Current velocities of planets?

  1. Alkatran

    Alkatran 944
    Science Advisor
    Homework Helper

    I'm writing up a simple simulation of the solar system for my computer simulations in physics class, which you can see at (java applet)

    Now, I have the correct position data for the planets thanks to a website giving them relative to earth for telescope users. What I need is the velocity of the planets now.

    Where can I find this? Do I have to just plot the positions over time and figure it out using math?
  2. jcsd
  3. russ_watters

    Staff: Mentor

  4. tony873004

    tony873004 1,594
    Science Advisor
    Gold Member

    Write an e-mail to JPL Horizons system asking for the positions and velocities of any solar system object relative to any other solar system object at any given time. Use the template below. Make sure that your STOP TIME is 1 s after your START TIME.
    Center = '@###'
    Command = '###'

    Center is the object you're referencing your positions and velocities against. Command is the object you want data for.

    ID's: 199 = Mercury, 299 = Venus, 399 = Earth... 999 = Pluto, etc.
    301 = 1st Moon of Earth, 401 = 1st Moon of Mars, 402 = 2nd moon of Mars, etc.
    010 = Sun

    So for example, the following e-mail asks for Mercury's (199) position and velocity relative to the Sun (010)

    Address the e-mail to
    Put the word job in the subject line.
    Code (Text):
    START_TIME = '2006-Mar-13 17:30:58'
    STOP_TIME = '2006-Mar-13 17:30:59'
    TABLE_TYPE = 'Vector'
    REF_PLANE = 'Ecliptic'
    CENTER = '@010'
    JPL's response e-mail, usually instant, gives you lots of data. Search for this:

    Code (Text):

    2453808.229837963 = A.D. 2006-Mar-13 17:30:58.0000 (CT)
      [b]-5.730179611929864E+07  1.963895677831354E+06  5.419068833578369E+06
      -1.179887453107446E+01 -4.658790336366766E+01 -2.723342317439528E+00[/b]
       1.921027750084662E+02  5.759096310840907E+07  9.894693725010404E+00

    Notice the 6 numbers I've highlighted. They are the x,y &z positions of Mercury with respect to the Sun, and the x,y,& z velocities of Mercury with respect to the Sun. The 8th of those 9 numbers is the actual Mercury/Sun distance, which you can also compute with d2=x2+y2+z2
  5. Alkatran

    Alkatran 944
    Science Advisor
    Homework Helper

  6. Alkatran

    Alkatran 944
    Science Advisor
    Homework Helper

    That is FANTASTIC. Thank you!
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