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Locating the Great Galaxy in Andromeda

Locating the Great Galaxy in Andromeda

Many astronomy textbooks say that September is the best time to locate the star constellation Cassiopeia and its neighboring galaxy in Andromeda. This “nearby” spiral galaxy is approximately 2.5 million light-years from Earth and is the farthest object you can easily see with your eye at night.

While you are showing your friends how to spot both on a dark starry night, you can recount the tale of Cassiopeia’s “throne in the sky” and the ordeal her daughter went through because she was quite attractive. The story is of course a Greek myth but it goes like this:

Cepheus, King of Ethiopia, was married to Cassiopeia and she bore him a daughter they named Andromeda. Unfortunately, mom was terribly boastful of her daughter’s beauty. Cassiopeia even claimed that Andromeda was even prettier than the Sea Nymphs who didn’t take that too kindly and in a quickly assembled group protested to Poseidon, god of the sea.

Now, Poseidon, being mindful of his position and always happy to be in good favor with the Sea Nymphs, agreed to punish Cassiopeia for her bragging about her daughter. He sent the sea monster Cetus to ravage the coast of Ethiopia and all structures along it. King Cepheus, hearing of the destruction consulted a wise man as to how to stop this monster from wreaking havoc on the population.

He was advised that the only way to stop the devastation was to sacrifice his daughter Andromeda to the monster. Being a good king and father he was torn between the love for his people and the love for his daughter. Wanting to remain popular with the rank and file, he made a decision and chained his daughter Andromeda to a rock by the sea and ran away.

But as the monster Cetus approached the doomed girl, down from the sky comes the hero Perseus flying on who else but Pegasus the horse! It only took one look for Perseus to be smitten by the beauty of Andromeda. He quickly slew Cetus and claimed the hand of Andromeda. According to mythology they lived a happy long life and were given places in the night time sky to reside forever as a stellar reward.

In early September Cassiopeia is easy to spot since it is almost overhead and looks like a big W in the night sky that is supposed to represent Cassiopeia’s throne. Once you have found this, look south to Pegasus and east to see Perseus and his love Andromedia who are close enough to be holding hands.

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The brightest star in Cassiopeia is Schedar located at one of the two points of the W. The name means “breast” in Arabian. Another prominent star, Ruchbah, means “knee” and shows that the queen is sitting in her chair.

Midway along the arm of the throne was once a strange object called Tycho’s Star that has disappeared over the years. First seen on the night of November 11, 1572 by the great astronomer Tycho Brahe, it was a supernova explosion rather close to our Earth and it was so bright it could even be seen in the daytime. Within two weeks its luminosity began to fade and change color, from bright white over to yellow and orange and finally to a faint reddish point. In a year and a half it was gone. The remnant of the supernova was not found until 1952 with the aid of the Mount Palomar telescope.

So how can you spot the galaxy in Andromeda? That is an easy thing to do. Locate the prominent Cassiopeia, the Big W which is sideways this time of year. Use the top V of the W as a pointer, let your eye head east about a hand’s width (hold it up) to a smudgy object that is not a star and there it is.

What you are really seeing is only the brighter central region of the galaxy that holds over a trillion stars densely packed. If the entire extent of the galaxy were visible to your eye, it would span a distance six times as large as a full Moon.

The fact that it takes light 2.5 million years to reach us here on Earth from Andromeda means that the particles of light hitting your eyes started out long before humans walked our planet. According to history, the earliest recorded observation of the Andromeda Galaxy was in 964 AD by a Persian astronomer, Al-Sufi, who described it as a “small cloud” in his Book of Fixed Stars. The first telescopic observation was given by Simon Marius in 1612, and Charles Messier catalogued it as object M31 in 1764 in his catalog of nebulous objects.

In 1785, the astronomer William Herschel, discoverer of the planet Uranus, noted a faint reddish hue in the core region of the galaxy but it wasn’t until 1887 when the first photographs of the galaxy were taken by Isaac Roberts that astronomers realized it was spiral shaped much like our own Milky Way galaxy where we reside.

For those who need something to worry about, it seems that the Andromeda Galaxy is actually heading straight towards our Sun with a velocity of about 60 miles per second and will hit us someday in the future. When this happens in 2.5 billion years astronomers believe that they will form a giant elliptical mega-galaxy – perhaps the largest around.

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Gary Hanington is Professor Emeritus of physical science at Great Basin College and chief scientist at AHV. He can be reached at: garyh@ahv.com or gary.hanington@gbcnv.edu.

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