line of the observation with little luck – whatever it means, it’s as much a puzzle as the position angle, which was also noticed by Sirs John Herschel and James South on June 16th, 1823 (source for their 1824 catalog, last title on the page):

Click to enlarge.

Click to enlarge.

The stellar Herschel-South duo made two separate measures of Eta (η) Lyrae on the same night, one with a 3.75 inch Dolland refractor (see p. 11 of the 1824 catalog) and the other with a five inch Tulley refractor (the “chef d’oeuvre of that eminent artist”, p.12 of the catalog), which are referred to in their report in terms of their lengths, five-feet and seven-feet, respectively.   Those two instruments are described in detail on pp. 4-14 of their catalog.

Click to enlarge.

Click to enlarge.

When averaged together, the result is a separation of 29.34” and a position angle of 5° 58’ north following, which equates to a present day figure of 84° 2’.   If you look at the individual measures obtained with the two telescopes, you’ll see a noticeable difference between them in separation and position angle.   Also included in their report is an 1819 position angle measure of Eta (η) Lyrae by F.G.W. Struve, 5° 30’ north following, which is our present day 84° 30’.   Struve measured the position angle again in 1830 at 85°, and that time included a separation of 27.90”.   Additional measures up through 1900 are shown at the right, in an excerpt from Thomas Lewis’s book on Struve’s double stars.

It doesn’t happen frequently, but occasionally a position angle gets measured erroneously from the fainter of two stars, instead of from the brighter of the pair.   But that doesn’t explain William Herschel’s position angle for Eta (η) Lyrae of 238° 9’, since adding 180° to the Herschel-South-Struve PA of 84° from 1819 and 1823 results in a figure of 264°.  John Herschel and James South came to the conclusion they and Sir William were measuring different stars, pointing out Struve’s 1819 position angle was essentially in agreement with theirs. Yet when I look at William Herschel’s 1782 catalog entry, his description of the two stars as being “considerably unequal”, as well as his reference to “three other stars in view” (probably referring to the two eighth magnitude stars and one tenth magnitude star arranged in a slight curving arc to the south of Eta (η) Lyrae, the middle one of which is SHJ 289), I don’t get the impression Sir William was looking at a different star.   His separation of 25.4” also supports that impression.

We’ll chalk the puzzling position angle up to what may have been the result of an unusually stimulating and vibrant stellar ether spread invisibly over William Herschel and his telescope on that August night in 1779.   We’ll never know otherwise, so that’s a good place to leave this mystery.

The Surrounding Double Star Trio

Click to enlarge.

Click to enlarge.

The brightest of the threesome of doubles surrounding Eta (η) Lyrae, SHJ 289, was cataloged by John Herschel and James South on June 16th, 1823, the same night they measured Eta.   Once again, as they did with Eta (η), they measured SHJ 289 once with each of their two refractors, resulting in an averaged separation of 40.4” and an averaged position angle of 32° 18’ north following, which translates into a present day figure of 57° 42’.   Those numbers compare favorably with the 2013 data in the WDS shown below. (Here’s the sketch above).

SHJ 289  (H V 42)     No HIP Number   SAO: 68003
RA: 19h 13.5m   Dec: +39° 02’
Magnitudes: 8.01, 8.71
Separation:  39.2”
Position Angle: 56°  (WDS 2013)
No reliable distance known
Spectral Classification:  Ap (“p” refers to “unspecified peculiarity” – see Sky and Telescope here)

William Herschel measured this pair on September 25th, 1781 (about two years after his measure of Eta (η) Lyrae), and cataloged it as H V 42:

Wm Herschel on SHJ 289

He came up with a separation of 38.8” and a position angle of 26° 18’ north following, or as we would say today, 63° 42’, the last figure differing notably from the Herschel-South measure. It’s surprising that these two stars carry the SHJ designation instead of William Herschel’s H V 42 designation, since Sir William provided the first measures for it.   Normally that’s the criteria for determining what prefix is attached to star, but as in this case, there are exceptions to the rule.

