Elliptical Orbit Pull

A satellite follows an ellipse because gravity always pulls it toward the planet at one focus. Its speed changes along the orbit, so it sweeps equal areas in equal times.

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Age 17: open this week

In the picture

The planet sits at one focus of the orbit.
The satellite moves along the ellipse.
The arrow shows the gravitational pull toward the planet.
The shaded wedge marks an area swept out in a time interval.

Examples

The Moon orbiting Earth
A comet looping around the Sun

Key takeaways

Gravity bends the satellite’s path into an ellipse with the planet at one focus.
Equal areas in equal times is Kepler’s second law.

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