Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calculation of a planet's mass via wavelengths

  1. Oct 11, 2011 #1
    I gotta find an answer or a push to the right tracks on this question.

    Suppose a spacecraft is in a circular orbit about a distant planet. the spacecraft emits a continuous radio signal with a wavelength of 6m. The signal's wavelength varies between 5.99969m and 6.00031m; the period of variation (full period of wavelength) is 5 hours. What is the mass of the planet? Assume that you are located in plane of the spacecraft's orbit and knowing that circumference is 2piea (a = radius) and that speed = distance / time.

    Thanks in advance!
  2. jcsd
  3. Oct 11, 2011 #2
    I believe this requires kepler's 3rd law (where the common focus is in the distant planet).
  4. Oct 12, 2011 #3
    That's a good idea. You can also use Newton's law of gravitation. Now you have to include the given frequencies. Do you know a relationship between velocity and frequency shift?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook