Pegasus is a beautiful, handy July-to-January constellation (Northern Hemisphere) which you can use to locate other stars, constellations, and objects in the night sky. The rest of the time it lies below the horizon in the northern hemisphere.
Seventh Largest Constellation
Pegasus is the seventh largest constellation, taking up nearly 1,200 square degrees of space in the night sky, and can be seen by observers located between +90° and -60° of latitude. Another way to locate it is to find the “pointer stars” in the Big Dipper and follow an imaginary line running through them and Polaris over to Cassiopeia and then onto Pegasus.
Brightest Stars of Nearly Equal Magnitude
The constellation sits in an area of the sky that is chiefly populated by dimmer stars, but it has three reasonably bright stars, which are of nearly equal brightness.
-Enif (Epsilon Pegasi), the brightest star in Pegasus, is an orange super-giant (K2 Ib) located 690 light years away with a visual magnitude of 2.399. It has 12 times our sun’s mass, 185 times its radius, and is 5,000 times more luminous. Enif means “the nose” in Arabic and marks the muzzle of the Winged Horse.
– Scheat (Beta Pegasi), the second brightest star in Pegasus, is a red giant star (M2.5II–IIIe) found 196 light years from our solar system. It shines with a magnitude of 2.42, although being a semi-regular variable this can vary from 2.31 to 2.74. Scheat has around twice the Sun’s mass, and 1500 times its luminosity. The name Scheat derives from the Arabic for “the upper arm.”
– Markab (Alpha Pegasi), the constellation’s third brightest star, is a blue giant situated 133 light years distant of magnitude 2.48. It has nearly five times the radius of the Sun, and is 205 times more luminous. Markab derives from the Arabic for “the saddle of the horse”.
Of the many stars in Pegasus, eight are known to have planets of their own. In fact other than our Sun, 51 Pegasi was the first main-sequence star discovered with a planet.
The Great Square of Pegasus Asterism
The familiar asterism known as the Great Square of Pegasus consists of the three brightest stars in the constellation of Pegasus, and Alpheratz (Alpha Andromedae), the brightest star in the constellation of Andromeda. This hot blue star has a visual magnitude of 2.07, making all the four stars which make up the Winged Horse’s body of 2nd magnitude. The Great Square lives up to its name, with each side around 15 degrees in length, meaning its easy to find, and a useful marker for identifying a number of other constellations.
Named After Mythological Winged Horse
Pegasus was mentioned by the Ptolemy in the second century, and is one of the original 48 constellations that he wrote down in his astronomical treatise called Almagest. Of course it got its name from the famed winged-horse from Greek mythology, who was born after Perseus beheaded the gorgon Medusa and her blood mixed with seawater to create the fabulous creature. Pegasus was mortal, though, but because of its lifelong service to Perseus and Andromeda, on the last day of its life he was made into a constellation.
Useful In Locating Andromeda Galaxy
If you drew an imaginary line through Alpheratz and past Markab for a distance about three-quarters the width of the Great Square, you will find the Andromeda Galaxy. Earth’s closest spiral galaxy sits a little more than 2.5 million light years from Earth, and is structured very similarly to our own Milky Way. In the same way that you cannot get a good look at the outside of your car when you’re sitting in it, we can’t get a good look at our own galaxy because we’re within it. That’s why it’s interesting to study one that is built similarly to our own. Well that and the fact that it’s on a direct collision course with our galaxy… (Don’t panic… it won’t happen for 4 billion years.)
The Andromeda Galaxy (M31) has an apparent visual magnitude of 3.4, making it the second brightest Messier object behind the Pleiades (M45), which is of magnitude 1.6. The Andromeda Galaxy has more than a trillion stars, while the Milky Way galaxy pales in comparison with between 200 and 400 billion stars.
Contains One Of Oldest Globular Clusters
In this constellation can be found Messier 15 (M15), which at around 12 billion years old is one of the oldest globular clusters ever discovered. It is situated 33,600 light-years away, is around 175 light years wide, and contains more than 100,000 stars, including variable stars, pulsars and a double neutron star system, as well as a planetary nebula.
Rich In Galaxies
Provided you look deeply enough in any part of the sky you’ll see thousands upon thousands of galaxies; and Pegasus has quite a number that aren’t too far away. The constellation has a preponderance of named galaxies in it, many of which have NGC numbers (New Galactic Catalogue). These include NGC 1 (the very first entry in the NGC), 7479, 7814, 23, 7673, 7217, 7331, 7742, 7315, 7078, 7725, 7753, and galaxies 7317-7320, also known as Stephan’s Quintet.
As you may know, there are around 100 billion galaxies in the observable universe and 70 sextillion stars (70,000,000,000,000,000,000,000). The Sloan Digital Sky Survey (SDSS) has mapped a paltry 400,000 galaxies out of that number. To put the survey into perspective, remember that each one of the disks seen in SDSS image is a galaxy similar to our own, and it would take 30,000 to 120,000 years for light to cross each individual fuzzy patch.
Contains Einstein’s Cross
But even if Pegasus is rich in galaxies it has one thing that nobody else has: Einstein’s Cross! What you’re seeing here is a visual anomaly caused by gravity. In the center of the image is the galaxy NGC 7331; surrounding it are four identical quasars. Except that there’s actually only one – the same one – which is directly behind the galaxy from our point of view, so the gravity of the galaxy is bending the light of a single quasar around it on four different sides. If it wasn’t for this “gravitational lensing” we wouldn’t even be able to see that quasar. The galaxy itself is only 38 million light-years away, however the quasar behind it, one of the older objects in the universe, is eight billion light years away and much brighter than the galaxy. Intriguing, no?
Home To The Pegasids Meteor Shower
In any event, Pegasus can lay claim to one meteor shower, the Pegasids which occurs every year between 7th and 13th July, but it’s typically a weak shower which only produces around three meteors per hour. They are very fast, though, in the order of 45 miles per second (70 k/s) but in general the debris entering Earth’s atmosphere is very small, and no more than the size of a grain of sand.