Pegasus

The fall/winter Horse with a great cluster at the reins and Andromeda hanging on.

Pegasus … and You


Credit: John Flamsteed, 1646-1719. Public Domain


Pegasus …

Constellation Pegasus has been recognized as a horse by civilizations as early as Mesopotamian. It’s a curious fact since the horse is upside down and has indistinct hind portions. The alpha star can be seen at the front of the wing in the Flamsteed illustration above. Gamma Peg is further back in the wing and beta is at the start of the graceful forelegs. They are three corners of the Great Square.


The neighborhood picture below will show how to reach Pegasus from constellation Cygnus, as well as from Cassiopeia to the north. and Capricorn in the south. Pegasus, high overhead in November evenings, is easily recognized by the Great Square denoting its body proper. It is the seventh largest constellation and in ancient times may have been even larger before portions were co-opted by others in the zodiac. Leaving the western corners of the Square are the star trails that suggest to me the neck and head below and the forelegs above. The neck trail takes a bend northward suggesting the head and nose of the horse.


Interactive Sky Chart from Sky & Telescope


The one not to miss. The “nose” star is Enif, and using binoculars you can extend this trail west and north 4 degrees to an object of great interest. The star cluster M15 has been admired for centuries for its enchanting appearance, and in recent decades has revealed important scientific information.


First, the aesthetics: binoculars may show it as a fuzzy patch; a small telescope will resolve a cluster almost as bright and populous as M13, the finest cluster in the northern celestial hemisphere. Despite being out-glitzed, M15 is my personal favorite because of its distribution pattern. A smattering of resolvable individual stars invites you inward to a dense cauldron of possibly a half-million stars.


Next, the science: Burnham, in the 70s reported that the cluster was found to be a source of X-ray energy. He noted theories about the possibility of supernova remnants or even a black hole – “so popular with writers on speculative cosmology.” Is a black hole in M15 still a speculation? [See Projects below.] With modern instruments scientists have detected even variable stars and a planetary nebula in the mix, but there has been a much more recent development. In 1995 Swiss astronomers Michel Mayor and Didier Queloz announced that they had detected for the first time a planet outside of our solar system. The planet orbits the star 51 Pegasus which resides very near the western edge of the Square. I was new to astronomy, my newly acquired hobby, and this news shook the ground under my feet. Since then many other exoplanets have been detected.


M15. Credit: ESA/Hubble & NASA


Following the chart above eastward, we see that even a corner of the Great Square has been assigned to constellation Andromeda, a maneuver that probably springs from the myth of the Perseus rescue of the damsel in distress and her holding onto Pegasus for dear life. More on this sector below.


Sources: Burnham’s Celestial Handbook and the Audubon Guide to the Night Sky.


… and You

1. Use your extended arm and hand as a gauge to measure in degrees the width and height of the Great Square. You might recall from an activity in the Ursa Major article that the bottom of the Dipper bowl is about 10 degrees.


2. Has a black hole been confirmed to reside in the cluster M15? Look here.


3. Using the chart above, you can trace a trail from the northeast [Andromeda] corner of the Square. Outside with binoculars or just your eyes, follow the trail past a minor star to bright beta. Look either side of beta and you should see M31, The Andromeda Galaxy, a near twin of our Milky Way. On the other side of beta is a faint spiral galaxy M33 available only in a telescope.


4. The next bright star along the Andromeda trail is gamma and a small telescope should show it as a double star of beautifully contrasting colors. As others have, you can form your own opinion as to what the colors are.


5. The star 51 Pegasus hosts what type of planet? Could there be life on it?


6. About those myths. You can search for and read about the perils of Andromeda and her rescue by Perseus atop the steed Pegasus. There is also an older – some say more authentic – myth about the horse’s origin and his rider Bellerophon. What’s confusing to me is that that monster called Gorgon Medusa seems to be involved in both myths. Can you sort it all out?