Friday, July 16
By the time the sky grows dark after sunset, the constellation Lyra is already high in the east. The Harp is home to the famous Double-Double: A naked-eye double star in which each bright sun has a second companion.
Start at Vega, Lyra’s unmistakable magnitude 0 alpha star. From there, swing your gaze 1.7° east-northeast, where you’ll find a close pair of magnitude 4.6 stars. They’re separated by 3.5′ (or 208″), which is just about the limit of naked-eye resolution for most people. Can you see the two distinct stars? The luminary to the north is Epsilon1 (ϵ1) Lyrae, while the other is Epsilon2 Lyrae. Even if you can’t separate them by eye, virtually any pair of binoculars or a small telescope will split them.
Once you zoom in on the pair, bump up the magnification to at least 80x and you’ll see that both Epsilon1 and Epsilon2 have a companion. This is why they’re called the Double-Double. The components of Epislon1 are separated by 2.8″; Epsilon2 is separated by 2.2″. Although the entire system is gravitationally bound for now, ultimately the pairs of Epsilon1 and Epsilon2 may go their separate ways.
Sunrise: 5:45 A.M.
Sunset: 8:27 P.M.
Moonrise: 12:32 P.M.
Moonset: 12:03 A.M.
Moon Phase: Waxing crescent (42%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 12 P.M. local time from the same location.