The Flying Horse

The horse is Pegasus, high in the southern sky, flying towards the west. The body of the horse is the Great Square of Pegasus, or autumn square. It is an almost perfect square of second-magnitude stars (as bright as those of the Big Dipper.) There is nothing quite like it in the sky; a square almost completely empty except for a scattering of very dim stars.

Pegasus head is the bright star Enif, below the square. Why he is upside down is neatly answered by a Greek myth (there was an answer for everything.) The hero Bellerophon, riding Pegasus, tried to storm Mt. Olympus. Enraged, Zeus sent a horsefly to sting Pegasus, who turned over, dropping Bellerophon into the sea.

The four stars of his body and the one of his head are equal in brightness, but not in temperature. Enif and the right (western) star of the square are both very cool, only about half as hot as the Sun. Consequently, they both appear red-orange, especially when compared with the blue-white of the other stars.

Near Enif is the spectacular globular cluster M15, a compact ball of hundreds of thousands stars. This is one of the finest globular clusters visible through binoculars. To find M15, face north, put Enif on the left (east) of your field of view and move the binoculars slightly to the right (west.) It will look like a hazy spot of light.

A constant stream of X-rays comes from M15. One of the stars in M15 was double, and one of the two has burned out. The corpse of this massive star has become a black hole, and we receive no light, no radiation of any sort from this hole. But gasses from its companion flow towards the hole, are heated by friction, and emit X-rays.

(10/22/08)