Simbad doesn’t list a parallax for either of the SHJ 289 components, but Stelladoppie reports a distance of 11,248 light years, which is too distant to be accurate if based on parallax. The most recent proper motion data from the URAT1 survey lends support to the idea that the two stars are rather distant from us, with motions reported for A of -007.3 +001.8 (.0073”/yr west, .0018”/yr north) and for B of -005.6 +001.2 (.0056”/yr west, .0012”/yr north). Translated into everyday language, the inherent motion of the two stars barely qualifies as a crawl.

Located 5.75′ due west of Eta (η) Lyrae is another pair of stars known as HLM 19 (here’s the sketch above once again).

HLM 19    No HIP or SAO
RA: 19h 13.2m   Dec: +39° 08’
Magnitudes: 11.30, 11.87
Separation:   12.4”
Position Angle: 330° (WDS 2013)
No distance or spectral classification

The three letter prefix for these two stars belongs to Edwin Holmes, who discovered them sometime around 1900. According to this article by T.E. Espin, some of the position angles in the stars discovered by Holmes were in error, so he and M.A. Ellison made more precise measures in the early 1920’s. The first date of measure for HLM 19 in the WDS is 1922 (11.8”, 332°), which Espin made, and can be seen at the bottom of the first page of the article in the link above.

Holmes is also known for his 1892 discovery of the comet known as 17P/Holmes, which put on a spectacular display in the autumn of 2007.   Holmes’ account of his discovery can be read here, and there’s also a detailed biography of him here.

Located 7’ northeast of Eta η Lyrae is the last of the trio of surrounding double stars, SEI 584 (here’s our earlier sketch once more):

SEI 584    No HIP or SAO Numbers
RA: 19h 14.3m   Dec: 39° 11’
Magnitudes: 10.74, 11.60
Separation:   25.2”
Position Angle: 118°  (WDS 2010)
No distance or spectral class

The SEI in SEI 584 belongs to Julius Scheiner, who was a pioneer in astrophotography and spectral analysis. A biography of him by Edwin Frost is available here.

No distance or spectral class is available for this pair of stars, but as was the case with SHJ 289, the URAT1 proper motion data indicates they’re located a respectable distance from us.

Click to enlarge.

Click to make the date more legible.

Translated, the proper motion numbers are telling us A is moving east at a rate of .0061” per year and south .0074” per year, while B is moving east at the rate of .0015” per year and south at the rate of .0159” per year, which again is a relative crawl compared to stars located within fifty light years or so from us.  Judging by the motion of A relative to B, it doesn’t appear the two stars are gravitationally linked.

That’s it for this trip through Lyra — not sure yet where the next stopping point is, so stay tuned.

Until then, clear and stable skies! 😎

From 68 Herculis (OΣ 328) to 72 Herculis and Beyond to H N 5

If you look at a star atlas (for example, chart number 52 of Sky & Telescope’s Pocket Sky Atlas), just a few degrees east of the Herculean keystone you’ll find a pair of fifth magnitude stars dominating a relatively barren star-scape. They’re 68 and 72 Herculis, the first a rather difficult pair which I found to be surprisingly less difficult to split than it should have been, and the second surrounded by a multitude of scattered components. In between these two stellar sign posts are additional faint double and multiple stars, some of which offer interesting places to pause and ponder while negotiating the interstellar interval between 72 and 68 Herculis.  And we’ll make an additional short hop through the darkness east of 72 Herculis to wrestle with the mysterious HN 5.

Here’s a wide view of the location:

Stellarium screen image with labels added, click to enlarge the image.

Stellarium screen image with labels added, click to enlarge the image.

And here’s a close-up of the area:

This is an Aladin image of the area with all the double and multiple stars in the immediate area of 68 and 72 Herculis labeled.   Click for a larger image.

This is an Aladin image of the area with all the double and multiple stars in the immediate area of 68 and 72 Herculis labeled. Click for a larger image.

