Leonids sparkled over Canada ] By BBC Science's Dr Chris Riley on board NASA's Leonid mission</ref> Peter Jenniskens has published predictions for future dust trail encounters, resulting in a "meteor storm" or "meteor outburst", for the next 50 years. 
Over longer periods of time, the dust trails can evolve in complicated ways. One effect is that the orbits of some repeating comets, and meteoroids leaving them, are in resonant orbits with Jupiter or one of the other large planets - so many revolutions of one will equal another number of revolutions of the other. So over time since Jupiter will have the same relative position intermittently and it will tend to pull meteoroids into keeping that relative position. This creates a shower component called a "filament".
A second effect is a close encounter with a planet. When the meteoroids pass by Earth, some are accelerated (making wider orbits), others are decelerated (making shorter orbits), resulting in gaps in the dust trail in the next return (like opening a curtain, with grains piling up at the beginning and end of the gap). Also, Jupiter's perturbation can change sections of the dust trail dramatically, especially for short period comets, when the grains approach the big planet at their furthest point along the orbit around the Sun, moving most slowly. As a result, the trail has a clumping, a braiding or a tangling of crescents, of each individual release of material.
The third effect is that of radiation pressure which will push less massive particles into orbits further from the sun - while more massive objects (responsible for bolides or fireballs) will tend to be affected less by radiation pressure. This makes some dust trail encounters rich in bright meteors, others rich in faint meteors. Over time, these effects disperse the meteoroids and create a broader stream. The meteors we see from these streams are part of annual showers, because Earth encounters those streams every year at much the same rate.
When the meteoroids collide with other meteoroids in the zodiacal cloud, they lose their stream association and become part of the "sporadic meteors" background. Long since dispersed from any stream or trail, they form isolated meteors, not a part of any shower. These random meteors will not appear to come from the radiant of the main shower.
The radiant point
Because meteor shower particles are all traveling in parallel paths, and at the same velocity, they will all appear to an observer below to radiate away from a single point among the constellations. This radiant point is caused by the effect of perspective, similar to railroad tracks converging at a single vanishing point on the horizon when viewed from the middle of the tracks. Meteor showers are}} almost always named after the constellation from which the meteors appear to originate. This "fixed point" slowly moves across the sky during the night due to the Earth turning on its axis, the same reason the stars appear to slowly march across the sky. The radiant also moves slightly from night to night against the background stars (radiant drift) due to the Earth moving in its orbit around the sun. See "IMO" Meteor Shower Calendar 2007(International Meteor Organization) for maps of drifting "fixed points".
Notable meteor showers Edit
Perseid and Leonid meteor showers Edit
The most visible meteor shower in most years are the Perseids, which peak on August 12th of each year at over 1 meteor a minute.
The most spectacular meteor shower is probably the Leonids, the King of Meteor Showers which peaks on a day near 17 November. Approximately every 33 years the Leonid shower produces a "meteor storm" with hundreds of thousands of meteors per hour. These Leonid storms gave birth to the term "meteor shower" since most meteor showers produce only a few meteors per hour, rarely producing as many as one meteor every 30 seconds. The last two massive Leonid storms were in 1933 and 1966. The anticipated storm of 1999 was much less spectacular. When the Leonid shower is not storming it is less active than the Perseids.
Other notable meteor showers Edit
- Further information: List of meteor showers
|Quadrantids||Early January||The same as the parent object of minor planet 2003 EH1, comets C/1490 Y1 and C/1385 U1 |
|Lyrids||late April||Comet Thatcher|
|Pi Puppids||late April||Comet 26P/Grigg-Skjellerup|
|Eta Aquarids||early May||Comet 1P/Halley|
|Arietids||mid June||Comet 96P/Machholz, Marsden and Kracht comet groups complex |
|June Bootids||late June||Comet 7P/Pons-Winnecke|
|Southern Delta Aquarids||late July||Comet 96P/Machholz, Marsden and Kracht comet groups complex |
|Draconids||early October||Comet 21P/Giacobini-Zinner|
|Orionids||late October||Comet 1P/Halley|
|Southern Taurids||early November||Comet 2P/Encke|
|Northern Taurids||mid-November|| Minor planet 2004 TG10 and others
|Geminids||mid-December||Minor planet 3200 Phaethon|
|Ursids||late December||Comet 8P/Tuttle|
Extraterrestrial meteor showers Edit
Any other solar system body with a reasonably transparent atmosphere can also have meteor showers. For instance, Mars is known to have meteor showers, although these are different from the ones seen on Earth because the different orbits of Mars and Earth intersect orbits of comets in different ways. Because of the similar air pressure at altitudes for meteors only the relatively slower motion because of increased distance from the sun should marginally decrease meteor brightness. On March 7, 2004, the panoramic camera on Mars Exploration Rover Spirit recorded a streak which is now believed to have been caused by a meteor from a Martian meteor shower associated with comet 114P/Wiseman-Skiff. A strong display from this shower is expected on December 20 2007. Other showers speculated about are a "Lambda Geminid" shower associated with the Eta Aquarids of Earth (ie both associated with Comet 1P/Halley), a "Beta Canis Major" shower associated with Comet 13P/Olbers, and "Draconids" from 5335 Damocles.
See also Edit
- American Meteor Society (AMS)
- List of meteor showers
- North American Meteor Network
- Radiant, a point in the sky, from which (to a planetary observer) meteors appear to originate.
- Zenith Hourly Rate
- ↑ Jenniskens P., Meteor Showers and their Parent Comets. Cambridge University Press, Cambridge, U.K., 790 pp.
- ↑ Meteor Storms (Leonids)
- ↑ Marco Micheli, Fabrizio Bernardi, David J. Tholen (May 16, 2008). "Updated analysis of the dynamical relation between asteroid 2003 EH1 and comets C/1490 Y1 and C/1385 U1" (PDF). Retrieved on 2008-05-21.
- ↑ 4.0 4.1 Sekanina, Zdenek; Chodas, Paul W. (12/2005). "Origin of the Marsden and Kracht Groups of Sunskirting Comets. I. Association with Comet 96P/Machholz and Its Interplanetary Complex" (PDF). SAO/NASA ADS.
- ↑ Meteor showers at Mars
- ↑ Can Meteors Exist at Mars?
- ↑ Meteor Showers and their Parent Bodies
|Wikimedia Commons has media related to: Meteor showers|
- North American Meteor Network
- The International Meteor Organisation
- The American Meteor Society
- Meteor Showers Online , by Gary W. Kronk
- Meteor Showers, by Sky and Telescope
- Upcoming Meteor Showers, by Sky and Telescope
- Basics of Meteor Observing, by Sky and Telescope
- The Space Book by Eonitus
- Six Not-So-Famous Summer Meteor Showers Joe Rao (SPACE.com)
- Meteor Shower Photos and Info (AOL Research & Learn)
- Meteor Streams
- National Geographic News - Sky-Watcher Alert: Meteor Show Peaks This Week
- Infography about Meteor Showers
- Meteor showers Astronomy Cast episode #8, includes full transcript in PDF-format.