How to find Albireo, Sadr, NGC 6910 & M29 in the sky on the weekend of September 27-29, 2013.
Friday, September 27 - Tonight we'll begin with an easy double star and make our way towards a more difficult one. Beautiful, bright and colorful, Beta Cygni is an excellent example of an easily split double star. As the second brightest star in the constellation of Cygnus, Albireo lies roughly in the center of the "Summer Triangle" making it a relatively simple target for even urban telescopes.
Albireo - Courtesy of John Chumack @ galacticimages.com
Albireo's primary (or brightest) star is around magnitude 4 and has a striking orange color. Its secondary (or B) star is slightly fainter at a bit less than magnitude 5, and often appears to most as blue, almost violet. The pair's wide separation of 34" makes Beta Cygni an easy split for all telescopes at modest power, and even for larger binoculars. At approximately 410 light-years away, this colorful pair shows a visual separation of about 4400 AU, or around 660 billion kilometers. As Robert Burnham, Jr. noted, "It is worth contemplating, in any case, the fact that at least 55 solar systems could be lined up, edge-to-edge, across the space that separates the components of this famous double!"
Now let's have a look at Delta Cygni. Located around 270 light-years away, Delta is known to be a more difficult binary star. Its duplicity was discovered by F. Struve in 1830, and it is a very tough test for smaller optics. Located no more than 220 AU away from the magnitude 3 parent star, the companion orbits anywhere from 300 to 540 years and is often rated as dim as 8th magnitude. If skies aren't steady enough to split it tonight, try again! Both Beta and Delta are on many challenge lists.
Saturday, September 28 - For tonight's designation, we'll have a look at the central star of the "Northern Cross" - Gamma Cygni. Also known as Sadr, this beautiful main sequence star lies at the northern edge of the "Great Rift." Surrounded by a field of nebulosity known as IC 1310, second magnitude Gamma is very slowly approaching us, but still maintains an average distance of about 750 light-years. It is here in the rich, starry fields that the great dust cloud begins its stretch toward southern Centaurus - dividing the Milky Way into two streams. The dark region extending north of Gamma towards Deneb is often referred to as the "Northern Coalsack," but its true designation is Lynds 906.
NGC 6910 - Palomar Observatory courtesy of Caltech
If you take a very close look at Sadr, you will find it has a well-separated 10th magnitude companion star, which is probably not related - yet in 1876, S. W. Burnham found that it itself is a very close double. Just to its north is NGC 6910 (Right Ascension: 20:23.1 - Declination: +40:47), a roughly 6th magnitude open cluster which displays a nice condensation of stars in a small telescope. To the west is Collinder 419, another bright gathering that is nicely concentrated.
South is Dolidze 43, a widely spaced group with two brighter stars on its southern perimeter. East is Dolidze 10, which is far richer in stars of various magnitudes and contains at least three binary systems.
Whether you use binoculars or telescopes, chances are you won't see much nebulosity in this region - but the sheer population of stars and objects in this area makes a visit with Sadr worthy of your time!
Sunday, September 29 - Tonight let's head about a fingerwidth south of Gamma Cygni to have a look at an open cluster well suited for all optics - M29 (Right Ascension: 20:23.9 - Declination: +38:3).
M29 - Hillary Mathis/NOAO/AURA/NSF
Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She has received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.