MadSci Network: Astronomy
Query:

Re: Why doesn't the Earth's orbit around the sun decay?

Date: Fri Apr 21 16:03:54 2000
Posted By: Enrico Uva, Secondary School Teacher Chemistry, Physical Science
Area of science: Astronomy
ID: 953085274.As
Message:

Once in motion, a body keeps moving unless an external force acts on it. 
In the case of a satellite, its orbit eventually decays because at the 
distance that the satellite circles the earth ( only 36000 km) , there are 
still enough molecules to gradually slow it down. Of course the 
satellite's small mass makes it vulnerable to this effect. But with a much 
larger mass such as a moon or planet, the effect is much smaller 
especially since they encounter far less particles in the near-vacuum of 
space. The occasional cometary and asteroid debris are exceptions, but 
they are still of insignificant mass compared to that of the earth.

Enrico Uva


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