We’ll start with 68 Herculis, aka OΣ 328, which, as our first chart above shows, lies midway between Pi (π) and Epsilon (ε) Herculis, and about two degrees east of the line which connects those two stars.

68 Herculis  (OΣ 328/STT 328)      HIP: 84513   SAO: 65913
RA: 17h 17.3m   Dec: +33° 06’
Magnitudes: 4.8, 10.2
Separation:  4.2”
Position Angle: 59°  (WDS 2001)
Distance: 665 Light Years (Simbad)
Spectral Classification: “A” is B 1.5

When I first saw the magnitudes of the primary and secondary, along with the separation, my first thought was that it would be pointless to try to resolve this pair with either my six inch refractor or 9.25 inch SCT. My experience has been that a pair of stars with a magnitude differential of four (usually referred to as the Delta_m) with a four arc second separation is right at the extreme visual limits of both the six and the 9.25 inch scopes.  This pair has a Delta_m of 5.4, which should have put it out of reach.

But when I saw the amazing photo below taken by Steve Smith, I reconsidered:

West is at the left to match the refractor image in the sketch below.   Click to improve the view!   (Photos used with the kind permission of Steve Smith).

West is at the left to match the refractor image in the sketch below. Click to see the secondary more clearly.  (Photos used with the kind permission of Steve Smith).

So armed with a slight ray of hope and a couple of photon absorbing Plössls, I pointed the six inch f/10 refractor up toward the zenith and took a seat.  The seeing that night was average (III on this scale), but near the top of the sky it was slightly better (something close to a IV on that same scale) — although for very short periods of time it was actually quite steady.  I had no luck with a 10mm Radian (152x), which was no surprise, and after several minutes of patient waiting, also struck out with a 6mm Astro-Tech Plössl (253x).  For whatever reason, that eyepiece does a rather good job of suppressing the glare around a primary, so I didn’t expect to do any better with the next step up in magnification.

The choice for that step fell on a 4mm Astro-Tech Plössl (380x), which isn’t quite as effective with the glare — but if you don’t try, you’ll never know.  After something like ten minutes of careful study, I managed to catch a slight elongation in the primary at the correct PA with averted vision.  Then suddenly a faint, but very distinct, point of light popped into view, lingered for a tantalizing second or two, and disappeared.  After another couple of minutes, it re-appeared for slightly longer, and then vanished.  I went back to the 6mm for a few minutes to relieve my strained eyes, didn’t see anything, went back to the 4mm once again for a few more minutes, but still failed to see any sign of the elusive secondary.

Unlike the averted vision elongation of the primary, which was rather smeared and unfocused, the faint point of light I saw was quite clear, even though it was also an averted vision object.   This sketch provides a reasonably good idea of what I saw, but keep in mind, the image was nowhere near as steady as what you see here:

First, enlarge the image to see the secondary, and then imagine trying to hold that faint point of light in view with averted vision while it bounces around at something like ten or fifteen times per second!   East and west are reversed to match the refractor view.

First, enlarge the image to see the secondary, and then imagine trying to hold that faint point of light in view with averted vision while it bounces around at something like ten or fifteen times per second!  East and west are reversed to match the refractor view.

Click to enlarge.

Click to enlarge.

While looking up the data on this star, I noticed it was a variable – in fact, the S&T Pocket Atlas identifies it as u Herculis. (NOTE: there’s also a U Herculis – upper case “U” – which is not 68 Herculis).  A search on the AAVSO site for “68 Her” turned up the data at the right, which shows it’s an eclipsing variable (click on the question mark at the right side of the “Variability type” line) with a variation in magnitude from 4.69 to 5.37 over a cycle of 2.05 days.  The light curve for 68 Her shows the dimmest part of the cycle is rather brief, so the odds of catching the pair at maximum elongation are pretty good.  It’s also quite possible the secondary is a bit brighter than the 10.2 magnitude listed for it in the WDS, which would make it slightly easier to see.

However, I noticed James Kaler places the distance between the two stars at .07 astronomical units, which amounts to fourteen times the sun’s radius.  If that’s the case, there’s another star involved here in addition to the one Steve photographed and I saw.  The 4.2″ separation of the pair at a distance of 665 light years means they’re much farther apart than fourteen solar radii.   The WDS, by the way, makes no mention of a third component.

Next stop is 72 Herculis, which lies a degree southeast of 68 Herculis (here’s our second chart again).

72 Herculis       HIP 84862   SAO 65963
RA: 17h 20.7m   Dec: +32° 28’

Identifier    Magnitudes   Separation    PA WDS
DOR 1  AB:    5.45, 10.78      308.10″   340°  2002
ARN 14 AD:    5.45,   9.01      396.40″    60°  2013
ARN 14 AE:    5.45, 10.36      302.20″    51°  2002
ARN 14 AF:    5.45, 10.37      383.20″   104°  2002
DOR 1  BC:  10.78, 13.30         6.20″   247°  2002

Distance: 46.7 Light Years (Simbad)
Spectral Classification:  “A” is G0

This is what you might call a far-flung sextuplet of mostly faint stars. The inset at the right of the sketch shows all of the members, with the exception of the unresolvable “C”. Note the 12.6 magnitude star located between “A” and “F” which hasn’t been included in the system. You’ll also notice two more double stars in the field of view, GBC 28 and BU 630, which we’ll come back to shortly. (East & west reversed, click on the sketch for an improved view).

This is what you might call a far-flung sextuplet of mostly faint stars. The inset at the right of the sketch shows all of the members, with the exception of the unresolvable “C”. Note the 12.6 magnitude star located between “A” and “F” which hasn’t been included in the system. You’ll also notice two more double stars in the field of view, GBC 28 and BU 630, which we’ll come back to shortly. (East & west reversed, click on the sketch for an improved view).

Click to enlarge the page.

Click to enlarge the page.

The first thing that intrigued me about 72 Herculis was its three letter identifier, DOR.   The references and discoverer codes in the WDS show DOR stands for Dorpat Observatory, referring to the observatory at Dorpat (now Tartu) in Estonia which was under the control of F.G.W. Struve until the mid 1830’s.   Confusing the issue is the first observation date in the WDS, 1853, which is almost twenty years after Struve left Dorpat for the Pulkovo Observatory, located south of St. Petersburg in Russia.   A check of Burnham’s 1906 double star catalog shows him referring to 72 Herculis as σ 544, and a check of Burnham’s list of references (p. vii) shows the lower case Greek letter “σ” (Sigma) refers to Dorpat Observations, Vol III, which was originally entitled Catalogus 795 stellarum duplicium, published in 1822 by F.G.W. Struve.

Since many of the more obscure Dorpat publications aren’t available on the internet, I didn’t expect to find Catalogus 795 stellarum duplicium, but fortunately it was available through Google books, and the result is the page you see above.   The third column lists Struve’s estimate of the magnitude of the primary, and the next two are the right ascension and declination – which means there were no measures of PA and separation published in this catalog.   At the bottom of the page is a perplexing note referring to the asterisked “a)” in the first column.   Since I don’t have a Latin background, I ran the sentence through Google’s translator, which garbled it badly.   Other translation engines didn’t do any better, so I checked with Neil English, author of several books on astronomy, who is well versed in Latin.  His translation is “I did not find the separation of 72 Herculis to have increased as/where it ought to have.”  That raised another question, which we’ll circle back to shortly.

Like its neighbor, 68 Herculis, 72 Herculis is also a variable star, although with a narrow range of magnitudes, 5.38 to 5.45.   Unlike its neighbor, though, 72 Herculis is much closer to us (over 600 light years closer, in fact), which is reflected in its rather high rate of proper motion.

The image is from Aladin – click to enlarge and to make the date below more legible.

The image is from Aladin – click to enlarge and to make the date below more legible.

The arrows shown on the photo are from Simbad, while the data below the photo comes from NOMAD (there’s very little difference in the proper motion rates listed in the two catalogs).  The data shown for “A” shows it moving east at .135”/year and south at a much faster rate of 1.041”/year (rounded off to three decimal places), which makes it a relative speed demon in comparison to most stars.

