D e s e r t E x p o s u r e 
january 2005
D e s e r t E x p o s u r e |
|
The Starry Dome
by Bert Stevens This month's constellation is not a warrior or a doer of great deeds, but a princess who kept a promise. Andromeda is a member of the royal family of the ancient kingdom of Aethiopia (not in present day Ethiopia, but Israel). Most of this royal family and the other characters in this story have ended up as constellations in our sky.
The king at the time was Cepheus. He had journeyed with Jason and the Argonauts in search of the Golden Fleece. After his adventures, he settled down as the King of Aethiopia. He married the beautiful, but vain, Cassiopeia. Soon after their marriage, Queen Cassiopeia presented her husband with a daughter, Princess Andromeda. Andromeda inherited her mother's beauty. Cassiopeia was very proud, and boasted that she was more beautiful even than Nereids, a sea nymph. When Nereids overheard her boasting, she became very jealous and went to Poseidon, god of the Sea, who sent Cetus, the sea monster, to lay waste to the coast of Aethiopia, kill its people and cattle. Cetus attacked in the form of a huge whale. King Cepheus, wanting to stop the slaughter, consulted an oracle, who told him to offer his daughter to the sea monster, and this would appease Poseidon and save his people. As Andromeda lay chained to the rocks, Perseus flew past and was struck by her beauty. He offered to slay Cetus to save Andromeda if Cepheus would give him her hand in marriage and a kingdom. The king immediately agreed. One version of the story has Perseus using Medusa's head, which he'd recently cut off, to turn Cetus to stone, or perhaps he used his sword. In any case, the sea monster was vanquished and Andromeda freed. After similarly dispatching Andromeda's former suitor, Agenor, and his army, Perseus and Andromeda were wed. For keeping her parents' promise, Andromeda was rewarded upon her death by being placed in the heavens by the goddess Athena. One of the stars in the constellation Andromeda, Upsilon Andromedae, was the first star similar to our Sun that has been identified as having planets circling it, with three found to date. This suggests that most stars may have planets, greatly increasing the likelihood of life elsewhere in the universe. But the most amazing object in Andromeda is the Great Spiral Galaxy, M31. At only 2.4 million light-years away, it is visible to the naked eye from a dark-sky location. See our sky map for its location in Andromeda. While you can make out the smudge that is M31 with the naked eye, larger optical aids will give you a more detailed view. A telescope will also bring in two of its 11 companion galaxies, M32 and M110. A very large telescope brings the spiral structure into focus. A telescope more than 10 inches in diameter allows you to find a few of the brightest of Andromeda's own swarm of globular clusters. M31 is a spiral-type galaxy, just like our own Milky Way galaxy. Astronomers can study features in Andromeda similar to features in the Milky Way that are obscured by the dust and gas in our galaxy. The spiral structure was only seen when M31 was first photographed in 1887. Like the Milky Way, M31 has a black hole at its heart that weighs in at 30 million times the mass of our Sun. M31 actually has two nuclei, indicating that M31 has absorbed at least one other galaxy in the past. Being so relatively close, M31 has figured prominently in the history of astronomy, including the determination of the distance scale of the universe and the evolution of galaxies. When you look at M31, you will be looking 2.4 million years into history at the same time you are looking at a famous object in the history of astronomy.
The Planets for January 2005 When it gets dark in January, you will be able to find the Ringed Planet, Saturn, rising in the east-northeast. Saturn is still located in the eastern part of Gemini, where it will remain all month. Pollux and Castor, the two bright stars at the heads of Gemini, the Twins, are well north of Saturn. Saturn reaches opposition on Jan. 13, meaning that the Sun and the planet are 180 degrees apart along the ecliptic. This is usually where the planet is the brightest, and Saturn is no exception, reaching its brightest magnitude for the entire year at magnitude -0.75 at mid-month. Through the telescope, Saturn's ball is 20.5 seconds of arc across. The rings are becoming increasingly open at 22.5 degrees, with the southern face showing, and they are 46.5 seconds of arc across. The constellation Virgo is home for Jupiter this month. Jupiter will be in the sky only during the mornings, having risen at midnight. It is slowly brightening, being magnitude -2.1 at mid-month. Jupiter's equatorial diameter this month is 37.5 seconds of arc. When viewing the planet through a telescope, the four "stars" that line up on either side of the planet are the Galilean moons--Io, Ganymede, Europa and Callisto. On Jan. 31, at 2 a.m., Jupiter will be 1.1 degrees north of the Moon, making a nice pairing in our morning sky. Mars is next up in our sky, rising around 4:30 a.m. It moves from Scorpius to Ophiuchus early in the month. Shining at magnitude +1.5, the Red Planet is a tiny 4.5 seconds of arc across, making it very difficult to see any features through a telescope. Venus pops up shortly before the Sun. It starts the month in Ophiuchus and slides quickly into Sagittarius. It will be accompanied all month by Mercury, which will be west of Venus at the beginning of the month, but passes Venus on Jan. 14 as it heads east faster. The planets will be only 0.3 degrees apart at their closest approach. The pair will be swallowed up in the bright morning twilight toward the end of the month. At mid-month, Venus is magnitude -3.9 and 10.5 seconds of arc across. Mercury is much dimmer at magnitude -0.3, and is half Venus' size. Enjoy this morning pairing and "keep watching the sky"!
|
