Astro Bob: Binocular Double Star Challenge – Can you split the sixes? – Duluth Newsstand
Sometimes it’s fun to snoop around the sky with a pair of binoculars. I did this the other night and realized there were half a dozen beautiful double stars not far from Vega, one of the brightest stars in the firmament. You may be familiar with Vega from the Summer Triangle, a giant asterism that includes Altair and Deneb that makes an appearance in the east at dusk this month.
Vega is the main luminary of the otherwise dim constellation of Lyra the Harp. We’re going to start our double star hunt here. Double stars come in two versions: actual physically connected pairs and line-of-sight pairs. In a true double, also called binary, the two suns revolve around their center of gravity. Line-of-sight pairs, called optical double stars, are unrelated but only appear close because they lie along the same line of sight. All the doubles that we will observe are physically linked except one.
Here they are:
Epsilon-1, 2 Lyre
Delta Lyra (dual optics)
Beta Lyre (Sheliak)
Naked Draconis (kuma)
Beta Cygni (Albireo)
I used a pair of no-frills 8×40 binoculars with 40mm (1.6 inch) objectives at 8x magnification. In astronomy, the objective gathers light from distant objects. It could be the shiny mirror of a reflecting telescope or the lenses at the end of your binoculars. The larger the lens, the more light it collects.
Aim for Vega and focus the star on the smallest possible point. Ready to explore? A short distance to the lower left (northeast) of Vega, you should see a nice pair of equally bright stars called Epsilon-1 and Epsilon-2 Lyrae. This physical pair is 161 light years from Earth and takes more than 400,000 years to orbit each other. How amazing that gravity makes them dance together despite being 1.6 light years apart – 100,000 times the distance between Earth and the sun.
If you have a small telescope magnifying around 100x, you will see that the two Epsilons are doubled again, making it a quadruple system. Fans long ago nicknamed this elegant quartet the double double.
A short distance (2°) almost directly below Vega you will encounter our next double, Zeta. Another true binary, it is more difficult to observe because the two stars are much closer to each other compared to Epsilon. Zeta-1 and Zeta-2 are only 44 arc seconds a part.
Two full moons placed side by side span 1°, which is equivalent to 60 minutes of arc and abbreviated 60′. Each minute of arc contains 60 seconds of arc or 60″. A single full moon measures about 30′ through or if you wish, 1 800″. This makes the separation between the two Zetas equal to 1/40 of the moon’s apparent size. It’s a narrow ribbon, but my 8x40s proved up to the task.
I could make out Zeta’s weaker companion just below, almost touching. The Zeta 1.2 pair is about 156 light-years from Earth and takes at least 47,000 years to complete an orbit.
When it comes to close doubles, it’s best to prop up your binoculars to eliminate the inevitable shake of holding them freestyle. I often lean mine against the side of the nearest building or my car for a more stable view. You can also buy an adapter to connect them to a tripod. Once stabilized, you will not only be able to split more doubles, but see more stars in general.
The next step in Lyra is the large Delta-1 and Delta-2 optical pair. Separated by 10 minutes of oceanic arc, dividing them in two was effortless. The brightest, Delta-2, is a red giant star about 900 light years away. Its reddish hue immediately caught my attention. The fainter, unrelated “companion” is nearly 200 light-years away. You may also notice a sprinkling of fainter stars around this pair. Together with Delta-2, they form the Delta Lyrae cluster.
From Delta we descend to Beta Lyrae, better known as Sheliak. The main star of this pair is actually two suns in close orbit that eclipse each other every 12.9 days. Eclipses vary Sheliak’s brightness between magnitude 3.4 and 4.1, a range wide enough to be easily noticed with the naked eye.
Beta also has an additional 7th magnitude companion far enough away to be spotted in binoculars. You’ll find it nestled 45″ below (southeast) the main star. As you did with Zeta, try supporting your binoculars for the best view.
For our last two binaries, we leave Lyra and travel to Draco and Cygnus. Nu Draconis or Kuma is one of my all time favorites. It is located about two fists above (north of) Vega in the trapezium of stars that forms the head of Draco the Dragon. The duo reminds some observers of a pair of headlights as they are close together (62″), just as bright and tight but still easy to separate. I see glowing animal eyes at night.
Our final binate gem is Albireo (Beta Cygni) located at the base of the Northern Cross. No double star grabs the attention of skywatchers more than this one, and for good reason. It’s colorful, bright, and set in a beautiful Milky Way star field. The view through a small telescope is simply spectacular.
Although much is sacrificed in the binoculars, steady hands will still split it. Separated by 35″, Albireo is a close squeaky pair, with the fainter companion shining to the left (northeast) of the main star when seen during the evening hours. Although it was a challenge in the 8x40s, I managed to separate them. I am convinced that you will have the same success.
Double stars pepper across the sky. These are some of the nicest things up there. The ones featured here will be on view all summer and fall, so you’ll have plenty of chances to see them. Let us know how you did by sharing your experience on my Astronomy for Everyone Facebook page. Good luck!
“Astro” Bob King is a freelance writer for the Duluth News Tribune.