Extrasolar Planets, Radial Velocity, and Astrometry
Two Adults on a Teeter-Totter
Here's what you would see if two adults were playing on the teeter-totter:
Notice that both participants are now moving up and down at the same speed. The adult on the left had to move farther from the fulcrum to balance the adult on the other end.
Now suppose the only information you had about the two people on the teeter-totter was how fast the adult on the left was going?
How could you measure the speed of the adult? Wrap him in tinfoil and use a radar gun!
If you stood beside the teeter-totter, say 10 feet from the fulcrum, your radar gun would detect no speed for the adult in tinfoil because all of the adult’s motion is up and down.
So how can you measure motion towards or away from you? Climb a tree!
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Copyright ©2009 McDonald Observatory. This material is based upon work supported by the National Aeronautics and Space Administration under Grant/Contract/Agreement No. HST EO 11210.08 issued through the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.