Everything about Leonids totally explained
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For a list of famous people named Leonid, please see Leonid (a disambiguation page).
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 stream from that point in the
sky.
Meteor shower
The meteor shower is visible every year around
November 17, plus or minus a week, when the
Earth moves through the meteoroid stream of
particles left from the passages of the
comet. The stream comprises solid particles, known as
meteoroids, ejected by the comet as its frozen gases
evaporate under the heat of the
Sun which begins to warm the comet as it comes within the orbit of
Jupiter. A typical particle is no bigger than fine
dust. The main source of light of a
meteor is caused by the air molecules ramming the meteoroid, which fragments and atomizes the dust
(External Link
), and the resulting spray of microscopic debris collides with individual atoms of the atmosphere which then cool by glowing (not by friction as commonly thought). Larger particles leave a stream of smaller particles and form a
bolide or
fireball, which can leave a glowing trail in the atmosphere. Leonids in particular are well known for having such bright meteors.
The passage of the comet leaves these meteoroid particles distributed in similar
orbits to the comet itself and the average peak of activity, when the Earth passes the middle of the loose clouds of particles, is
November 17. In most years the
rate at which meteors are likely to be seen isn't great - one meteor every two or more minutes. However, in addition to the
random distribution of particles some can be shepherded by gravitational and radiation influences and form some clumping of orbits of the meteoroids. These are not trains of particles - one lined up behind the other. These are places where the orbits of particles nearly meet though at other parts of their orbits they may be far apart. When such a place
intersects with the
passage of the Earth a
meteor storm results and counts can far exceed both
background levels of meteors (of about one per hour) and of even the strongest regular meteor shower (of about one per
minute.)
History
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
(External Link), but another, done as the storm abated, estimated in excess of two hundred thousand meteors an hour
(External Link) 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. It was, in a word, unignorable. Many thought it was the end of the world.
Other great Leonid storms were seen in 1866 and 1867. 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. 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 Comet and marks where Earth encountered dense dust. This showed basically 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 that by Esko Lyytinen of Finland, following on from research by Kondrat'eva, Reznikov and colleagues at
Kazan, is generally considered 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, although 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.
(External Link) The 1833 storm wasn't due to the recent passage of the comet, but from a direct hit with the 1800 dust
(External Link) and the 1966 storm was from the 1899 passage of the comet.
(External Link) 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.
Further Information
Get more info on 'Leonids'.
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