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Meteor shower

2007 Schools Wikipedia Selection. Related subjects: Space (Astronomy)

   A meteor shower, also known as a "meteor storm," is a celestial event
   where a large number of meteors are seen within a very short period of
   time. These meteors are small fragments of cosmic debris entering
   Earth's atmosphere at extremely high speed, leaving a streak of light
   that very quickly disappears. Most of the small fragments of cosmic
   debris are smaller than a grain of sand, so almost all fragments are
   burnt up and never hit the earth's surface. Fragments which do contact
   earth's surface are called meteorites.

The Causes of Meteor Showers

   Each time a periodic comet swings by the Sun, it produces large amounts
   of small particles which will eventually spread out along the entire
   orbit of the comet to form a meteoroid "stream". If the Earth's orbit
   and the comet's orbit intersect at some point, then the Earth will pass
   through this stream for a few days at roughly the same time each year,
   producing a meteor shower. The parent bodies (comets) of most known
   meteor showers have now been identified.

   Ronald A. McIntosh of Auckland, New Zealand has offered apparently the
   first idea of a meteoroid stream or trail in the 1950's where meteroids
   freed from the comet, traveling at low speeds relative to the comet,
   drift mostly in front of or behind the comet. However after that the
   pattern becomes complex and changing in detail even if the overall
   structure remains the same.

   Robert McNaught and David Asher among others have attempted to
   characterize a meteor stream which is responsible for a storm as
   opposed to a shower:

   A cloud of meteoroids are released from the comet in a roughly
   spherical distribution. The first effect is simple orbital mechanics -
   the material drift little laterally away from the comet while drifting
   ahead or behind the comet forming something of a trail of meteoroid
   with more or less dense zones from repeated revolutions of the comet
   through the neighbourhood of the Sun. The second effect is that the
   orbits of most repeating comets, and materials leaving them are in
   resonant orbits with Jupiter - 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 over many revolutions it will tend
   to pull meteoroids into keeping that relative position. So the trail
   has a clumping, a braiding or a tangling of crescents, or filaments of
   each individual release of material. The third effect is that of light
   pressure which will tend to push small objects, about the size of
   meteoroids, away from the Sun - exactly countering the effect of the
   Suns gravity to a small degree while larger objects (responsible for
   bolides or fireballs will tend to not be affected by light pressure.

Meteor Showers originate from fixed points in the sky

   Because meteor shower particles are all traveling in parallel paths,
   and at the same velocity, they will all appear to radiate from a single
   point in the sky to an observer below. 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 they appear to originate.

Famous Meteor Showers

   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 though when not storming it's less active than the
   Perseids.

Extraterrestrial Meteor Showers

   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. 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, although it is unlikely that Spirit or
   Opportunity will still be operational at that time to observe it.

   Retrieved from " http://en.wikipedia.org/wiki/Meteor_shower"
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