= Owen Gingerich
{c}
An astronomer and historian who reconstructed the quantitative reasoning behind early <celestial mechanics>. His analysis of <Johannes Kepler>’s difficulty predicting the position of Mars shows why the observer’s own <orbit> matters: correcting the model of Earth’s motion changes the inferred position of another planet. Repeated observations separated by a Martian year allowed Kepler to compare Earth’s position from different viewing directions, exposing an error in the assumed terrestrial <orbital eccentricity>.<The great Martian catastrophe and how Kepler fixed it by Owen Gingerich>[Printed pp. 52–53 and Fig. 4: Earth-orbit correction and observations separated by 687 days]{ref}
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