The speed of a planet in its orbit varies in its journey around the sun .

Question

(a) at what point in its orbit is the planet moving the fastest . (b) at what point is it moving the slowest .

Answer 1

For a satellite of the Earth, the Apogee is the point of its orbit when it is farthest from the Earth, and the Perigee is the point of its orbit when it is closest to the Earth.

For a satellite of a body that is not the Earth, the general terms are Apoapsis and Periapsis.

For a satellite of the Sun, the terms are Aphelion and Perihelion.

 

Kepler's 2^nd Law of Planetary Motion dictates that a planet's fastest speed is at Perihelion and its slowest at Aphelion.

 

[Kepler's 2^nd Law of Planetary Motion: A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.]

Answer 2

A planet in a star system generally follows an elliptical orbit; the planets move around in the shape of an oval. When a planet is closest to the Sun during its orbit, it is moving fastest. The planet's orbit moves slower the farther away it is from the Sun.