# Current velocities of planets?

1. ### Alkatran

944
I'm writing up a simple simulation of the solar system for my computer simulations in physics class, which you can see at myweb.dal.ca/cr376499 (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?

3. ### tony873004

1,588
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)

Put the word job in the subject line.
Code (Text):
!$$SOF EMAIL_ADDR='' START_TIME = '2006-Mar-13 17:30:58' STOP_TIME = '2006-Mar-13 17:30:59' TABLE_TYPE = 'Vector' REF_PLANE = 'Ecliptic' CENTER = '@010' COMMAND='199' !$$EOF

JPL's response e-mail, usually instant, gives you lots of data. Search for this:

Code (Text):

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

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

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5. ### Alkatran

944
That is FANTASTIC. Thank you!