Andromeda is one of the 88 modern constellations that was likely known and named long before it appeared on Ptolemy’s list in the second century CE. But my experience is that more people associate the name Andromeda with the Milky Way’s nearest neighbor galaxy than they do the constellation. And there might be a few of you like me, who first associated the name Andromeda with “The Andromeda Strain” movie based on the Michael Crichton sci-fi thriller. But it is worthwhile to remember the constellation that predated our knowledge of galaxies and any pop culture references.
Tonight, the constellation Andromeda is in the northeastern sky right after sunset. I see it as a curved, sideways “V,” like a cornucopia spilling out to the north toward Cassiopeia. Many people find Andromeda by looking to the right and under the tilted “W” of Cassiopeia, but I usually start from the other direction with the Great Square of Pegasus. The square is at a 45-degree angle in a relatively empty part of the sky and is almost due east in the early evening. The left-most star of the square, Alpheratz, is shared between Pegasus and Andromeda, and is the tip of the V in Andromeda.
Halfway along the V and toward the W of Cassiopeia is the galaxy. At 2½ million light years away, M31 is the most distant object visible to the naked eye. But most of us can only see the bright, central core. The spiral arms seen in photographs are visible through binoculars on a dark night. They extend out so far that the entire galaxy spans the same width in the sky as six full moons.
Astronomy picture of the day
An Astronomer’s forecast for Durango
Old Fort Lewis Observatory
The star at the end of the bottom branch of the V is Almach, one of the most beautiful double stars visible with a small telescope. The brighter of the pair is a vivid gold and the other is an intense blue.
The Greco-Roman mythology surrounding Andromeda is one of the more elaborate stories and involves many characters that are now represented by various constellations in the surrounding part of the sky. Andromeda was the beautiful daughter of Cassiopeia and Cepheus (adjacent constellations) the queen and king respectively of Ethiopia. Cassiopeia claimed Andromeda was more beautiful than the Nereids (Sea Nymphs). This was a great insult, so the Nereids petitioned Poseidon to destroy the country. To appease the insult, Cepheus was ordered to sacrifice Andromeda, so she was chained to a rock by the sea to be eaten by the sea monster Cetus. Thus, she gets the name “chained woman.” Perseus, the hero of the story (and another constellation), comes to the rescue and uses the head of Medusa to get rid of the monster. He then marries Andromeda, they have lots of kids, and they all eventually get put into the sky.
The outer planets are lining up in the evening sky and are a good indicator of the ecliptic.
Saturn, to the south at magnitude 0.5 is brighter than most stars. But it pales when compared to Jupiter at magnitude -2.9. Jupiter made its closest approach to Earth last month, but is even more convenient to see this month because it is a bit higher in the sky earlier in the evening. Tonight it is near the almost-full moon.
Mars is finally rising in the late evening and has just begun its retrograde (westward) motion against the background stars as the Earth passes it in its orbit. It will reach opposition in December and will be more conveniently positioned to see after that time.
Venus had been the morning star for a while, but is very close to the sun now and will be passing behind it on the 22nd. It will reappear as the evening star next month.
The Orionids meteor shower peaks on the 21st, and will be visible after midnight for a few days both before and after the peak. Because the new moon is on the 25th, the skies might be extra dark and provide some good viewing.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory.