Ice cubes in the water jar – Zeta (ζ) Aquarii and friends

Zeta (ζ) Aquarii   (H II 7) (Σ 2909)       HIP: 110960   SAO: 146107
RA: 22h 28.8m Dec: -00° 01′
Mag: 4.34, 4.49  Sep: 2.3″ PA: 166° (WDS 2013)
Distance: 103 ly
Spectral type: F3 IV-V

(WDS data updated 9/13/2014)

It’s almost Neptune’s birthday, otherwise I would not be prowling around this particular section of sky – it tends to look empty  and the constellations that do fill it use a lot of fourth and fifth magnitude stars and when you connect the dots they seldom  look like their names imply –  but oh what a beauty I have been missing – Zeta (ζ) Aquarii. It’s easy to find, can be split with a 60mm, and yields a closely matched pair with the slightest tint of colors.

But I’m jumping ahead of the game – this year Neptune is in Aquarius and completing it’s first Neptunian “year” – almost 165 years since it’s discovery. You can read all about it here, including star-hopping charts and instructions. But when I went to that section of sky the other night and found  Neptune peeking barely above my tree line – I got thinking about what else might be here and that “water jar,” or “Y” really caught my eye. It is practically dead on the celestial equator and so should be visible to much of the world.

Here’s the general vicinity I’m talking about.

Click image for much larger – readable – version. Looking south on a Summer morning you’ll see the general region that includes our target double. There are only two, bright “guidepost stars” in this region, Altair and Fomalhaut, and except for the  familiar “teapot” the asterisms tend to be made of fourth and fifth magnitude stars and are best seen in binoculars. What I’ve labelled the “Arrowhead” is a good deal of the constellation Capricornus. The pair of stars at the northeastern tip, which includes Deneb Algiedi, are easy to find and a good guide.  The “Circlet” and the “Water Jar” itself can be seen with the naked eye if your skies are reasonably free of light pollution, but are easier targets for binoculars. (Prepared from Starry Nights Pro screen shot.)

It was about 2 am and though the water jar was faint, it was well above my tree line. The whole asterism just fit in my 15X70 binoculars – lower power ones with a wider-field would do better.  Checking the charts I found the central star of this 4-star asterism is a double – not only a double, but one Sissy Haas rates as a “showcase double” and with good reason. Here’s a closer view.

Click chart for a much larger version. I included the insert from the Johann Bayer. Uranometria atlas of 1603 to help you understand why it’s called the “water jar” because there’s no way this asterism look like any water jar I’ve ever seen. (Prepared from Starry Nights Pro screen shot.).

There’s a hint of color here. The brighter one seemed  to hold a slight tint of lemon in the 85mm refractor. The other a hint of grey.  Sissy Haas says they have a pretty color “whitish citrus orange.” In the 60mm I had to crank up the power, got a hairline split, and saw no color.

But here’s what really delights me about Zeta Aquarii.  I see it as part of a wonderful sequence of similar doubles that if viewed in succession would give one a practical lesson in the meaning of “separation.”  The others are Nu Draconis, Gamma Arietis, and Porrima. Along with Zeta Aquarii these four are each made of a pair of stars that are nearly equal in brightness and the pairs each orient in a roughly north/south direction. But they differ signifcantly in separation.

At 63.4 seconds, the 5th magnitude pair in the dragon’s head can be split with binoculars if you can hold them steady enough.  The “Ram’s Eyes,” Gamma Arietis, are a beautiful sight in just about any small telescope being at the breaking point between 4th and 5th magnitude and separated by 7.5 seconds. The Zeta Aquarii pair is just a bit brighter, but more of a challenge. Haas list the spearation as 2.0 seconds. To me they seemed a bit wider than that because I found them so much easier to split than Porrima. Porrima, in the spring of 2011, has given us more of a challenge with a separation of  1.7 seconds and a brightness that puts them right on the borderline between third and fourth magnitude.

Of course, all of these aren’t well placed for observing at the same time, but all could fit into the same July night.  Porrima would be first on the agenda, low in the southwest after sunset and still a challenge object.

Porrima  (Gamma {γ} Virginis), also designated as Σ1670 (STF 1670)
RA: 12h 42m    Dec: -01° 27′
Magnitudes:  3.48, 3.53  (WDS 2009)
Separation:   1.7″  (Spring 2011)
Position Angle:    44° (2010)
Distance:   38 Light Years
Spectral Type: F0, F0

Go here for details.

Sometime after midnight you should get a good shot at the Dragon’s Head and Nu Draconis.

Nu (ν) Draconis

RA: 17h 32m Dec: +55°11′
Mag: 4.88, 4.86 Sep: 63.4″ PA: 311°
Distance: 99 ly
Spectral type: A6, A4

Go here for details.

In the early morning hours Zeta Aquarii is best places. And the for the Ram’s eyes  (Gamma Arietis) ot’s best to wait until just before astronomical twilight begins a couple hours before sunrise. Then it should be well placed in the eastern sky.

Ram’s Eyes  – Mesarthim – (Gamma [γ] Arietis)
RA: 01h 53.5m   Dec: +19° 18′
Mag: 4.5, 4.6   Separation: 7.5″  PA: 0°
Distance: 204 LY
Spectral Classification: B9, Ap

Go here for details. 

16 and 17 Draconis – Twin to the famous Dragon’s Eyes plus more

16, 17 Draconis
RA: 16h 36m Dec: +52°55′
Mag: 5.4, 5.4 Sep: 90″ PA: 196°
Distance:  400 ly
Spectral type: B9.5, B9

17 Draconis
RA: 16h 36m Dec: +52°55′
Mag: 5.4, 6.4 Sep: 3″ PA: 196°
Distance:  400 ly
Spectral type: B9.5, B9

These two – 16 and 17 – are an easy binocular pair – and as such a nice warm up for the more challenging (and half a magnitude brighter)  binocular double  Nu (ν) Draconis known as the Dragon’s eyes. Turn a telescope on 16 and 17 and the challenge takes a new twist – trying to split  17, a close pair of stars separated by 3 arc seconds and a single magnitude.  (Seventeen is north of 16.) That makes 17 very similar to nearby Mu (μ)  Draconis where the split is closer – 2.3 arc seconds – but there is no difference in magnitude. In fact, that makes this little area of sky near the Dragon’s head a real neat playground. You can start with the original Dragon’s Eyes because they’re easiest to find, then slide west about 4 degrees to Nu and west another 4.5 degrees to Mu. Real cool. Here’s a finder chart.

Click chart for larger version. Chart created from Stellarium screen shot.

I can split Mu with 10X50 binoculars, but it’s a real challenge for me to hold them steady enough. Much easier to  do if I mount them. However, 16 and 17 have a split that’s half again as wide while they’re nearly as bright and so they split more easily in binocular or finder.

I used an 80mm APO with a 6mm zoom to get a clean split of 17. All three stars are nearly the same color, though for me the secondary to 17 had a pale violet tinge. If you can split this close pair, try the same telescope and eyepiece on Mu. It would be interesting to see if you find it  easier – or more difficult to split than 17. On the one hand it should be more difficult because the stars of Mu are closer together. On the other, it should be easier because the Mu stars are the same magnitude whereas the 17 stars are separated by a magnitude.

What really strikes me about these stars, however, is the way that in such a small area of sky we have three pair of stars that qualify as “Dragon eyes” – that is, the stars in each pair are the same color and brightness – and a fourth pair – 17 – that almost qualifies, though there the secondary is dimmer. Hmmm . . . and which a stars are really the brightest? The honor goes to 16 and 17, since they are about 400 light years away – at least  four times farther than the Nu or Mu Draconis pairs!

Nu (ν) Draconis – the eyes of the dragon

Nu (ν) Draconis
RA: 17h 32m Dec: +55°11′
Mag: 4.88, 4.86 Sep: 63.4″ PA: 311°
Distance: 99 ly
Spectral type: A6, A4

OK, I haven’t heard Nu (ν)  called that exactly, but why not? Whoops – stop the presses! Just checked and Sissy Haas calls Nu “The Dragon’s Eyes!”  Darn. And I thought I had a new idea  – the older I get the more I steal – unwittingly, of course 😉

This pair of bright, beautifully matched stars certainly qualifies as eyes and they are easily found in the head of Draco. And look at those stats! In brightness there is just .02 magnitude difference. (As a variable star observer I learned to detect in tenth of a magnitude increments, but nothing smaller with any hope of accuracy.) And the spectral class is almost exactly the same and indicates the pair of white stars most of us report seeing. What’s more, they’re easy and fun to find and an excellent challenge object for hand held binoculars! I’ve seen them with 10X50 steadied on something,  and found them quite easily split with 12X36 IS. They are a pleasure in mounted 15X70s or 20X80s and the 60mm Unitron  I was using this morning almost felt like overkill, even at 28X!. Still, this is what I call a 60mm Jewell! Here’s a finder chart. Click on it to get a larger version.

To find Nu just chart a path between Vega and the Guardians of the Pole. Nu is the faintest of four stars that make up the dragon's head. (Conveniently, these stars are 2,3,4, and 5th magnitude!) Derived from Starry Nights Pro screen shot.

Incidentally, when I Googled Nu I met myself – that is, I found that several posts I’ve put in my observing blog reference it and end up bunched fairly high  on the Google list. For various reasons with various instruments, I have returned to this pair again and again. See the lists of posts here.

Oh – and don’t miss the lesser Dragon eyes – here. We’re talking Nu (ν) and Mu (μ) – binoculars and telescope – oh, and Epsilon (ε) figures into the mix as well. There’s a feast in the beast – for the eyes, at least! (Sorry – couldn’t resist.)