As you can see by just looking at the arrows, 72 Herculis A is a foreground star that’s moving relatively rapidly against the backdrop of its components, which are obviously unrelated to it.  Their inclusion provides reference points for establishing and verifying the rapid motion of 72 Herculis A.  With the aid of Simbad’s data and Aladin’s epoch plotting tool, I was able to put together this plot which shows the motion of 72 Herculis A in relation to the five components from 1800 to 2000:

Aladin image once again, click to enlarge!

Aladin image once again, click to enlarge!

If you had turned a telescope on 72 Herculis in 1800 (or in approximately 1822 as F.G.W. Struve did), 72 Her A and B would have been a more convincing visual pair, with a separation of 114” versus the 2002 WDS measure of 308.10” – quite a difference, to say the least.  Not quite warp speed, but still pretty darned impressive.

That takes us back to Struve’s comment about the separation of 72 Herculis not having increased as it should have.  Did he realize 72 Herculis A had a high rate of proper motion?  It’s highly unlikely, since there would have needed to be some previous observations of it.  Neither William Herschel or Christian Mayer include 72 Herculis in their catalogs, so Struve’s comment is still difficult to understand.

The Interstellar Interval

In between 68 and 72 Herculis are a handful of double and multiple stars that can be used to test your visual acuity and patience, two of which are shown in the sketch above of 72 Herculis.   Here’s a chart, taken from Aladin, with each of the stars identified and their data shown below:

Click to enlarge and to make the text below the image legible.

Click to enlarge and to make the text below the image legible.

I looked at all of these and had some degree of luck with each one, with the exception of POP 222 – with a 3.8 magnitude differential and a faint 12.32 magnitude secondary, plus the poor seeing, it was beyond reach that night.   One word of caution if you look this one up in Stelledoppie: as of this writing, the HIP and BD numbers shown for it are in error – they actually refer to HU 1185 (WDS 17591+3228) instead of POP 222.

GCB 28 was a tough one to separate, given the faint magnitudes and tight separations, but I managed several phantom-like averted vision glimpses of two of the three stars at 380x (using a 4mm TMB Planetary II).  The “B” component is located about one arc second northeast of the primary, putting it beyond reach due to the poor seeing.  I also needed 380x to detect an elongation in BU 630.  BU 45, on the other hand, was easily visible at 84x as an impossibly small and tight twin dots of light.  I included it at its approximate location in the bottom left corner of the sketch of SEI 542 shown below:

This pair (in the center of the field of view) can also be seen in the Aladin image above as two separate stars – at a separation of 28.80”, they’re easily resolved, provided you have enough aperture to pick out the 12.2 magnitude secondary.   (East & west reversed once again to match the refractor view).

This pair (in the center of the field of view) can also be seen in the Aladin image above as two separate stars.  At a separation of 28.80”, they’re easily resolved, provided you have enough aperture to pick out the 12.2 magnitude secondary.  (East & west reversed once again to match the refractor view).

Also shown at the bottom left of the SEI 542 sketch is BU 628, another pair that was well beyond my optical reach due to its separation of 0.5”.  However, this one is a true binary with a reasonably well determined orbit, which can be seen here.

The Mysterious HN 5

Our last stop on this tour is HN 5, which is located 51’ east and slightly south of 72 Herculis.  If you position 72 Her at the north edge of your field of view and nudge your scope to the east, the “A” and “D” components of HN 5 will pop into view. Here’s an Aladin photo, which shows both components clearly, and if you look closely, you’ll see “B” and “C” parked on opposite sides of “A”.

Aladin image with labels added, click to enlarge.

Aladin image with labels added, click to enlarge.

