Astronomy news for the week starting Friday, November 13, 1998.

We begin the week with the crescent Moon waning toward full, making a lovely sight to the east before dawn. Our companion passes through its new phase around midnight the night of Wednesday the 18th, and by next Friday night will be visible as a thin crescent in western evening twilight. Giant Jupiter gets into the act this week too, in fact today, Friday the 13th, as it stops its retrograde westerly motion among the stars and begins once again to move in its normal easterly direction. Retrograde is only an apparent motion caused by the Earth passing between the planet and the Sun, and the Earth has moved far enough along in its path for us to see Jupiter's real motion. Now in eastern Aquarius, the planet will head toward the next constellation of the zodiac, Pisces.

The week belongs not to Jupiter or the Moon, however, but to the famed Leonid meteor shower, rather meteor storm, which occurs only once every 33 or so years on or about November 17 when the Earth passes through, or close to, a concentration of debris flaked off Comet 55P/Temple-Tuttle (the "P" standing for "periodic"). The comet has a 33 year period around the Sun, the stuff that causes the storm following in a thin ribbon behind it. Since the comet returned to our vicinity last January, we have a chance to see the storm once again. As the Earth plows through the cloud, the particles -- "meteoroids" -- hit the atmosphere at 70 kilometers per second, and nearly 100 kilometers up heat to some 6000 degrees centigrade, leaving a streak of electrified air behind them, the meteor easily visible on the ground. The particles are small, ranging from under a millimeter for those that produce the faintest meteors, to rather large pieces maybe up to a meter across that produce beautiful fireballs. All the debris is so fragile, though, that none ever hits the ground.

The stream of meteoroids is moving such that they seem to come out of the direction of the constellation Leo, and hence are called the "Leonid" shower. They can be spectacular. Meteor fall rates in 1833 are estimated at 100,000 per hour, the storm in 1799 not far behind. The 1866-1867 events (seen both years) were modest, while less was seen in 1900 and 1901, and nothing in 1933. But in 1967 it returned in wild proportions, with a rate for an hour or so close to that of 1833.

No one knows what will be seen. The best predictions are that we will hit the stream around 2 PM the afternoon of Tuesday the 17th in daylight in North America, making the meteors impossible to see here. However, there is so much uncertainty about the structure of the stream, that we may well see something the morning of Tuesday the 17th or Wednesday the 18th. The best time for viewing is after Leo rises, between about 2 AM and dawn. We may see nothing, we may be delighted with a great sky show, or find something in between. The only way to know, of course, is to find a dark location away from artificial lighting and look.
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