It always amazes me what gems lurk in the dark of the night, waiting patiently for an unsuspecting Star Splitter’s unannounced visit. I’ve been at this long enough now that it would seem there can’t be too many of those jewels left. I won’t bet on it, though. Every time I think I’ve rounded the last one up, another one drifts into view from wherever they drift into view from.
I usually start an observing session with one or two specific targets in mind and let the stellar muse take over from there. Sometimes I’ll spend the whole night on one or two objects, other times I’ll finish up quickly with them and track down old favorites or neglected should-be-favorites. And occasionally I’ll run through all of those and find myself with unexpected time on my hands. That’s what happened on the night I discovered the two stars we’ll look at now.
I had exhausted my mental catalogue of stellar targets, as well as myself, so I took a break to brew a cup of tea and raid the cookie jar. While the water was boiling, I picked up Sissy Haas’s book, flipped to Leo, and scanned through it to see what I could find north of the Lion’s back. It wasn’t long before I came across this description of 54 Leonis on page ninety-two — “Showcase pair. 60mm: A bright, easy pair with lovely contrast — a bright banana-yellow star and a smaller sapphire blue, split by hairs at 45x. Webb: ‘Greenish white, blue.’ “ — so I poured the tea, grabbed the cup, parked a couple of cookies in my pockets, and headed out into the dark of the night once more.
54 Leonis (STF 1487) (Sh 117) (H III 30) HIP: 53417 SAO: 81584
RA: 10h 55.6m Dec: +24° 45’
Magnitudes: 4.48, 6.30
Position Angle: 111° (WDS 2012)
Distance: 289 Light Years
Spectral Classifications: A1, A2
If you look at the chart above (this will help), the easiest way to get to 54 Leonis is to follow the line that runs from Denebola [Beta (β) Leonis] to Zosma [Delta (δ) Leonis], then extend it about two-thirds of that length and incline it a slight bit to the north. That will lead you directly to 54 Leonis, which conveniently forms a triangle with the two sixth magnitude stars above it, 48 and 50 Leonis Minoris.
54 Leonis is a classic example of the kind of trick a close pair of reasonably bright stars can play on your eyes. On first glance, I thought maybe I had taken a wrong turn — the “banana yellow’ and “sapphire blue” were absent without leave and white had taken their place. According to their spectral classifications, these two stars should appear white or bluish-white to the critical Star Splitter eye. And they do — sort of — or at least to start with — some of the time — usually. What happened was that as I looked at them a little longer, I discovered a slight shift towards pale yellow taking place in the primary, and at the same time the secondary began picking up traces of a very subtle blue. The colors seemed to creep in very gradually, as if some unseen creature was adjusting a color-control knob:
The more I looked, the more colorful those colors became. The energy for that increasing intensity of color seemed to be coming from a remarkable and very uncanny interaction of starlight dancing across, or in, or between, the gap separating the primary and secondary.
After I had written the description above, Pat Conlan posted a comment on 54 Leonis which led me to this post Greg wrote about it a couple of years ago, which I had totally forgotten about. Normally we avoid repeating posts on the same star, but in this case, the experience the three of us had with the colors of 54 Leonis provides some very interesting, not to mention head-scratching, reading.
If you go back and read Greg’s post, you can see right away from his title he saw “whiter than white.” And if you read further, he also saw yellow in the primary at 60mm’s of aperture (the secondary was a puffball), but in an eight inch SCT the primary went white and the secondary became pale blue. Meanwhile, Pat was using an 80mm refractor and saw yellow in the primary and blue in the secondary using a 16mm Ortho — until he switched to a 10mm Ortho, which resulted in the primary shifting toward white and the blue becoming less blue. And on an observation that took place a couple of nights later, the primary was now white in the 16mm Ortho, but then shifted to yellow in the same eyepiece with the same scope.
Hmmm — puzzling and perplexing.
OK, so what colors have others seen in this chameleon-like pair of stars?