HN 5      HIP: 85191   SAO: 66016
RA: 17h 24.6m   Dec: +32° 15’

Identifier Magnitudes Separation   PA WDS
HN 5 AB: 8.65, 12.50       24.6″  356°  2002
HN 5 AC: 8.65, 12.20       37.3″  181°  2002
HN 5 AD: 8.65,   8.98     151.1″   15°  2003

Distance: 692 Light Years (Simbad)
Spectral Classes:  “A” is K5, “D” is M2

Both “A” and “D” have a yellow-orange-gold tint if you look closely, which would be more pronounced if the two stars were brighter.   I had to look carefully to get my first glimpse of “B” and “C”, both of which were averted vision objects. I found “C” popped into view first because it’s a bit further from the primary – under better seeing conditions, it should be possible to see it with direct vision. Judging from their tendency to be slightly elusive, the magnitudes listed for them in the WDS appear to be about right.   (East & west reversed once again, click on the sketch for a better view).

Both “A” and “D” have a yellow-orange-gold tint if you look closely, which would be more pronounced if the two stars were brighter.  I had to look carefully to get my first glimpse of “B” and “C”, both of which were averted vision objects.  I found “C” popped into view first because it’s a bit further from the primary – under better seeing conditions, it should be possible to see it with direct vision. Judging from their tendency to be slightly elusive, the magnitudes listed for them in the WDS appear to be about right.  (East & west reversed once again, click on the sketch for a better view).

So why the title above describing HN 5 as mysterious?   First, let’s take a look at Herschel’s description of if it in his 1822 catalog (source):

Click to enlarge

Click to enlarge

Herschel’s account shows he discovered this group of star in 1784, but apparently too late to get them into his 1784 catalog. The mystery here lies in his reference to the position of the stars he was looking at.  He seems to place 58 (Epsilon) Herculis to the north at a distance of 1° 22’ (no idea why he included “f. 22′ 42” ahead of 1° 22’), but the problem is HN 5 is located five degree east and 1 degree north of 58 Herculis.  When I ran his coordinates through a precession calculator, the resulting coordinates for 2000 are very close to those in the WDS for that date.  So it would appear he was looking in the correct location, but then there’s that diagram of the stars which he included – it doesn’t come close to matching the configuration of HN 5.  I’ve tried flipping and rotating my sketch to match the orientation of the Newtonian scope he used, but still can’t come up with a match for his sketch unless I include stars considerably fainter than HN 5 “A” and “D”.

However, when I looked 1° 22’ south of 58 (Epsilon) Herculis, I found 7.86 magnitude HIP 83152, which is located at a distance 1° 23’.  Just to its northwest is a distinctive parallelogram of eleventh magnitude stars, the center of which is 1° 20’ from 58 (Epsilon) Herculis:

Aladin image once again, click to enlarge.

Aladin image once again, click to enlarge.

Their configuration is very similar to those in Herschel’s diagram, but they aren’t oriented at the same angle.  Herschel normally observed at the meridian, so it’s unlikely he would have changed the orientation of his sketch from the actual appearance of the four stars.

At any rate, the HN 5 he saw is not the group of stars currently designated as HN 5.  In fact, it appears S.W. Burnham was the first to measure all four of the stars which currently make up HN 5, as shown in the excerpt below from his 1906 catalog:

Click to enlarge.

Click to enlarge.

Notice his comment “identified and measured”, which would indicate he was specifically trying to identify the stars at the location provided by William Herschel.

Of course, it’s always possible proper motion would distort the positions of stars, although it’s highly unlikely there would have been enough to change their appearance drastically between 1772 and 1903/1905.  But just for the sake of looking, here’s what I found:

Click to enlarge.

Click to enlarge.

That data shows “A” moving west at the rate of .010”/year and south .021”/year, while “D” is moving west at the rate of .003”/year and north at .018”/year, which is nowhere near enough to cause a drastic change in the orientation of the four stars.  And “C” and “D” are moving even less.

So we’ll probably never know what Sir William Herschel was looking at when he cataloged HN 5.  Once again, the solution to another stellar mystery remains locked up in the black vault of interstellar space.

Back soon with another stellar adventure.   Until then, clear skies!  😎