By shashank; Published 09 Dec 2007
Johannes Kepler performed an experiment to calculate the distance between earth and mars, and hence he managed to find out the distance between the sun and mars in terms of the distance between sun and earth.
the experiment is as follows :
on the day of opposition of mars, two photographs of mars are taken 12 hours apart, once when it is setting i.e. when the sun is rising, and the other, when mars is rising, i.e. when the sun is setting. the two photographs are then compared for change in apparent position of mars. Surprisingly enough, the change in the apparent position is big enough to be detected even in amateur telescopes. the apparent shift is in the order of arc minutes!! ( 30 arc minutes = apparent diameter of full moon). now, this shift can be used to find out the distance between earth and mars using the parallax method.
(for more info on parallax, check this link : http://en.wikipedia.org/wiki/parallax)
instead of using the earth's orbit as the base of the triangle, if the diameter of the earth is used as the base, then the distance to mars can be calculated by the way shown in that link...
this year, mars is at opposition on 24th of december .. so all those of you who have tracking equipment and cameras, do capture mars on the morning and evening of 24th.. and we can perform kepler's experiment all over again...