MadSci Network: Astronomy

Re: How did Newton find the distance from the earth to its moon?

Date: Mon Nov 30 12:21:26 1998
Posted By: Nick Steph, Faculty, Physics, Franklin College
Area of science: Astronomy
ID: 911953728.As

The distance to the Moon could be determined from a measurement of 
parallax.  If the Moon is observed by two people separated by about 420 
miles, the position of the Moon, with respect to the fixed stars, will vary 
by about one-tenth of a degree.  Although this sounds small, it can be 
discerned by the naked eye and measured quite precisely with the use of 
telescopes.  If the two data mentioned above were the the actual 
measurements, then the distance to the moon would be given by:
D = (420 miles)/sin(0.1 degree) =  240,642 miles.

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