The History of the Leonid Storms

Leonid meteors have been observed for over a thousand years, and sometimes this shower does produce storms. Arab astronomers mention a prominent display in 902 A.D., and the German naturalist Baron von Humboldt wrote in 1799 that meteors from the constellation Leo fell “like snowflakes” from the sky.

On November 17, 1833, however, something extraordinary occurred. Before dawn that morning, the sky over eastern North America became the tableau for one of the most spectacular meteor storms ever recorded. Within a few hours, over 200,000 were seen from a single location. At one point, there were so many meteors visible that witnesses could easily trace their paths backward on the sky to a fixed point in the neck of Leo the Lion. This point in the sky from which the meteors appeared to emanate was later referred to as the shower’s radiant.

After this staggering display, astronomical historians reviewed the records of earlier Leonid performances in an effort to track down previous storms. They discovered that between the years A.D. 902 and 1833, a period of 931 years, there were 28 notable meteor showers around the time of the Leonids, though none with the intensity of the 1833 display. They also found evidence of increased activity in the one to two years prior to the main outburst. This indicated that the shower peaked as a major storm every 33.25 years. If so, then the particles in the Leonid stream were not uniformly distributed throughout its orbit but bunched together in aggregates of material of varied density.

Armed with this evidence, Hubert Anson Newton, who was chairman of the mathematics department at Yale College, predicted that another Leonid storm would occur in November 1866. His prediction was confirmed when the meteors appeared on schedule the morning of the 17th of that year. Although the display wasn’t as extreme as it had been in 1833, their reappearance established the 33-year cycle. It also further substantiated the idea that meteors and comets were somehow related, an idea that was first suspected by some scientists at the beginning of the nineteenth century.

Further proof of this relationship arose from the work of the Italian astronomer Giovanni Virginio Schiaparelli, who, in 1866, noted that meteors appeared more frequently in the predawn hours than in the evening. The reason: during the hours between midnight and dawn, the still-darkened morning side of the Earth faces directly into its orbit, thus easily sweeping up any interplanetary dust it encounters. On the other hand, for these same dust particles to be seen before midnight, they must travel fast enough to catch up with Earth’s trailing evening side.

Schiaparelli found that the velocities of these meteors nearly matched those of comets moving in parabolic orbits — and events moved swiftly thereafter. Astronomers realized that a comet observed that same year, Comet Temple-Tuttle (designated 1866 I), followed an orbit that was identical with that of the Leonid meteor stream. This discovery firmly established the comet-meteor shower link by showing that a meteor shower occurs when Earth passes through a trail of cometary debris.

By the late nineteenth century, the nature of meteor streams was more firmly understood, and nearly all meteor showers were soon identified with a parent comet. Given the reliable appearance of previous Leonid meteor storms, the general public greatly anticipated another storm in 1899. But they were to be sorely disappointed. No significant shower occurred that year. Apparently, Jupiter’s gravity had perturbed the Leonid stream slightly out of Earth’s central orbital path.

In 1925, meteor observer Charles Oliver wrote, “The failure of the Leonids to return in 1899 was the worst blow ever suffered by astronomy in the eyes of the public.” Ironically, this wouldn’t be the last time an expected astronomical event would fail public expectations. People were further let down 33 years later in 1932 when a Leonid storm again failed to materialize. After this second no-show, some scientists thought the previous planetary perturbations would prevent the storm phenomenon from ever being seen again. But by the 1950s, meteor observers were reporting a steady increase in activity, and some astronomers predicted that a storm might occur the morning of November 17, 1966. Those predictions turned out to be correct.

The 1966 Storm

Anyone who saw the 1966 Leonid storm will not soon forget it. On the morning of November 17, observers across the central United States saw an estimated 150,000 meteors per hour. The Leonids had clearly reestablished itself as the mother of all meteor storms.

That year, I, like everyone else, had heard of an impending “storm” of meteors. I was living in Corpus Christi, Texas, at the time, however, and November is not a good time of the year for skywatching in south Texas. Nevertheless, I went out around 3 a.m. looking for meteors. Jupiter was well up in the east, preceding Leo, which was just coming up over a tall stand of cottonwood trees across the street. The sky was patchy with low clouds, but it was clear enough to see that there were no meteors. At four, I went out again, and an all-too familiar sight greeted my eyes: a ceiling of low cumulus clouds passing overhead from the southeast. For a long while I stood there hoping for a break in the clouds. I could see that they were thinner in some places, and it is not unusual in south Texas for a stratum of clouds to roll out creating a brief clearing of sky before another stratum rolls in. In the vernacular of amateur astronomy, these are called “sucker holes.”

I waited fifteen or twenty minutes before I noticed a large break in the clouds coming my way. As it approached, I recognized Regulus and the familiar sickle asterism forming the Lion’s head, which was by now high in the east. It was at that moment I saw a meteor flit through the space in the clouds. When the cloud opening was practically overhead, I saw another. My frustration mounted as another round of clouds closed in. I awaited each “hole” no matter how small to catch a fleeting glimpse of the meteors. Eventually a large ragged edged window presented itself, and through that momentary portal, I saw meteor after meteor, flashing by like frenetic fireflies.

Larger cloud openings showed a sky full of meteors, enough to make me feel that I were staring down into a cone from which the meteors emerged. At the center of this cone was the radiant point, the region of sky out of which the meteors appeared. A couple of years later, I would recall a similar feeling watching the “light show” sequence in the movie, 2001: A Space Odyssey. Since that night, I’ve looked forward to the next Leonid storm.

What you have in your mind?