[/caption]Summertime conjurs up great images of enjoying a double dip ice cream cone, and what more wonderful way to enjoy than with two flavors? Would you like to have some fun while the Moon waxes this coming week? Then invite someone along for the ride and let’s take a look at how differently people perceive stellar color!
Let’s begin with every one’s summer favorite – Beta Cygni (RA 19 30 43 Dec +27 57 34) – Albireo. This star is an easy and colorful split in both small telescopes and binoculars… Or is it? Well-noted for its color contrast, almost every person this author has shared the eyepiece with sees it differently. The primary star is often touted as a golden yellow and the secondary as blue…but, in whose eyes? While I perceive them as orange and almost purple, many folks have reported seeing no color at all, or radical differences between them,
Since my curiosity often runs high, I asked high noted astrophotographer, Dietmar Hager to photograph Albeiro to see what results he could capture on film. Without adding additional color correction, it appears to me to be near the orange and blue end of the spectrum. Now, let’s try a far less professional method and see what we come up with…
Although it’s on the low side, try your luck with Alpha Canes Venaticorum (RA 12 56 01 Dec +38 19 06), which is better known as Cor Caroli. The “Heart of Charles” is about 130 light-years away and is an easy double for a small telescope and even binoculars. While many very noteworthy observers fail to see color in this pair, many of us can! Take a close look… Do you think the primary star is tinged a bit more on the yellow side, while the secondary is faintly blue? Sufficiently bright enough to be caught in the act with crude methods such as a camcorder or webcam, Cor Caroli is another piece of a very cool mystery…
Now move on to Alpha Herculis (RA 17 14 38 Dec +14 23 25) – Ras Algethi – and the last player in our double-dip game. While it’s a lot tougher to split, the suggestion that the M-type primary should be red to the sight isn’t always correct. Also usually noted as a colorful pair, the companion star is supposed to be quite green – a color sensed well by the dark-adapted human eye. Perhaps some of my observing companions haven’t been quite “human,” because most see it as a very pale blue. Me? I see red and green. It would seem the answers aren’t quite black and white.
So, what do all of these stars have in common? None of them are “normal.” The A component of Cor Caroli is a magnetic and spectroscopic variable which has periodic changes in its metallic absorption lines. It is the most blue at minimum. Both the A and B stars are enveloped in an intense magnetic field. Albireo’s primary star has a composite spectrum and is actually a binary – a K-type star with a spectroscopic B-type companion. The B component of Albireo is also odd – it shows strong hydrogen absorption lines. And what of Ras Algethi? Believe it or not, the red giant primary is a variable star which is shedding a huge envelope of a gas, engulfing its B companion in the process. A companion star which itself is a binary with a composite spectrum!
Take a look at all of these stars this week before the Moon obscures their position. Albireo is the “head” of Cygnus, and Cor Caroli is the bright star located about a fistwidth away from the last star in the handle of the Big Dipper (Ursa Major). However, Alpha Herculis (south of the “Keystone”) is much more difficult to find without a starchart. For simple instructions, start at Altair (the brightest star in Aquila) and look more than a handspan west/northwest for equally bright Alpha Ophiuchi that will appear alone in the field to the unaided eye. Ras Algethi will be about 2 or 3 fingerwidths to the northwest.
Have fun and enjoy all the flavors – and colors – of summer!