October evenings offer Michigan sky watchers a naked-eye view of a galaxy more than two million light-years away and a fine vista of the Great Square in the constellation of Pegasus, the Flying Horse of Greek mythology, according to astronomer Richard G. Teske.
The body of the horse is outlined by the four stars of the Great Square. As seen from Michigan, Pegasus flies on his back, his faint wings extending downward to the south. His nose points toward Aquila in the west, marked by the star Enif, “The Nose.”
The Great Square in Pegasus includes an unusual example of a single star being shared by two constellations, Teske explains. At the northeast of the Square is Alpheratz, a star originally assigned to Pegasus that ended up in Andromeda when constellation boundaries were officially defined by the International Astronomical Union in 1930. In ancient legend, Andromeda was the daughter of Queen Casseopeia, who has her own constellation in the northern sky.
If you’ve ever wondered how far you can see with your unaided eyes, Teske suggests you look toward Andromeda during October or November for the spiral galaxy that astronomers call M 31.
“Choose a clear night when the moon is not lighting up the sky very much, and observe from a dark location away from city lights,” Teske says. “After finding Alpheratz in the northeast of the Great Square, let your eyes travel further to the northeast for two stars and then look north toward the faint fuzzy patch of the galaxy. Binoculars will be helpful, but are not necessary. When you locate M 31, you will be looking at the most distant object visible without a telescope—two and one-half million light-years from Earth.”
According to Teske, M 31’s pale light comes from millions of stars that reside in the central bulge of the galaxy, each of them a thousand or more times brighter than the sun. “Long exposure photographs show the galaxy actually stretches the width of three full moons across the sky. But your eye by itself is only able to pick out the bright inner bulge where most of the stars are located, and cannot see the faint spiral arms around it,” Teske says.
If you use binoculars or a small telescope, Teske suggests using only low magnification to see the galaxy’s central bulge at its best. Even a large telescope will not reveal all the details a photograph can show.
“M 31 in Andromeda is the largest and brightest of about 24 galaxies that are companions to the one in which we are located. The whole group of them is flung across almost three million light-years of space.” he notes.
“Astronomers believe that our local group of galaxies is held together by the mutual gravitational attraction of all 20-some members, despite its vast size,” Teske explains. “Sky watchers viewing M 31 will not feel its gravitational pull, but nevertheless the pull is there. All the stars in our galaxy respond weakly to the perpetual beckoning of M 31. As a result, the two galaxies perform a slow orbital dance about one another that takes billions of years to complete.”
