Observer's Notebook for November 1999
by John Rummel
Will the Lion Bare his Teeth?
The meteors of November, the Leonids, are the most famous of showers, perhaps because they were the first to be recognized as an astronomical event, and not some freak atmospheric phenomenon.
The night of November 12-13, 1833 started out normally enough. Lanterns were dimmed, fires went out, the children were put to bed. Before long, however, even the soundest sleepers had been roused by the shouts from the street. After midnight, the sky had come alive with shooting stars and fireballs. Virtually everyone has seen a shooting star, that fleeting streak that is gone almost before you've had a chance to focus on it. This was different though. Meteors were coming about one every second. Then several every second. By the time the night was over, objective observers up and down the east coast of the United States estimated counts as high as thousands per minute. It must have seemed as if the entire sky was falling. Many people were simply terrified.
Newspapers in the days following left little doubt that this night had touched almost everyone. The true nature of meteors was not then known - many speculated that some strange gas in the atmosphere had been ignited by electrical charges. Others, not so scientifically oriented, suggested that Judgment Day was at hand.
Photo by Michael McDowell. Cepheus region with Leonid.
Astronomers noted that the event was localized. Most cities in the eastern United States reported the shower. It was not reported west of the Mississippi, nor was it seen in Europe. Some recalled that there had been a similar, though not as spectacular, storm back in November of 1799, visible from South America.
Astronomers also noted that the shooting stars all seemed to radiate from a particular point in the sky, centered around the constellation Leo, high in the southern sky late that November night. One astronomer in particular, Denison Olmstead of Yale University, hatched a theory that the shooting stars came from a cloud floating in space. He noted that the November shower returned in 1834, though not nearly as stunning as they had been the previous year. Olmstead suggested that the Earth passed through this cloud every November as it orbited the sun. Each November finds Earth "hurtling toward" Leo as it orbits the sun. Thus, to Earthbound observers, it looks as though the meteors come from that direction. From that moment, the November meteors were known as the "Leonids," and the phenomenon of meteor showers got a lot more attention from astronomers.
As the years went by, other historians and scientists found many more examples of brilliant November meteor displays, some going back as far as 2000 years. By 1837, astronomers had analyzed all the data, and concluded that though the shower happens every November, every 33 or 34 years, it is particularly brilliant.
Sure enough, 1866 and 1867 produced significant showers, upwards of 2 to 5 thousand per hour, though 1867 was spoiled by a nearly full moon.
The year 1867 marked a turning point in our understanding of meteors. Two years earlier, in December 1865, a French astronomer, Ernst Wilhelm Liebrecht Tempel, had discovered a faint and fairly undistinguished comet, now known as Comet Tempel-Tuttle (so-known because it was independently discovered by Horace Parnell Tuttle a few weeks later). The faint comet quickly faded from view, but astronomers were able to calculate an orbital period of about 33 years.
In 1867, Italian astronomer J. V. Schiaparelli wrote an article in which he speculated that the comet was probably related to the 1833 and 1866 meteor showers. This conclusion was reached by several others as well, and it soon became clear that Tempel-Tuttle was somehow spewing debris in its wake, and that this debris continued to orbit the sun in Tempel-Tuttle's path, which is intersected by the Earth's orbit each year in November. When the Earth passes through the debris field, a meteor shower results. The showers are more intense in the years immediately following Tempel-Tuttle's close passage through the inner solar system.
Subsequent Leonid peaks since the 1833 and 1866 storms have been mixed. Some were probably muted because peak rates happened over unpopulated areas, some were spoiled because of the bright full moon. The shower of 1966 produced rates of 100,000 shooting stars per hour in the southwestern United States, but viewers in most locations reported something around 200 per hour.
Comet Tempel-Tuttle passed through the inner solar system - and by the Earth - in February 1998. For this reason, most experts predicted that 1998 and 1999 would bring repeat performances of earlier wondrous Leonid peaks. While the 1998 Leonid storm was rewarding to those who ventured out to dark sky country to watch, the United States was not well placed when Earth passed through the main stream. Observers in Japan and eastern Asia had the best view. Unfortunately for this year, the U.S. will again be in daylight when the peak arrives. In 1999, you'll have to head to Europe or northern Africa for a chance to see the peak storm.
However, observers in Madison and surrounding areas can still observe a wonderful Leonid show. Off-peak years may produce displays of about 25 to 40 meteors per hour. Peak years like this, even if you're on the wrong part of the planet, almost always produce rewarding displays. The peak this year is predicted to be November 17th, but any night a few days to either side of this should see meteor counts as high as 50-60 per minute. Find a dark site, away from city lights. The best time to observe is between midnight and dawn. Since the 17th is a Wednesday - and a school day - you may find it more practical to get the kids up an hour before dawn. For best results, don't stare right at the constellation Leo. Meteors will appear in all parts of the sky, but their paths will usually trace back in the direction of Leo. Make sure you dress warmly; November mornings are sure to be quite chilly. Take a thermos of hot chocolate or coffee. Most importantly, go with a friend or two. Sharing the show makes it even more enjoyable, and two pairs of eyes will see twice as many Leonids.
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