The path that planets take around the sun is called it's orbit. The gravitation pull of the sun keeps each planet in it's orbit. Each planets orbit varies in the time it takes to make one trip around the sun.
A planet is slowest when farthest from the Sun.
A planet moves fastest when closest to the Sun
When a planet makes one complete rotation around the sun is called a revolution, and an orbit. When it spins on it's axis then it is called a rotation.
It depends on their mass and their distance from the sun
Orbital velocity
An elliptical orbit.
It is called its orbit.
An "orbit"
mars
A planet in an elliptical (oval) orbit will move faster as it gets to its closest point to its sun, and slow down as it reaches its furthest point. A planet with a truly circular orbit will have a constant speed.
Distance from the Sun. (The closer it is, the faster it moves.)
If a satellite is in an elliptical orbit around the Earth, the Earth will be at one of the focii. The speed of the satellite will then constantly be changing. It will move the fastest when it is nearest to the Earth (perigee) and slowest when it is furthest away (apogee).
This was worked out by Kepler about 400 years ago. Kepler's second law of planetary motion shows how a planet moves faster when it's nearer, in its elliptical orbit, to the Sun. Kepler's third law relates the time a particular planet takes to orbit the Sun to its average distance from the Sun. A planet which is farther from the Sun has a slower orbital speed than a planet closer to the Sun.
Velocity is a indication of speed and direction, so the fact they travel around it means that the direction is continually changing and, therefore velocity is continually changing. Kepler was the astronomer who discovered the laws of motion for the planets. Newton, a century later, derived the laws from his laws of gravity and motion. The first law of planetary motion states that planets orbit the sun in an elipse. So the speed is continually changing.
A satellite in a closed orbit has the greatest speed when it's closest to the planet, and the lowest speed when it's farthest from the planet.
I'll assume you mean: "... as opposed to a circular orbit". That is caused by the fact that for a circular orbit, a planet needs a VERY PRECISE SPEED. Change the speed slightly (at a particular point in the orbit), and the orbit immediately becomes elliptical.
in the orbit of a planet there is a point called perihelion which is closest point to the sun and aphelion which is furthest from the sun . Moment of a planet in it's elliptical orbit reaches it's maximum in perihelion
A planet in an elliptical (oval) orbit will move faster as it gets to its closest point to its sun, and slow down as it reaches its furthest point. A planet with a truly circular orbit will have a constant speed.
Kepler's Second Law: The planet moves faster when it is closer to the Sun.
A planet has an elliptical shaped orbit. It orbits with a constant angular speed, but a varying linear speed.
A satellite in an elliptical orbit gains speed as it draws closer to the central body and loses speed as it moves farther away from the central body.
A comets orbit is elliptical and goes into the depth of the solar system and speed up when it goes around the sun
The mass of the Sun and the distance between the planet and Sun. As the Sun's mass is (more or less) constant, all we need to know is the distance. Technically this is called the "semi major axis" of the elliptical orbit. (If you wanted to be really, really accurate the mass of the planet does have a very very small effect.)
As the planet approaches perihelion (point of nearest approach to the Sun), its orbital velocity gets faster, and it is fastest at perihelion. Similarly, at aphelion (point of furthest approach to the Sun), the orbital velocity is slowest.
Distance from the Sun. (The closer it is, the faster it moves.)
To be in a perfect orbit around the Sun, maintaining always the same distance, at a specific distance a planet would need a very specific speed. Since it is unlikely that it just happens to have the correct speed, it will move around the Sun in an ellipse instead.