The Ethiopian Princess and Her City of Stars
She is the headliner of our Dark Skies Stargazing Night and she is coming to a galaxy near you!
On Friday, January 27, from 7 pm to 11 pm at Camp Umoja’s Campground, get an up close and personal look through a telescope at the sparkling city of the Ethiopian Princess, Andromeda.
January night sky from Mandahl Beach, Orion ascending. ©karlcallwood
The Great Andromeda Galaxy: a City of Stars
By Richard Callwood
The Great Andromeda Galaxy, also known as M31, is a giant spiral galaxy, much like our own Milky Way Galaxy. It is the nearest spiral galaxy to our own, “only” 2.5 million light years away.
That means that it takes 2.5 million years for light from M31 to get to Earth. Great Andromeda is the largest galaxy in our Local Group of galaxies, with approximately 1 trillion stars. The Milky Way is the second largest.
The galaxy is named for the constellation Andromeda, who, in Greek mythology, is a princess of Ethiopia.
It is called M31 because it is the 31st entry in a catalog of objects that might be mistaken for comets, compiled by 18th century French comet hunter Charles Messier.
On a dark night, M31 can be seen with the naked eye.
The Milky Way and M31 are approaching each other. The startling 1912 discovery that M31 is rapidly closing on us raised the question of how far away it is. It is estimated that in several billion years, the two galaxies will collide, and perhaps merge. Not to worry, though: stars are spaced so far apart from each other that there is almost no chance that a star from M31 will collide with the Sun.
Orion descending west over Mandahl. ©karlcallwood
The Great Andromeda Galaxy has played an important role in showing us the size of the universe.
Prior to the 20th century, it was believed that the Milky Way was the only galaxy in the universe. Before the invention of astrophotography, it was unknown whether M31 was a cloud of gas or a cluster of stars. Indeed, it used to be known as the Great Andromeda Nebula. Even through the most powerful telescopes, the human eye cannot discern individual stars in M31. But astrophotography proved that M31 is made of stars.
Early in the 20th century, astronomer Henrietta Leavitt discovered a way to determine the distance to a certain class of stars called Cepheid variables (named after the constellation Cepheus, the king of Ethiopia). In 1925, Edwin Hubble, after whom the space telescope was named, used Cepheid variable stars in M31 to prove conclusively that M31 is far outside the Milky Way, and is in fact another galaxy. Scientists immediately realized that the thousands of similar objects in the sky were also galaxies, but much farther away.
The universe turned out to be much larger than anyone had imagined.
###
