Astronomy

Understanding Meteor Showers the Pleiades the Perseid and more



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Simply explained: a meteor shower occurs when a large number of meteoroids collide with the Earth's atmosphere. They are caused when the orbit of Earth takes it through the fragments created from the waste of a comet. These pea sized fragments fall to earth at tremendous speed and burn up in the atmosphere. This is what gives us the shooting star effect' when we observe the short white trails that appear in the night sky and is known as a meteor. A really bright meteor will leave a persistent trail.

Occasionally these fragments can be quite large and a piece of meteoroid may make it to the Earth's surface without completely burning up from the friction. This is known as a meteorite. From the study of the meteorites found on Earth experts have managed to find out many things about the composition of comets and other interstellar material.

Although these fragments that burn up in the earth's atmosphere are only approximately between 1mm and 1cm in diameter, the degree of light they generate in their demise is astonishing. The reason for this is because of the immense speed that they travel at just before they hit the earth's atmosphere. The average speed is 71 kilometers per second or the equivalent of going around the Earth in 3.8 minutes!

Most people assume that meteors give a white light, in fact they can be of many hues. The reason for this is that meteors contain differing elements and when they heated to a certain temperature will emit different colors as an indication of their composition. For example, sodium gives off an orange/yellow hue, iron shows up as a yellow light, magnesium as a blue/green light, a violet hue could indicate calcium atoms and silicon atoms and atmospheric nitrogen molecules will show up as a red light.

Ordinarily you cannot hear sounds from a meteor, so you will only see a meteor if you happen to be looking in the right place at a certain time. However, it has been reported by some people that the extremely bright meteors have emitted a hissing sound. An explanation for this could be due to low frequency radio waves interfering with the environment. On rare occasions a sonic boom will accompany the really bright fireballs and can be heard as a distant rumble.

The first anecdotal account of a meteor shower was in 902 when Chinese, Egyptian and Italian observers reported seeing what is known now as a Leonide' storm, describing how the the "Stars fell like rain" Many more similar worldwide accounts would pepper history thereafter.

In 1833 the meteor storm was so intense that it led to the beginnings of a hypothesis on the formation and origins of meteors.

Agnes Clerke, the influential Victorian astronomy writer wrote in 1833 that on November 12th to the 13th "a tempest of falling stars broke over the Earth" she likened their fall to about half as much as the frequency of the flakes of snow in a thunderstorm and finishes: " it was computed, on the basis of that much-diminished rate, that 240,000 must have been visible during the nine hours they continued to fall."

Meteor showers still continue to fascinate and fill people with wonder.There can be up to 7 or eight regular meteor showers every year and scientists are still collating data about their composition and trajectories, and are discovering new insights regularly.
For example did you know scientists believe that a giant meteorite hit the earth about 70 million years ago destroying nearly all the life on Earth? Just 10% of all Earth species were said to have survived with the dinosaurs being the biggest casualty of the global disaster.

sources: http://leonid.arc.nasa.gov/history.html http://www.nitesky.org/Newsletters/fall2002.html

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