Tuesday, April 24, 2007

The Moon, now in its first quarter has moved out of the constellation Gemini and is now entering Leo via the very dim constellation of Cancer (hardly visible at all except in the clearest skies) When you look up tonight you can see the Moon separated by only about 2 or 3 degrees from Saturn which now lie just to the west of Regulus, the star that marks the beginning of the "hook" in Leo. Saturn is actually quite good for viewing at this time as its rings have a 15 degree tilt, and are quite visible. Tomorrow (april 25th), however, may be even better as the Moon and Saturn will reach their closest approach. In Northern Canada, Alaska, the west coast of Canada and the upper north west of the USA there will actually be an occultation of Saturn by the Moon. The occultation will occur at about 10:28 UT in Vancouver and at about 10:30 UT in Victoria BC. This translates to a local time of about 2:40 am in Victoria. In Edmonton Alberta it will begin slightly earlier, at 10:17 UT. Go to the Lunar Occulatations site for further information.
As long as the Moon is leaving Gemini it's perhaps time to visit the stars of this constellation. Refer to the above diagram for what follows, and imagine it as being rotated 90 degrees counterclockwise so that Castor is higher in the sky than its brighter companion Pollux. The above diagram, however, better illustrates how this constellation resembles two stick men side by side, the "twins". The apparent orientation of Gemini changes throughout the year. Presently it is gradually returning from a "left" rotation, and it will gradually become more horizontal until it is no longer visible come the month of June. When it returns in the late fall it will considerably rotated "clockwise". At that time one of the stars is within the Milky Way and one is outside of it. This is connected with the legend of "cattle theft" associated with this constellation (see later).
The twins are called the Dioskouroi in Greek mythology, meaning "youths of Zeus (the god), and Pollux is often referred to as 'Polydeuces'. The Greek legends probably derive from more ancient Indo-European myths as the twin horsemen, the Asvins, occur in the Vedas and the Alcis twins figure in Germanic mythology. In Rome they were sometimes confused with Romulus and Remus. In China, on the other hand, these stars are associated with the yin and yang of nature. The twins in such legends are usually depicted as unequal. Another Greek example of such a configuration is the Ampion/Zethus pair from Thebes. Various versions of the Greek legends exist. Sometimes both twins are immortal, sometimes neither and sometimes only one. If only one it is Pollux/Polydeuces who is the immortal one. The most common legend is that Zeus, disguised as a swan, seduced their mother Leda, and that the two brothers were born from eggs. The representations of the Dioscuri in vase painting feature skullcaps that are said to be remanants of the eggs.
In some versions Tyndareus, King of Sparta, is merely their step father. In others he is the father of Castor but not of Polydeucis. Their sisters were Helen of Troy and Clytemnestra. They were reportedly brought up by the centaur Chiron(represented by the constellation Centaurs), and later they joined Jason, who was also reportedly brought up by Chiron, in the quest for the Golden Fleece. They also were said to have rescued their sister Helen when she was carried off by Theseus and Pirithous. Seems like Helen tried more than once to get out of Sparta. The twins had a general connection to Sparta, and their duality was reflected in the two kings of Spartan government. Their grave shrine was at Therapne, across the Eurotas River from Sparta.
The Dioscuri met their match in the twin brothers of Thebes, Idas and Lynceus, when Castor and Polydeuces abducted the daughters of Leucippus, Phoebe and Hilaeira, known as the Leucippides ("white horses"). Seems the Greeks did a lot of kidnapping. Castor was supposedly killed in this encounter, and his brother pleaded with Zeus to grant him half his immortality. From that time forward each twin spent alternating days on Olympus and in Hades. Thus they weren't present at the siege of Troy. When the constellation is rotated clockwise it appears as if one of the twins is "stealing the cattle" from the Milky Way while the other looks on. Castor and Polydeucis are considered the patrons of mariners because of their role in calming a storm during the voyage of the Argo.
The two brightest stars of Gemini are Castor (now higher than Pollux) and Pollux. Pollux is the brightest at a magnitude of 1.1. It is an orange star that lies at a distance of 36 light years (lys). Castor is the second brightest at magnitude 1.6. It is a blue white star at a distance of 46 lys. It is actually a septuplet, and the individual stars have far lesser magnitudes than the combined brightness of the naked eye object. Mebutsa (on the upper arm of Gemini, going west comes from the Arabic for "lion's paw", but the name is only recent. it is a yellow white star of magnitude 3.0 and lies 685 lys away. Going further to the west we come to Tejat, and orange red star of magnitude 2.9 that lies 150 light years away. On the lower arm of Gemini we find Wasat, meaning "the middle" in Arabic, another recent name. It is a whitish double star of magnitude 3.5 (the brighter of the pair) and is 58 light years away. The now demoted "planet" Pluto was found close to this star in 1930. Further to the west is Mekbuda, which also means "lion's paw". It is a yellow white variable star with magnitude 3.7 to 4.2 every 10 days. It is 1,400 lys away. Then at the furthest west we come to Alhena meaning "mark on the neck of a camel". It is a blue white star of magnitude 1.9 and is about 85 lys away. One named star not shown in the above diagram is Propus, the "forward foot" of Castor. It is a little to the west of Tejat. It is an orange red variable star (magnitude 3 to 4 over 233 days), and is about 185 light years away.
The reader should note that the magnitudes listed above are "inverse". The smaller the number the greater the apparent brightness. In a city sky pretty well all that can be seen of Gemini is Castor and Pollux. On an exceptionally clear night some of the other stars named above can be visualized.

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