As Haas mentions, the Reverend Webb saw greenish white and blue, so I looked up the observation on page 146 of his Celestial Objects for Small Telescopes and found other than those three words referring to the color, he had nothing else to say about 54 Leonis – which is surprising for a star as changeable as this one. But Thomas Lewis, who compiled an update of F.G. W. von Struve‘s catalog in 1906, also reported greenish white and blue. The senior Struve, by the way, left no comment whatever on 54 Leonis’ color, but the always dependable Admiral Smyth reported white and gray. And the discoverer of this pair, Sir William Herschel, described the primary as “brilliant white” and the secondary as “ash-colour, or greyish-white.” If it means anything — and at this point I doubt that it does — Admiral Smyth was using a 5.9 inch achromatic doublet refractor, while Sir William was probably using a six inch reflector with a speculum coated mirror.
So that leads us to this question: when did the yellow make its first appearance? Well actually, there was another pair of observations sandwiched between William Herschel’s and Admiral Smyth’s, which was that of Sirs John Herschel and James South in 1821 and 1822 (from their joint 1824 catalogue), and can be seen at the right. They saw yellow in the primary (as well as green in the secondary), which leaves me wondering if theirs was the only recorded 19th century observation of primarial yellow.
Could it be the predominance of yellow in our current observations is a late-20th/early 21st century phenomenon caused by too much caffeine and/or sugar? 🙄
Rather than pry further into the inscrutable physical and physiological reasons for the weird and colorful transformations of this pair of stars, for now I’ll just call whatever it is that takes takes place between them an example of stellar sleight of hand, and accept it for what it is — ravishingly beautiful and marvelously mystifying.
Meanwhile, I think I’ll just linger here in the dark a while longer and bask in the magical aura of color. Maybe if I look long enough the secondary will turn gray — or green.
And if that doesn’t happen, I’ll wander further north to our next star.
Σ 1521 (S 623) HIP: 54967 SAO: 81740
RA: 11h 15.4m Dec: +27° 34’
Magnitudes: 7.65, 8.06
Position Angle: 97° (WDS 2010)
Distance: 418 Light Years
Spectral Classification: A5
This was another pair I found in Haas’s book on the night I was raiding the cookie jar, and even though it’s also in a sparsely populated stellar region of Leo, it was easy enough to find.
Going back to the chart above (for easy reference, click here), draw a line from Zosma [Delta (δ) Leonis] to Alula Borealis [Nu (ν) Ursae Majoris] and Alula Australis [Xi (ξ) Ursae Majoris], which is a distance of about ten degrees. You’ll see the beautiful and very intriguing 72 Leonis a few degrees north of Zosma on that line, and you’ll find Σ 1521 is slightly past the halfway point between 72 Leonis and Alula Australis. With 7.60 magnitude HIP 55170 just east of Σ 1521, the two stars will be very conspicuous in your finder since there isn’t much else in the area to be seen.
Haas describes Σ 1521 as a “bright, easy, and attractively close binary” in a 125mm scope, “a pair of gloss-white stars, modestly unequal, that are split by hairs at 83x.” (page 92)
And at 109x in a 152mm refractor, that pretty well describes what I saw, although I lean toward pale white:
The first recorded observation I can find of these two stars is that of Sir James South, which was published in his 1825 catalogue as number 623. He was using a 96mm f/15.8 Dolland refractor at the time, which explains his description of the pair as very difficult when he first saw it on March 13th, 1824. He recorded a second observation a few weeks later, on April 2nd, and had a slightly easier time of it under better seeing conditions.
Again, Herr von Struve, whose catalog number is now used to designate this pair, left no description of it, but Lewis, in his 1906 compilation, reported white and greenish white. No guesses as to where the green came from, but it should be obvious by now that very strange things happen when stars are confined in a claustrophobic space. The only thing definitive about star colors is there isn’t anything definitive about star colors — but maybe this will help a little.
Meanwhile, instead of sitting here and waiting for Σ 1521 to flash me with green, I think I’ll go back to 54 Leonis and see what color it is now.