The science of meteor astronomy began in November 1833 when observers throughout America were treated to a spectacular meteor display.

• “[There were] thousands of luminous bodies shooting across the firmament in every direction. There was little wind and not a trace of clouds, and the meteors succeeded each other in quick succession.”
• “At Boston, the frequency of meteors was estimated to be about half that of flakes of snow in an average snowstorm”
• There was a belief that the stars were falling from the skies. Impromptu prayer meetings were held.
• At Independence, Missouri, local Indians used the signal to push the Mormon community out of town onto the Oregon trail.
• In 1878 the historian R. M. Devens listed the meteor storm as one of the 100 most memorable events in U.S. history.

These enigmatic lines of light falling through the night sky have puzzled stargazers for millennia. Like comets with their fireballs, these strands of light have satisfied soothsayers and portents of doom for millennia. 

Woodcut print depicts the shower as seen at Niagara Falls, New York. Mechanics’ Magazine said this illustration was made by an editor named Pickering “who witnessed the scene.” Source: Wikipedia

Twenty six years earlier, in 1807 Professor Benjamin Silliman made the outrageous  suggestion that meteors came from outer space. His views were quickly dismissed by none other than Benjamim Franklin.

Now there was no doubt.  Keen observers  saw  that the meteors come from the Constellation of Leo. Academics coined the phrase the Leonids and Professor Denison Olmsted confirmed that they came from space. This was the greatest meteor display in recorded history.

There was another spectacular, but less grand display in 1865/6. During that winter Ernst Temple and Horace Temple Tuttle independently discovered a comet that we now call Comet Temple-Tuttle. Giovanni Schiaparelli, the man now known for his belief that there were canals on Mars, realised that the orbit of the Leonid shower coincided with that the comet.  Schiaparelli deduced that the spectacular display was due to dust from the comet.  He reasoned that the comet ought to reappear every thirty three years.

Puzzlingly, the displays of 1896 and 1933 were a disappointment. The astronomer, Dorethea Klumke, was so keen to see the display that she commissioned a hot air balloon. On 16th November 1896, in the first example of airborne astronomy, she ascended from a Paris field. She saw saw 30 meteors, but only 15 Leonids, in 5 hour period. The trajectory of the comet was lost.

In 1966 the northern hemisphere was treated to a spectacular display; meteors streaked down at an alarming rate.  Astronomers refound the comet.  Spectacular displays followed in 1998 to 2002.

Why were the Leonid displays so unpredictable?

Astronomers thought that they understood the basics.  When comets approach the sun part of their surface evaporates producing a tail.  In 1950 Fred Lawrence Whipple explained this by the dirty snowball hypothesis. He thought comets were made of rock and dust  bound into an iceball. When the ice melts, the dust forms the tail of the comet. . Every thirty three years Comet Temple Tuttle makes its closest approach to the sun and produces a new dust tail.  When the Earth passes through the tail of a comet the dust burns up in the atmosphere. In the meteor shows we see those glowing particles of dust. The Leonid display is impressive not just because of the number of particles involved, Comet Temple Tuttle orbits the sun in a reverse direction to the Earth.  The dust particles make head on collisions at 70hm/hr, twice as fast as other meteor impacts.

The puzzle lies in predicting the trajectory of the dust cloud. Every 33 years a new dust plume is produced. The closer the comet approaches to the sun, the more dust is released and the stronger the plume should be. In 1833 the Earth made a very close approach to Comet Temple Huttle.  The Earth does not usually pass through the tail of the latest plume. It usually passes through older lower density plumes.  In 1833 the Earth made a direct hit with 1800 dust. In 1966 the Earth went through 1896 dust.  In 2001 and 2002 the comet went through dust dating from 1767 and 1833 respectively.

A good meteor display will require the Earth to pass through a rent dust cloud caused by a close approach of the comet to the sun. Although scientists have developed models to predict the position of the dust clouds, these need to be extremely accurate to predict which cloud will interact with the Earth.

Sometimes the Earth passes through dust that has been left behind by the comet.  This means that a good display is possible on years between the 33 year intervals.

Scientists say that the Leonid display on 17th November 2009 will be spectacular. 

Perhaps this is best seen in perspective. In 1833 some 70,000 meteors were seen per hour, which would have seemed like a blizzard.  In 2009 some 500 meteors are expected per hour, which is still spectacular. In most years just 15 Leonids are seen per hour on a November night.

This may be our last chance to see the meteor display for some time.  A close encounter with Jupiter is expected to change the orbit of the comet and dust cloud and swing them away from the Earth.