The Birthday of Edmond Halley (1656) – Halley’s Comet

Halley used Newton’s laws to predict the return of the comet named after him. He modelled the comet’s orbit as an ellipse (eccentricity 0.967) with period about 76 years. The mathematics of orbit determination requires solving Kepler’s equation: M = E – e sin E, where M is mean anomaly, E is eccentric anomaly. Halley’s work was the first demonstration that comets are periodic, not divine omens. The comet’s last appearance was 1986; next is 2061. Orbital mechanics turned a mystery into a calendar event.