Leonids

A famous depiction of the 1833 meteor storm, produced in 1889 for the Adventist book Bible Readings for the Home Circle.

For other uses, see Leonid.

The Leonids ([ˈli.əˌnɪdz] lee-uh-nids) are a prolific meteor shower associated with the comet Tempel-Tuttle. The Leonids get their name from the location of their radiant in the constellation Leo: the meteors appear to radiate from that point in the sky. The 2009 display peaking on November 17 may produce more than 500 meteors an hour.

Earth moves through the meteoroid stream of particles left from the passages of a comet. The stream comprises solid particles, known as meteoroids, ejected by the comet as its frozen gases evaporate under the heat of the Sun when it is close enough - typically closer than Jupiter's orbit. The Leonids are a fast moving stream which come close to or cross the path of the Earth and impact the Earth at 72 km/s. Leonids in particular are well known for having bright meteors or fireballs which may be 9mm across and have 85g of mass and punch into the atmosphere like a car hitting at 60mph. An annual Leonid shower may deposit 12 or 13 tons of particles across the entire planet. Sometimes these trails of meteoroids cause meteor showers and sometimes meteor storms.

The meteoroids left by the comet are organized in trails in orbits similar to though different from that of the comet. They are differentially disturbed by the planets, in particular Jupiter and sunlight/solar wind (see also a full explanation by McNaught & Asher (1999)). Old trails are spatially not dense and compose the meteor shower with a few meteors per minute. In the case of the Leonids that tends to peak around November 17, but some are spread through several days on either side and the specific peak changing every year. Conversely, young trails are spatially very dense and the cause of meteor storms when the Earth enters one. Usual counts during a storm exceed 1000 meteors per hour, to be compared to the annual background (1 to 2 meteors per hour) and the shower background (a few per hour).

History

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."

The Leonids are famous because their meteor showers, or storms, can be, and have been in a few cases, among the most spectacular. Because of the superlative storm of 1833 and the recent developments in scientific thought the Leonids have had a major effect on the development of the scientific study of meteors which had previously been thought to be atmospheric phenomena. The meteor storm of 1833 was of truly superlative strength. One estimate is over one hundred thousand meteors an hour, but another, done as the storm abated, estimated in excess of two hundred thousand meteors an hour over the entire region of North America east of the Rocky Mountains. It was marked by the Native Americans, slaves and owners, and many others. That same 1833 shower, near Independence, Missouri, was taken as a sign to push the growing Mormon community out of the area.

Accounts of the 1866 repeat of the Leonids counted hundreds per minute/a few thousand per hr in Europe. Later work identified the meteoroids from the 1733 passage of Comet Temple-Tuttle. The Leonids were again seen in 1867, when moonlight reduced the rates to 1000 per hour. Another strong appearance of the Leonids in 1868 reached an intensity of 1000 per hour in dark skies. It was in 1866-7 that information on Comet Temple-Tuttle was gathered pointing it out as the source of the meteor shower. When the storms failed to return in 1899, it was generally thought that the dust had moved on and storms were a thing of the past. Then, in 1966 a spectacular storm was seen over the Americas. Leading up to the 1998 return, an airborne observing campaign was organized to mobilize modern observing techniques by Peter Jenniskens at NASA Ames Research Center. This resulted in spectacular footage from the 1999, 2001 and 2002 storms producing up to 3,000 Leonid meteors per hour. Initially, the exact location of the dust was unknown. A graph published in Sky and Telescope adapted from Comet 55P/Tempel-Tuttle and the Leonid Meteors(1996, see p. 6) shows relative positions of the Earth and Tempel-Tuttle and marks where Earth encountered dense dust. This showed that the particles are behind and outside the path of the comet, but paths resulting in powerful storms were very near paths of nearly no activity. The work of David Asher, Armagh Observatory and Robert H. McNaught, Siding Spring Observatory, and independently of Esko Lyytinen in Finland, following on from the pioneering research by Kondrat'eva, Reznikov and colleagues at Kazan, is considered by most meteor experts as the breakthrough in modern analysis of meteor storms. Whereas previously it was hazardous to guess if there would be a storm or little activity, the predictions of Asher and McNaught timed bursts in activity down to five minutes. However, the relative brightness of the meteors is still not understood. The double spikes in Leonid activity in 2001 and in 2002 were due to the passage of the comet's dust ejected in 1767 and 1866. The 1833 storm was not due to the recent passage of the comet, but from a direct hit with the 1800 dust and the 1966 storm was from the 1899 passage of the comet. Examples of other streams accounting for spikes in activity include the 2004 June Bootids. Peter Jenniskens has published predictions for the next 50 years.

However, a close encounter with Jupiter is expected to perturb the comet's path, and many streams, making storms of historic magnitude unlikely for many decades.

Year	Leonids active between	Peak of shower
2008	November 14 - 22	Nov. 17, 2008
2009	November 10-21	Nov. 17, 2009 ZHRmax ranging from 300 to 400 predicted per hour

• "There are no guarantees in meteor work ... observers should be alert as often as conditions allow throughout the shower, in case something unexpected happens, this year 2009 the best viewing spots will be Southern Asia, Northern and Eastern Australia."

See also

• Meteor showers
• List of meteor showers
• Stars Fell on Alabama, based on the 1833 Leonid shower

External links

• Leonid History by Gary W. Kronk
• Leonid dust trails by David Asher
• The Great Leonid Meteor Storm of 1833. A first-hand account by Elder Samuel Rogers
• The Discovery of the Perseid Meteors (after the Leonids and) Prior to 1837, nobody realized the Perseids were an annual event, by Mark Littmann
• The Night the Stars Fell My Search for Amanda Young a slave narrative.
• Winter Counts The Native Voice By Lise Balk King
• Lunar Leonids: Encounters of the Moon with Leonid dust trails by Robert H. McNaught
• Brilliant Leonid storm likely fodder for later Lincoln speech by Jim Vertuno
• NASA: Background facts on meteors and meteor showers
• NASA: Estimate the best viewing times for your part of the world
• Science@NASA: Leonids 2006
• How to hear the Leonid Meteor Shower
• Observatorio ARVAL - The Leonid Meteors
• Animation of the Leonid Meteor Shower at shadow&substance.com
• Leonids at The Big Blog Theory