Introduction
Cosmic Rulers
Planetary Planarity
Radial Velocity Technique
Target: Gamma Cephei
Other Targets
Tools of the Trade

Extrasolar Planets, Radial Velocity, and Astrometry

Up a Tree with a Radar Gun

From your new vantage point, as the adult and and the child move up and down on the see-saw, sometimes the adult is speeding toward you, sometimes away from you.

illustration of two people on a seesaw with a third person in a tree above them

From a great distance, however, you can’t tell whether the person on the other end of the teeter-totter is a child or another adult (below). But you can still measure the speed of the adult. If you know how far away they are, and if you can measure the distance of the adult from the fulcrum, you can determine whether the person on the other end of the teeter-totter is an adult or a child.

illustration of one person sitting in a tree

So what does this have to do with planets around other stars?

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