By Peter Becker
Equestrian lovers may put their horse in the barn for the night, but the sky above has a number of these noble animals trotting across. I say trotting relatively speaking, since all constellations move around the whole sky only once in 24 hours.
We have in the autumn the interesting and huge constellation Pegasus, the Flying Horse. This is marked especially by the "Great Square of Pegasus," more of a rectangle, riding up in the east on September or evenings. Most star charts show the constellation Andromeda attached to Pegasus. The configuration of both these star groups easily outline an entire horse, though as seen from the Northern Hemisphere, this horse figure is riding upside down.
In addition to Pegasus, just ahead of this constellation is a very small and faint group, Equuleus, the Little Horse.
The lead star in Pegasus- the one farthest west- is fairly conspicuous and is known as Enif.
Equuleus contains an interesting ring of stars, visible in a small telescope. This "ring" is actually an asterism- a chance grouping of stars not officially designated as a constellation. The Great Square of Pegasus is also an asterism, being formed from two constellations, Andromeda and Pegasus.
Speaking of asterisms and horses, look low in the north-northwest for the Big Dipper. This most famous grouping of stars is part of a larger constellation, Ursa Major the Great Bear. The dipper portion is referred to as an asterism. So where’s the horse? The middle star of the handle- the one that’s "out of line" with the rest, is sometimes called the Horse. Look very carefully. With unaided eyes you should see a fainter star right next to the "Horse." This one is called the Rider.
The Horse and Rider trot around the North Star in an unending circle, every night and day-. Their riding track does not end when the Sun comes up; even in broad daylight, they are there, in the northern sky, trotting around in their celestial circuit, though invisible until soon after the Sun sets again. These stars are also named Mizar (the brighter one) and Alcor. They are a chance pairing of stars on the sky and not an actual double star, If you have a telescope, be sure to look at Mizar. You will find it is split into two stars, an actual double star tied together by their mutual gravity and waltzing through space as one.
You may have seen pictures of the Horsehead Nebula. You need a very large telescope and an excellent night to detect it, but long exposure photographs show it best. Situated in the winter evening constellation Orion, the Horsehead is an expanse of cosmic dust, seen in silhouette in front of a more distant nebula made visible by reflected starlight. By pure chance, or perhaps a heavenly gift for horse lovers who look up, the dark nebula strikingly resembles a horse’s head, with its snout and flowing mane.
First quarter Moon is on Thursday, September 12.
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Keep looking up!