Study the different ways of defining a year - a tropical year, a sidereal year, and the anomalistic year

© Open University (A Britannica Publishing Partner)

Learn about the length of both a year and a day on Mercury.

Encyclopædia Britannica, Inc.

Isaac Newton's formulation of the law of universal gravitation.

Adapted from C.R. Scotese, The University of Texas at Arlington

A time-lapse representation of Earth changing through geologic time, from the late Proterozoic Eon (c. 650 million years ago) to the projected period of Pangea Proxima (c. 250 million years from now).

Encyclopædia Britannica, Inc.

Learn about carbon dioxide and its relationship to warming conditions at Earth's surface, as explained by John P. Rafferty, biological and Earth sciences editor of Encyclopædia Britannica.

Contunico © ZDF Studios GmbH, Mainz; thumbnail © Volodymyr Shevchuk/Dreamstime.com

Overview of water tides.

Encyclopædia Britannica, Inc.

Earth's rotation on its axis and its revolution around the Sun.

© MinuteEarth (A Britannica Publishing Partner)

The role that Hadley cells play in determining the geographic extent of tropical rainforests and deserts.

Encyclopædia Britannica, Inc.

Scale of the universe.