AMATEUR ASTRONOMY:

GEMINID METEOR SHOWER TONIGHT AND TOMORROW NIGHT:

The Geminid meteor shower, which usually peaks each year between December 12th and December 14th, is the most reliable and spectacular of the annual meteor showers even though observation is less comfortable than that of other showers such as the summer Perseids. On the other hand the skies are usually clearer in winter than at other times of the year. This year the predicted peak will occur at 16:45 GMT on December 14th. This is 10:45 here in Winnipeg in the CST zone. Consult the Time and Date.Com website for the equivalent time in your locality. Time and Date also gives the times of Sunrise/sunset and Moonrise/Moonset as well as a weather forecast. This year the Moon will not interfere with viewing as it is a thin waxing crescent that sets at 8:18 pm. The expected peak time will unfortunately occur during daylight, but a large number of meteors are likely to be visible tonight, especially in the early morning hours, or tomorrow night. The Geminids have a rather extended peak so that viewing doesn't depend on getting an exact time. All weather reports, whether from Time and Date, from Environment Canada or from the Clear Dark Sky website, indicate good clear viewing conditions tonight but overcast tomorrow night. The Clear Dark Sky site has a wealth of other useful information as to viewing conditions for a vast number of locations in North America.

The Geminids are a rather recent meteor shower, having first been observed by astronomers R.P. Greg, B.V Marsh and A.C. Twining first observed them. They were observed again in 1863 by A.A. Herschel. It was only during the 1870s that astronomers realized that a new annual shower was underway. The Geminids gradually increased in intensity during the last century. This year there may be as many as 120 meteors visible per hour near the peak period. Intensity will decrease only slightly from 6 to 1o hours on either side of the peak. The intensity increases gradually in the 2 to 3 days prior to the peak and then falls off rapidly. Thus tonight should be a good time for viewing, specially after 2:00 am when Gemini is high in the sky (the number of meteors visible is largest when their radiant approaches the zenith).

The meteors of the Geminids are of medium speed, approaching Earth at about 35 kilometers per second. They are bright and usually white in colour, and are often productive of some spectacular fireballs. Their apparent speed is slow, and they can sometimes been seen to have jagged paths and to seemingly split. They leave few visible trails however. The radiant will come from a point just to the northwest of Castor, the upper star in the constellation (see diagram above). The Geminids are rather unique in that they originate from an earth-crossing asteroid, 3200 Phaeton, unlike other meteor showers which originate from cometary debris. This parent body was discovered as recently as 1983 by S. Green and J.K. Davies, using the Infrared Astronomical Satellite. This year Phaeton will be making its closest approach since 1983, coming within 11 million miles of Earth. There is some dispute about the nature of Phaeton as some believe that it is not an asteroid but rather the burnt-out nucleus of a comet.

So look to the northeast early this evening, and higher in the sky later to find Gemini, and happy frigid viewing. Have a look out for Mars as well. It shines brightly at the right-hand side of Gemini as it merges into Taurus. But more on Gemini and Mars later.

OCCULTATION OF SATURN AND THE STARS OF GEMINI:

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.

SATURN SPOTTING:

The planet Saturn is presently making one of its retrograde motions and passing from the constellation of Leo westward to the faint constellation of Cancer. It previously passed to Leo from cancer last fall in Sept and Oct.. Looking down the alley from her city location Molly cannot distinguish any of the stars of Cancer, but she can easily make out most of the stars of Leo and at least Castor, Pollux, Tejat and Alhena in Gemini (the constellation immediately to the west of Cancer). Saturn is about 15 degrees to the west of Algiebra(the second star in the "hook" of Leo, and a bit further towards the zenith than the bright star Regulus (the beginning of the "hook"). Viewing is a bit restricted because of the light of the first quarter Moon. Tonight, at about 11:00 pm Central Standard Time, Leo and Saturn are a bit to the east of due south. Orion has begun to advance towards the horizon in the southwest. Sirius, the brightest star in the sky, is almost due south.

For further information on the planet Saturn go to the Wikipedia article and the Nine Planets site. The two sites complement each other.

A little interesting Saturn factoid. The actual length of a Saturnian day is uncertain. The gaseous nature of the planet leaves no firm "handle" to measure the period of rotation. Astronomers have relied on radio measurements of the planet's magnetic field to make their estimates, but recent findings have shown that geyser activity on the small Saturnian moon Encaledus inhibits the rotation of the planet's magnetic field to a speed less than that of the actual rotation. The most recent measurements place Saturn's "day" as about 10 hours and 47 minutes. Interestingly enough comparative measurements have shown that this is about 6 to 8 minutes longer than the time Saturn took to rotate in the 1980s when the first measurements were taken.

Anyways, more on Saturn, Leo and the other constellations mentioned later.

Molly