Double star observing is fun, easy and best of all, it can be done under less than ideal conditions of light pollution, moon light and even telescope size. Below is a fun list (with a challenge or two) to get you started. Make it even more fun and hone your observing skills by drawing what you see in a simple double star observing log. Just note the name of the double star system, the constellation, coordinates, the conditions, date, time, telescope used and within a small circle, place two dots on what you see through your telescope (or even binoculars).
One form that you can use is found at: https://www.astroleague.org/al/obsclubs/dblstar/dblstarl.pdf
alpha1, alpha2 Capricorni (alpha1, magnitudes 4.2 and 9.2, separation 45.4 arcseconds; alpha2, mags 3.6 and 9.3, sep 154.6”) The magnitude 4.2 (alpha1) and 3.6 (alpha2) stars form a naked eye pair separated by 376”. A 3-inch scope will capture their 9th magnitude companions.
20h 18m 10.5s
-12° 28′ 49″
gamma Delphini (mags 4.5 and 5.5, sep 9.6”) The Dolphin’s “snout.” One of the finest double stars for small-aperture telescopes. Can you detect the pair’s subtle yellow and blue colors? If you would like a bit of a challenge, can you find n the same field, ¼ degree to the southwest, is the delicate little pair Struve 2725 (mags 7.6 and 8.4, sep 5.8”)
20h 47m 05.1s
+16° 09′ 16″
61 Cygni (mags 5.2 and 6.0, sep 30.5”) This binary pair is historically important as the first star whose distance was accurately determined (Bessel – 1838). Both stars appear golden yellow.
21h 07m 20.1s
+38° 46′ 59″
Struve 2816 and Struve 2819 Cephei (Struve 2816, mags 5.6, 7.7, and 7.8, sep 11.7” and 19.9”; Struve 2819, mags 7.5 and 8.5, sep 12.4”) A triple star and double star in the same low-power field. This is a very interesting and wonderful sight.
21h 39m 13.0s
+57° 31′ 54″
epsilon Pegasi (mags 2.4 and 8.4, sep 142.5”) An optical, or line-of-sight, double. What makes this pair so interesting is the apparent pendulum-like motion of the fainter star when the telescope is gently rocked in a direction perpendicular to a line connecting the two stars.
21h 44m 38.6s
+09° 54′ 56″
zeta aquarii (mags 4.3 and 4.5, sep 2.2”) A beautiful twin binary that is slowly widening from a minimum separation of 1.7” in 1977. Use at least 100X for a comfortable split.
22h 29m 18.6s
+00° 01′ 35″
sigma Cassiopeiae (mags 5.0 and 7.1, sep 3.0”) A tough “split” for small scopes, because of the two-magnitude difference in magnitude of the component stars. Just one degree north is the remarkably rich open star cluster NGC 7789.
23h 59m 27.3s
+55° 48′ 18″
eta Cassiopeiae (mags 3.4 and 7.5, sep 13.0”) What makes this slow-moving binary pair (period = 480 years) noteworthy is its color scheme – yellow for the primary star, red for the companion. Marginally visible in small instruments, the colors really stand out in a 6-inch scope. It is a favorite.
00h 49m 37.8s
+57° 51′ 50″
alpha Ursae Minoris (mags 2.0 and 9.0, sep 18.4”) Polaris, the North Star. This is a classic light test for the common 60mm refractor. The 9th magnitude companion is hard to spot in the glare of the bright primary star. Easy in a 6-inch scope; shows yellow and blue colors.
02h 41m 24.8s
+89° 18′ 23″
gamma Arietis (mags 4.8 and 4.8, sep 7.8”) A grand “twin” pair, both white. Their telescopic appearance look like a pair of glowing eyes.
01h 54m 01.9s
+19° 20′ 29″
Authored by Stacy Jo McDermott.
Stacy Jo McDermott is an amateur astronomer living in Oakland, CA surrounded by street lights. She’s been enjoying the hobby of astronomy since 1999. Double stars have been providing the bulk of the party at the eye piece. Questions and suggestions on turning off street lights can be sent to email@example.com