Orbital revolution

Orbital revolution is the movement of a planet around a star, or a moon around a planet. For example, the Earth revolves around the Sun, and the Moon revolves about the Earth.

Planets and moons revolve in elliptical orbits. One orbital revolution of a planet takes one year, while a revolution of the Moon takes a month.

Astronomers usually use different words for the orbit of a planet around a star, and for the spin of a planet about its own axis. If an item is in orbit, it is "revolving", while the spin of a planet is called "rotating". The amount of time it takes for an object to revolve around the Sun is a year, and the amount of time it takes to revolve around its axis is one day. According to the Gregorian calendar, a year on Earth is equal to 365 days, with an extra day added every four years.

The amount of time it takes for an object to move around the sun is different for every object. For example, it takes the planet Mercury about 88 days to revolve around the sun, but it takes the dwarf planet Pluto over 248 years to revolve around the sun.

Category:Astronomy