Space Forum / Astronomy / January 2005

There are people who know a lot more about history than I do, so
perhaps someone will correct me.  As I understand it, Tycho Brahe
measured the positions of visible planets for many years.  These
would have been right ascension and declination (or possibly ecliptic
longitude and latitude) at the times of observation.  I think his
instrument was probably a transit circle.

The observations themselves were just positions in the sky.  Kepler's
theory had to account for the changing position of Earth in order to
explain the observations.

Kepler used Tycho Brahe's measurements with various mural transit
instruments, so effectively Tycho obtained Declination and Right Ascension,
which could easily be converted to ecliptic coordinates of celestial
latitude and longitude (I say easily, but this routine calculation was
difficult enough because it all had to be done with paper and pencil).  By
(in essence) using observations of Mars that were one sidereal martian year
apart, the actual position of Mars could be calculated by triangulation from
the two different positions of Earth.  With many pairs of observations the
shape of the orbit could be determined to be an ellipse.  There are a lot of
additional details but that's the principle of the method.

Where could I find out more of these details?

Thanks,

Ted

Mike Dworetsky wrote:

over

then

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Ascension,

was

pencil).  By

martian year

triangulation from

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lot of