A Brief History of Meteor Storms
About 5 a.m. on the morning of November 13, 1833, people throughout the eastern United States were awakened from their sleep by lights from outside their homes. The lights turned out to be the flashes of fireballs! Sounder sleepers were awakened by excited voices that rose and fell, like a chorus, as the brighter meteors streamed into and out of view. At every instant dozens of meteors could be seen, filling the witnesses with awe and fear. A few of the brightest fireballs were both bigger in appearance and brighter than a Full Moon. 43 years later, Richard Devens described the scene as “the most grand and brilliant celestial phenomenon ever beheld and recorded by man.”
On the scientific front, this event led directly to the first widespread recognition that rocks sometimes fell from the skies, because all observers could plainly see that all the meteors were emanating from a single place among the stars, a place in the constellation Leo that appeared to move with the stars as the Earth rotated. On the religious front, so many people thought this event was, or foreshadowed, the coming of the end of the world that it is said to have been the primary impetus for the revival of religious fundamentalism in the United States that soon followed.
A “meteor storm” is distinguished from a common meteor shower by its intensity. If viewed in a clear, dark, moonless sky, a good meteor shower can produce about one meteor per minute on average, or occasionally more. That corresponds to 60 meteors per hour. By definition, the threshold for declaring a shower a “meteor storm” is a rate that exceeds 1000 meteors per hour, an average of one every 3.6 seconds.
On November 14, 1866, another Leonid meteor storm was seen in Europe. This confirmed a 33-34 year periodicity of the phenomenon, suspected because of reports of a meteor storm over the western Atlantic Ocean in November of 1799. From this event we also learned that the meteors in these storms follow nearly the same orbit as Comet Temple-Tuttle, which has a period of 33.2 years.
Based on this history, worldwide anticipation was high and widespread in 1899 when astronomers predicted the next Leonid meteor storm. But this time, the storm failed to materialize anywhere, leading to the assessment that this “… was the worst blow ever suffered by astronomy to the eyes of the public, and has indirectly done immense harm to the spread of the science among our citizens.” – Charles Oliver.
Hope was still high in 1932 and 1933, when a Leonid storm again failed to materialize. So astronomers concluded that the meteor orbits had been perturbed by the planets and dispersed. As a consequence, little public mention was made of the possibilities before the November 17, 1966 encounter of the Earth with the orbit of the meteor swarm. But the Leonids, as if only publicity shy, put on one of their most spectacular shows ever. In New Mexico and the western United States, lucky pre-dawn observers reported more meteors than could be counted, with peak rates reaching something on the order of 40 meteors per second! Witnesses described the experience as bringing home to them how fast the Earth they were standing on is actually rushing through space.
That brings us to 1998-1999. Several meteor experts predicted a possible meteor storm in November, 1998, leading NASA to put several satellites into a protective configuration and to postpone manned spaceflights until after the potential danger to unprotected astronauts had passed. Not only was there no storm, but to further embarrass the astronomers, the peak of the annual Leonid meteor shower (at several hundred meteors per hour off the west coast of Africa) happened about 16 hours before it was predicted to happen over Mongolia.
Up to that time, no Leonid meteor storm had ever been successfully predicted. Even the astronomers who have been bold enough to assert that a possible storm might occur had never been successful at predicting which part of the Earth would be facing the shower when it occurred. Indeed, Leonid storms are visible only over a rather narrow band of longitude because they peak during daylight hours when the radiant point in Leo is overhead. So visibility requires being at a longitude where the sky is still dark enough and the radiant point is well above the horizon. One must therefore know the time of the peak to within an hour or two to have any certainty of knowing what part of the Earth will be favored. Moreover, bright moonlight can interfere with meteor visibility; so only years when the Moon is set or near New Moon are suitable for viewing most storms in all their splendor.
For more information about the history of Leonid meteor storms, see the excellent book “The Heavens on Fire” by Mark Littmann, published by Cambridge University Press (1998).