In Greek mythology, Pegasus was the flying steed created by Neptune from the blood of his wife Medusa. Perseus the Greek hero, severed the head of Medusa the Gorgon while she was sleeping. He then winged his way over land and sea holding the head of Medusa behind him. Drops of blood which fell into the sea were used by Neptune to create the famous winged horse Pegasus.
Pegasus was white as snow and gifted with immortal life and incredible speed. This winged horse was the favourite mount of Apollo and the Muses.
The first mortal to ride and tame Pegasus was the young prince Bellerophon, grandson of the King of Corinth. Flying on the back of Pegasus, Bellerophon attacked and killed Chimaera, the monster of darkness with a lions head.
Bellerophon, mounted upon Pegasus, flying through fleecy white clouds or fighting Chimaera was a favourite subject in ancient sculpture and painting.
Pegasus can be found in the northern sky near the horizon, it doesn’t rise high enough in the Southern Hemisphere to be a bright constellation for our observations therefore a dark new moon night is the best time to observe this constellation. It reaches its greatest altitude above the horizon (culmination) early in September.
The most distinguishing feature of the constellation is the “Great Square of Pegasus”. This large square is approximately 15 degrees (one and a half fists) wide in each direction. The “horse” stands upright in our sky and with some imagination appears to be flying towards the west.
The square is marked by four stars: the north-eastern corner by Alpha Andromeda (Alpheratz) which was once known as Delta Pegasi – the name Alpheratz “the navel of the horse” suggests its prior association with Pegasus. It is now considered the head of the Chained Maiden Andromeda.
In the north-western corner Beta (β) Pegasi (Scheat “the shin”) a red giant 199 ly away with a variable magnitude of 2.3 to 2.7, marks the start of two lines of stars which form the front legs of the horse.
The south-western corner is marked by Alpha (α) Pegasi (Markab “the shoulder”) a 2.5 magnitude blue-white giant star 140 ly away; and the south-eastern corner by Gamma (γ) Pegasi (Algenib, “the side”) a 2.8 magnitude blue-white pulsating variable, 333 ly away, with fluctuations too faint to see with the naked eye.
From the top left hand corner of the square a curved line of stars form the horse’s neck and head. Ending with Epsilon Pegasi also known as Enif , “the nose”, – an orange 2.4 magnitude super giant it is the brightest star in the constellation, 670 ly away. A wide 8.4 magnitude bluish companion star should be seen with small telescopes. Larger telescopes may also be able to resolve an 11 magnitude closer companion.
There are several galaxies. The brightest is NGC 7331 a 10th mag. Spiral galaxy which appears as a faint elongated streak with 10.5 cm telescope. 30 cm is required to observe the bright elongated centre. NGC 7331 is found near the border of the Constellation Lacerta – The Lizard, north of Eta (η) Pegasi.
Pi (π) Pegasi northwest of NGC 7331 is a wide binocular double, yellow and white stars of magnitude 4.3 & 5.6
Big, beautiful spiral galaxy NGC 7331 is often touted as an analog to our own Milky Way. About 50 million light-years distant in the northern constellation Pegasus, NGC 7331 was recognized early on as a spiral nebula and is actually one of the brighter galaxies not included in Charles Messier’s famous 18th century catalog. Since the galaxy’s disk is inclined to our line-of-sight, long telescopic exposures often result in an image that evokes a strong sense of depth. The effect is further enhanced in this sharp image by galaxies that lie beyond the gorgeous island universe. The background galaxies are about one tenth the apparent size of NGC 7331 and so lie roughly ten times farther away. Their close alignment on the sky with NGC 7331 occurs just by chance. Seen here through faint foreground dust clouds lingering above the plane of Milky Way, this visual grouping of galaxies is also known as the Deer Lick Group. (http://apod.nasa.gov/apod/ap140301.html)
Now the best saved for last, the most spectacular item to observe in Pegasus is M15 (NGC 7078) one of two globular clusters in the constellation, the only one worth searching for with an amateur telescope. M15 is a 6th magnitude globular cluster located a few degrees north-west of Enif, 30,000 ly away with a diameter of 12 minutes of arc. I can see a faint fuzzy haze with my 7 x 50 binoculars. With my 78mm refractor at 37x magnification with a 17mm eyepiece I see a very small circular haze. Increasing the magnification to 79 x with my 8mm Radian eyepiece a nice globular comes into view. By adding my 2x Barlow to achieve 158x the cluster is larger with a bright dense centre of stars but I was not able to resolve the stars. At least 10.5 cm telescope is recommended to resolve the stars surrounding the dense centre.
There is also a small planetary nebula within M15, NGC 7094 is an extremely difficult object to observe. It is suggested in the literature that a 30cm telescope in very good conditions will show a faint glow with a 13.6 magnitude central star. Using an OIII filter and 20cm scope it may just be visible.