Re: how many miles would a rocket have to travel to leave our atmosphere

About 350 miles.

To learn more about the atmosphere on the web, try using the search terms

+atmosphere +earth

The web reference for this answer is

http:// liftoff.msfc.nasa.gov/academy/space/atmosphere.html

Thanks for your question.

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Admin note:
James Cotton provided the following additional answer:

Dear Sean,

This is not really my field, but seen as no-one else seems to have answered your question, i'll have a go. I think the answer to your question would depend on what part of the atmosphere you mean. As this diagram shows, molecules of gas from the atmosphere are still present 1,500 miles from the earth's surface, because the atmosphere isn't really a defined region - gas molecue is, however, 55 miles above the surface. Note, however, that escaping the earth's atmosphere isn't the same as escaping earth's gravity and entering orbit.

Hope that this answers your question,
Yours,
James