Filed under
orbit
6 milestones, in chronological order.
- c. 150 CEAncient Eyes
Ptolemy's equant makes Mars predictable
To fit Mars, Ptolemy let it sweep its circle at a steady rate around a point that was not the centre — a cheat that broke Greek doctrine and worked for 1,400 years.
- 499 CEAncient Eyes
Aryabhata fixes Mars's year to within half an hour
The Aryabhatiya assigns Mars 2,296,824 orbits per 4,320,000-year cycle. Work it through with his own day count and the period is 686.9997 days; the modern value is 686.98.
- 877–1375 CEAncient Eyes
Islamic astronomers take the equant apart
Al-Battani re-measured every planetary motion, Ibn al-Haytham argued the equant was physically impossible, and Ibn al-Shatir built the models Copernicus would mirror.
- 1543Ancient Eyes
Copernicus explains Mars's backwards loop
De revolutionibus turned Mars's retrograde loop into a trick of perspective — Earth overtaking it on the inside. The predictions were no better than Ptolemy's.
- 1609The Telescope Era
Eight arcminutes of Mars break the perfect circle
A stubborn eight-arcminute gap between Tycho's Mars positions and every possible circular orbit forced Kepler to the ellipse, and rebuilt astronomy around it.
- Every 779.9 days — windows in 2026, 2028–29 and 2031The Road AheadPlanned
The 26-month clock that governs everything
Earth and Mars line up for a cheap transfer once every 779.9 days. A six-week hardware delay does not cost six weeks; it costs more than two years.