Astro Bob: Binocular double star challenge — can you split all 6?
Grab your binoculars for a look at these six attractive double stars all located near the bright star Vega.
Sometimes it's fun to poke around the sky with a pair of binoculars. I did that the other night and realized there are a half-dozen nice double stars not far from Vega, one of the brightest stars in the firmament. You might know Vega from the Summer Triangle, a giant asterism that includes Altair and Deneb that makes its appearance in the east at nightfall this month.
Vega is the head luminary in the otherwise faint constellation Lyra the Harp . We'll begin our double star hunt here. Double stars come in two flavors: real, physically connected pairs and line-of-sight pairs. In a true double, also called a binary, the two suns revolve about their center of gravity. Line-of-sight pairs, known as optical double stars, aren't related but only appear close because they lie along the same line of sight. All the doubles we'll observe are physically bound except one.
Here they are:
Epsilon-1, 2 Lyrae
Delta Lyrae (optical double)
Beta Lyrae (Sheliak)
Nu Draconis (Kuma)
Beta Cygni (Albireo)
I used a pair of nothing-fancy 8x40 binoculars with 40-millimeter objectives (1.6 inches) that magnified eight times. In astronomy, the objective gathers the light of distant objects. That can be the shiny mirror in a reflecting telescope or the lenses at the end of your binoculars. The bigger the objective the more light it collects.
Aim at Vega and focus the star down to the smallest point you can. Ready to explore? Just a short distance to the lower left (northeast) of Vega you should see a neat pair of equally bright stars called Epsilon-1 and Epsilon-2 Lyrae. This physical pair lies 161 light-years from Earth and takes more than 400,000 years to complete an orbit about each other. How amazing that gravity keeps them dancing together despite their separation of 1.6 light-years — 100,000 times the distance between the Earth and sun.
If you have a small telescope magnifying around 100x you'll see that both Epsilons are double again, making them a quadruple system. Amateurs long ago nicknamed this elegant foursome the "Double-Double."
A short distance (2 degrees) almost directly below Vega you'll encounter our next double, Zeta. Another true binary, it's more challenging to observe because the two stars nestle much closer together compared to Epsilon. Zeta-1 and Zeta-2 lie just 44 arcseconds apart.
Two full moons placed side by side span 1 degrees, which is equal to 60 minutes of arc and abbreviated as 60 feet. Each arc-minute contains 60 arcs-seconds, or 60 inches. A single full moon measures about 30′ across or if you like, 1,800 inches. That makes the separation between the two Zetas equal to 1/40 the apparent size of the moon. That's a narrow sliver, but my 8x40s proved up to the task.
I was able to make out Zeta's fainter companion directly below it, almost touching. The Zeta 1,2 pair lies 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 support your binoculars to eliminate the inevitable shake from holding them freestyle. I often buttress mine against the side of the nearest building or my car for a steadier view. You can also buy an adapter to connect them to a tripod. Once stabilized you'll not only be able to split more doubles but see more stars in general.
Next up in Lyra is the wide, optical pair Delta-1 and Delta-2. Separated by an oceanic 10 arc-minutes, splitting them in two was effortless. The brighter, Delta-2, is a red giant star about 900 light-years distant. Its reddish hue immediately caught my eye. The fainter, unrelated "companion" lies almost 200 light-years farther away. You may also notice a sprinkle of fainter stars around this pair. Along with Delta-2 they form the Delta Lyrae Cluster .
From Delta we drop down to Beta Lyrae, better known as Sheliak . The main star in this pair is really two closely-orbiting suns that mutually eclipse each other every 12.9 days. The eclipses cause Sheliak's brightness to vary between magnitude 3.4 and 4.1, a spread large enough to easily detect with the naked eye. Following the star's ups and down may be something you'd like to add to your astro to-do list.
Beta also has an additional companions including a seventh magnitude star far enough away to spot in binoculars. You'll find it tucked close 45 inches below (southeast) the primary star. Since seventh magnitude is on the faint side you'll need a steady hand and a dark night to spot this one. Of the six, this will be the most challenging.
For our final two binaries we leave Lyra and travel to Draco and Cygnus. Nu Draconis or Kuma is one of my all-time favorites. It's located about two fists above (north of) Vega in the trapezoid of stars that forms the head of Draco the Dragon . The duo reminds some observers of a pair of headlights because they're close (62 inches), equally 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 gets more attention from sky watchers than this one and for good reason. It's colorful, bright and set in a glorious field of Milky Way stars. The view through a small telescope is nothing short of spectacular.
While much is sacrificed in binoculars steady hands will split it just the same. Separated by 35 inches, Albireo's a squeaky close pair, with the fainter companion shining to the left (northeast) of the main star when viewed during the evening hours. Although a test in the 8x40s I succeeded in prying them apart. I'm confident you'll have the same success.
Double stars pepper one end of the sky to the other. They're some of the prettiest things up there. The featured ones here will be visible all summer and fall, so you'll have lots of chances to see them. Let us know how you fared 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.