Pegasus is a large, northern constellation bordered by Pisces, Cygnus, and Andromeda. It is best seen in the Northern Hemisphere from August to October.
History and Mythology
The name Pegasus means 'Springs of Ocean'. It was the mythical winged horse of Bellerophon. This is a snowy white creature with a golden mane that runs across the sky with his head pointed toward the equator. Pegasus was born from the blood of the monster Medusa, who was slain by Perseus. Drops of Medusa's blood fell into the ocean, and mixed with sea foam, creating the winged horse. Pegasus was the favorite of the Muses, because his hoof marks caused the fountain of inspiration to start flowing. It was believed that Pegasus was found by Bellerophon drinking at this fountain.
Bellerophon was a young man who had been sent to slay a fire-breathing monster with the head of a lion, the body of a goat, and the tail of a dragon. Pegasus helped him kill the monster. Bellerophon tried to ride Pegasus into the heavens, but the gods sent an insect to sting Pegasus and throw his rider. Bellerophon was doomed to spend the rest of his life on earth wandering about, blind and lame. Pegasus flew into the heavens, where he became the thundering horse of Zeus, and carried divine lighting.
Notable Stars
Pegasus is the centerpiece of the autumn sky for northern observers. Four stars form the famous Great Square of Pegasus. One of these stars, Alpheratz, is actually part of the constellation Andromeda. The brightest star in Pegaus is actually Epsilon Pegasi or Enif, whose traditional arabic name means "the mane". It is a cool orange supergiant 670 light years distant.
The 2nd-brightest star in Pegasus is Beta Pegasi or Scheat, whose name means shoulder, and it is a red giant varying in magnitude from 2.4 to 2.8. Markab, or Alpha Pegasi, is the third star in the Great Square, at magnitude 2.5. The fourth star in the Great Square is third-magnitude Algenib, or Gamma Pegasi.
51 Pegasi was the first sunlike star found to have a planet orbiting it. It is a 5.5 magnitude star 50 light years away. The exoplanet's discovery was announced in 1995. It is contains half the mass of Jupiter and orbits 51 Pegasi every 4.2 days, a 1/20th the distance from the Earth to the Sun. The discovery of this "hot Jupiter" and many others like it around other stars forced astronomers to rethink their theories of planetary formation and evolution.
Clusters, Nebulae, and Galaxies
M 15 is a bright globular cluster of 6th magnitude. It is about 33,000 light-years away and can be seen with binoculars. It is easily viewed in an 8 inch telescope. This cluster emits X-rays, which may be produced by a black hole at its center.
In northwestern Pegasus is the impressive spiral galaxy NGC 7331. This galaxy is highly inclined from our point of view, and is about 50 million light-years away. Under good sky conditions, a 10 to 12 inch telescope reveals the spiral arms in NGC 7331. This galaxy is probably similar to the Milky Way.
Pegasus contains a very unusual group of five interacting galaxies known as Stephan's Quintet. Stephan's Quintet is an apparent cluster of galaxies whose members have widely varying red shifts, and hence very different distances. Yet these galaxies appear to be connected each other by faint tendrils of material. This puzzle is unresolved.
For larger telescope, NGC 7479 is a barred spiral galaxy in Pegasus of about 11th magnitude, and is about 105 million light-years away. NGC 7814 is an edge-on spiral galaxy at a distance of about 40 million light-years.