Meteors
From MariachiWiki
Contents |
Introduction
(by Mike Inglis)
A brilliant meteor, called a fireball, may weigh many kilograms, but even a meteor weighing less than a gram can produce a beautiful trail. Some of these visitors from space are large enough to survive (at least partially) their trip through the atmosphere and impact the ground as meteorites. Fireballs are sometimes followed by trails of light that persist for up to 30 minutes; some, called bolides, explode with a loud thunderous sound.
Question: how can a particle the size of a grain of sand produce such a spectacular sight?
Answer: the speed at which the meteoroid enters the Earth's atmosphere.
Many meteoroids travel at 60-70 kilometers per second. For comparison, the Space Shuttle moves around the earth at about 8 kilometers per second.
During its trip through the atmosphere, meteoroids collide with air molecules, knocking away meteor material [or ablating, as it is called] and ripping electrons from the meteor. When these same atoms recapture electrons, they emit light, the color depending on both the temperature and material of the meteor.
One can usually see a few meteors on any given night, at any location, at any hour. These are sporadic meteors. However, periodically there occur meteor showers, with hundreds of meteors emanating from the same apparent spot in the sky – the Radiant. These showers may last from a few hours to several days and are usually associated with comet paths, and the debris expelled by the comet.
One can make predictions as to the dates and times of many meteor showers, as they repeat every year when the earth passes through the path of a comet
Meteor observing is easy and great fun. Just choose a dark location, take something comfortable to sit on, lie back, and watch the show! Keen meteor observers go a step further and often use many different techniques to capture these swift moving objects: cameras to record the meteor trails, telescopes to find faint meteors, and radio telescopes to detect showers that may occur during the day!
Every day as many as 4 billion meteors, most miniscule in size, fall to Earth. Their total mass may be several tons, a large amount, but this is negligible when compared to the Earth's total mass of 6,600,000,000,000,000,000,000 tons.
Meteor Activity for August 2008
Shower of the Month: The Perseids
The Perseids, always the summer’s main attraction for meteor observers, are expected to peak around August 12d 09h UT, making the Monday night to Tuesday morning of Aug 11-12 probably the shower’s most productive in 2008. Good observed rates can be expected particularly in the early hours after the waxing gibbous Moon has set. Observers watching late on Aug 11-12 should experience increasing activity towards dawn: from a clear, dark location rates of a meteor per minute might be seen in the latter parts of the night as the shower radiant (near the Double Cluster on the Perseus/Cassiopeia border) climbs high into the eastern sky. Activity should be starting to decline by the time darkness falls on Aug 12-13. Moonlight becomes a nuisance after maximum, but even as late as Aug 13-14 it should still be possible to follow the Perseids’ immediate decline from peak, with at least a couple of hours of dark sky between moonset and dawn.
Perseid activity is evident as early as the third week of July. The main part of the shower, including its steady rise through the first 9 days or so of August, will enjoy dark skies. Activity takes a marked ‘kick’ around August 8-9, and watches between this date and August 14-15, particularly, should be very rewarding.
The Perseids are associated with Comet 109P/Swift-Tuttle, and are well known for the abundance of fast, bright meteors close to their maximum. Perseid meteoroids enter the atmosphere at a velocity of 60 km/sec, and the resulting meteors often leave behind persistent ionization trains.
The large numbers of bright events in the five-day interval centered on Perseid maximum makes this an excellent target for photography. Conventional film remains the medium of choice for most observers. Exposures, which can be with a static (undriven) camera, of 10-15 minutes’ duration, using ISO 400 film and a 50 mm or wide-angle 28 mm lens at f/2.8 or faster, can capture meteors of magnitude 0 and brighter. Ideal aiming directions are about 20-30 degrees to one side of the radiant at 50 degrees altitude above the horizon - Cygnus in early evening, the Square of Pegasus later in the night, or towards the north celestial pole, for example
Happy Observing!
Radio detection of meteors
There is an extensive scientific and engineering literature dealing with the subject of ionization trails produced by the passing of meteors through our atmosphere. The purpose of this summary is not to be as complete as possible, but to pinpoint several aspects that the writer thinks can be of use to the MARIACHI project. A pertinent study of bibliographical references has been made in the presentation of the MARIACHI project.......read the whole summary
Useful References for Radio Detection of Meteors
- FM Detection of Meteors by Marianne Gualtieri.
- International Meteor Organization
- American Meteor Society
- Nippon Meteor Society - Japanese Meteor Society.
Radar Meteor Date - Live!
This web site provides real time results from many commercial radar sites used to detect metors. The information is then used to provide data on atmospheric conditions.
