Motion of the Planets

• Planets move in two ways:

• They move in a path around the sun known as an orbit.

• They rotate on their axis – an imaginary line joining the north and south poles.

• The time taken for a planet to orbit the sun is known as a year.

• A year on Earth is approximately 365 days.

• The further a planet is from the sun, the longer its year. This is due to two factors:

• The further a planet is from the sun, the larger its orbit.

• The further a planet is from the sun, the smaller the effect of gravity, meaning the sun has less of a pull on the planet, resulting in a slower orbital speed.

• The time taken for a planet to rotate on its axis is known as a day.

• A day on Earth is approximately 24 hours.

• The rotational speed of a planet is largely determined by the initial rotational speed when the planet was formed. Therefore, the length of a day is unrelated to the size of a planet’s orbit, the orbital speed or the size of a planet.

Earth takes a day to rotate on its axis and a year to orbit the sun.

(Image: LuckySoul, Adobe Stock)

• The lengths of days and years for the eight major planets are shown in the table below (in Earth hours/days/years).

The lengths of days and years on the planets of our solar system