By Bill Pellerin
Originally Published in the July 2016 Guidestar
Object: Three double stars
Constellation: Lyra, the Lyre (musical instrument)
Magnitude: See text
R.A.: 18 h, 50 m, 24 s (constellation)
Dec: 36° 49’ 12”
Size/Spectral: See text
Distance: 150 ly
Optics needed: Unaided eye, binoculars, and a small telescope
It’s now officially summer, as of June 20. The Sun has traveled as far north as it’s going to go this year and is beginning its long trek back south toward the winter solstice (December 21). It seems so far away now. While the hours of daylight are getting fewer now, it’ll take some time before we see significantly earlier sunsets.
Daylight saving time doesn’t help (don’t get me started on this topic). Amateur astronomers are obliged to wait later into the night (clock time) to view their favorite objects and the buzzing of the mosquitoes does not facilitate a relaxing observing session. Bug spray, anyone?
Fortunately, there are several bright objects that are worthy of your time and effort, and in this article we’ll focus on some bright stars in Vega, a constellation that is up all night in July. You should be able to find these from the city on a moonlit night, so don’t wait for ideal conditions to get the telescope out.
Let’s begin with the most recognizable star in the constellation, Vega. An A class (blue) star shining at magnitude zero means it is one of the brighter stars in the sky, fifth in order of brightness. Due to the precession of the earth’s axis it was the pole star 14,000 years ago, and if you can wait another 14,000 years or so, it will be the pole star again.
Look slightly to the east and you’ll see a small triangle of stars (no telescope needed for this). The one to the northeast is Epsilon Lyr, the famous double-double. While you may be able to see the two stars without optical aid (they’re 3.5 arc-minutes apart), you can definitely see them with binoculars. You’ll need a telescope to see that each of the stars in the pair is also a double (one of these pairs is 2.2 arc-seconds and the other is 2.8 arc-seconds). High magnification (about 200x), good seeing, good optics, and attention to the focus of the telescope are needed to see the four stars.
Delta Lyr, at the northeastern corner of the parallelogram that defines Lyra is an optical double star. The stars are just over 10 arc minutes apart and easy to see. The primary star (900 ly away) is a M class star, meaning that it’s much redder than Vega. Look to see if you can detect this color difference. Much of the radiation of this star is in the infrared, not the visible, so the total energy from this star is quite high.
Looking back in the direction of Vega, we happen upon Zeta Lyr, I measure (in TheSky software) the separation of the two stars that comprise this pair as 45 arc-seconds. You’ll need binoculars or, more likely, a telescope to split this pair. A magnification of 10 to 20 should be sufficient, and 10 power binoculars are easy to come by. You’ll need a mount to hold them steady to have a good look at the double with the binocs. (I’ve long been a fan of image stabilized binoculars. They’re expensive, but a great investment if you intend to do a lot of binocular observing.)