When was Halley's comet last seen?

When will Halley's comet reappear?

The Halley's comet appears after every

The Halley's comet appears after every

The orbit of Halley's comet is an ellipse 36.18 astronomical units long and 9.12 astronomical units wide. Find its eccentricity.

Classify the following motions as periodic and non-periodic motions? (a) Motion of Halley's comet. (b) Motion of clouds. (c ) Moon revolving around the Earth.