Meteor Section

Meteor shower and sporadic meteors

The English version. The Norwegian version.

Once a year, more precicely on August 12., the Earth enters the dust cloud of Comet Swift Tuttle. Tens of meteors an hour seem to radiate from the constellation Perseus. The finest meteors show colours such as green, yellow or red. Many meteors have persistent trains, and the brightest can cast a shadow on the ground.

 [Meteorsverm]

49K GIF. In a meteor shower, the meteors seem to radiate from a small area in the sky.

By T.E.Hillestad - translated by L.T.Heen

Similar events occur throughout the year, for instance on some days near December 13th and January 4th. What is the cause of this phenomenon?

Showers of meteors

The Meteor showers are mainly dust particles from comets that have disintegrated. The particles move in almost parallell paths, and when they hit the atmosphere, they seem to radiate from a point in the sky. This point is called the radiant of the shower.
   Something similar happens when you drive a car through driving snow. We know that the snow flakes move quite parallell to each other, but to the driver the snow flakes seem to radiate from a point ahead of the car.
   There are many different meteor showers. Some last for weeks, while others can be seen for a few days only. There is a big difference in the number of meteors per hour, and in the brightness of the meteors. You'll get more information on the various meteor showers below.

Meteor storms

If the cometary material is evenly distributed around the (old) cometary orbit, the shower will be equally strong every year. But on rare occasions the Earth enters areas with much higher dust density. When this happens, the meteor activity can increase to thousands per hour.
   There are many descriptions of such events in the past. The most famous of all meteor storms is The Leonids which were very active in 1799, 1833, 1866 and 1966 (the storm has returned with thousands of meteors in 1999, watch out for more to come!). Other well known storms are The Draconids in 1933 and 1946, and The Andromedids in 1872 and 1885.
   There are many other examples of showers that were more active when the "mother comet" was in a certain position in its orbit relative to the Earth, among them The Perseids in 1861, 1862 and 1990-, The Lyrids in 1982, and The Ursids in 1795, 1945 and 1986.

Sporadic meteors

Some meteors doesn't belong to any known shower. These are the sporadic meteors, which appear randomly across the sky. On a dark night you may see around 10 sporadic meteors per hour.
   You see twice as many sporadic meteors in the morning as you do in the evening. This is due to us being on the "front" of the Earth. Therefore we see both the meteors coming towards us, and the meteors the Earth catches up with in its race around the Sun.
   Another analogy from car driving : Insects always smash into the front window of the car not the back window, even though the air is full of them.
   There is also a sesonal variation in the sporadic meteor activity. The best sporadic months are in the fall (especially August and December-January) while in the spring the sporadic activity is comparatively low. The reasons for this are complicated.

Read more about:

Radiant-catalogue (International Meteor Organization)
What will be visible this year ? (International Meteor Organization)
Description of the various meteor showers (Gary Kronk)

Background - meteors and their origin:

    [Meteors - review, definitions] [Origin of asteroids and comets] [Comets] [Origin of meteors] [Physical description of the meteor phenomenon] [Meteor showers and sporadic meteors]

Background - meteorites and craters:

    [Meteorites - review] [Localization of a meteorite fall] [Identification of meteorites] [Norwegian meteorites] [Asteroid- and cometary collisions] [Cosmic explanation of mass extinction ?] [The making of a meteorite crater] [Craters in the Nordic Region]

General:

    [Observations] [Results] [Meteor Section] [NAS] [Web]

Last modified: Thu Jan 11 09:38:50 MET 2000 by Lars Trygve Heen.