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Author Topic: Epoch  (Read 6800 times)

atomic7732

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Epoch
« on: August 27, 2009, 05:18:36 PM »
What epoch does US use? The default on neo.jpl?

That's: [epoch=2006- 12-01.0] 16

http://neo.jpl.nasa.gov/
http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=106P&orb=1
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Dan Dixon

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Re: Epoch
« Reply #1 on: August 27, 2009, 05:25:29 PM »
I'm not entirely certain what you're asking...

But for Dec RA numbers they are all J2000 based.

http://en.wikipedia.org/wiki/Epoch_%28astronomy%29#J2000.0

Is that what you mean?
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atomic7732

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Re: Epoch
« Reply #2 on: August 27, 2009, 05:28:48 PM »
If you go to the second provided link and look above orbit parameters, there is an epoch dropdown. Is J2000 the same as 2006-12-01.0? You need epoch same for M right?]
Though if I look at Ciffreo, it gives me a 2007-08-01.0 epoch date.
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Dan Dixon

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Re: Epoch
« Reply #3 on: August 27, 2009, 08:50:07 PM »
I'll claim minor ignorance on this... so someone please correct me if I'm wrong.

I think that the Epoch it's talking about is the associated date/time where those orbital elements are based.


If you're wanting to add various comets and asteroids into Universe Sandbox do this:

Click on this Horizon System link just about the applet:
http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=106P%20[1999]

Make these changes:

Ephemeris Type = 'Vector Table'

Coordinate Origin = @sun

Under Table Settings Change:
output units = km & km/s

Change time span to:
start = 2008-01-01
stop = 2008-01-02

For this comet it should look like this:
Code: [Select]
Ephemeris Type [change]   :  VECTORS
Target Body [change]      :  Comet 106P/Schuster [1999] (SAO/1999)
Coordinate Origin [change]:  Sun (body center) [500@10]
Time Span [change]        :  Start=2008-01-01, Stop=2008-01-02, Step=1 d
Table Settings [change]   :  output units=KM-S
Display/Output [change]   :  default (formatted HTML)
Press the Generate Ephemeris button.

Find this section in the output results:
Code: [Select]
*******************************************************************************
JDCT
   X     Y     Z
   VX    VY    VZ
   LT    RG    RR
*******************************************************************************
$$SOE
2454466.500000000 = A.D. 2008-Jan-01 00:00:00.0000 (CT)
  -3.696330150114028E+08  1.876239664454978E+08  1.481976483689495E+08
  -1.651474509485226E+01 -9.403602827061283E+00  2.488145223257269E+00
   1.468416667434924E+03  4.402202420984842E+08  1.069644369078651E+01
2454467.500000000 = A.D. 2008-Jan-02 00:00:00.0000 (CT)
  -3.710577443435432E+08  1.868104099691846E+08  1.484117649337029E+08
  -1.646512075064017E+01 -9.428678541826788E+00  2.468272783599756E+00
   1.471498000230135E+03  4.411440024310767E+08  1.068688672266089E+01
$$EOE
*******************************************************************************
The numbers you want are the 1st two lines of 3 numbers each:
Code: [Select]
 -3.696330150114028E+08  1.876239664454978E+08  1.481976483689495E+08
  -1.651474509485226E+01 -9.403602827061283E+00  2.488145223257269E+00
This is the x,y,z position and x,y,z velocities for that body at that date.

Copy those numbers into your XML file and make it look like this:
Code: [Select]
<PositionX>-3.696330150114028E+08</PositionX>
<PositionY>1.876239664454978E+08</PositionY>
<PositionZ>1.481976483689495E+08</PositionZ>
<VelocityX>-1.651474509485226E+01</VelocityX>
<VelocityY>-9.403602827061283E+00</VelocityY>
<VelocityZ>2.488145223257269E+00</VelocityZ>
You can drop these values into any of the "Our Solar System" simulations since they all use this date (January 1, 2008).

Let me know if you need more help.


If you want to do more than 5 or 6 of these there's a hidden feature in Universe Sandbox to automate the extraction of this data into the XML format. Let me know and I'll share the instructions.
« Last Edit: August 27, 2009, 08:54:58 PM by Dan Dixon »
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atomic7732

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Re: Epoch
« Reply #4 on: August 28, 2009, 04:36:17 PM »
Please Share! I want to do some named Apollos!
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Dan Dixon

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Re: Epoch
« Reply #5 on: August 28, 2009, 08:11:25 PM »
Here's how to automatically extract data from NASA's Horizon System:
http://universesandbox.com/forum/index.php/topic,722.0.html
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atomic7732

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Re: Epoch
« Reply #6 on: August 29, 2009, 01:53:30 PM »
???
Code: [Select]
<Body>
<Name>8P/Tuttle</Name>
<Object>Asteroid</Object>
<PositionX>-1.260127611301537E+08 km</PositionX>
<PositionY>-5.500024336231098E+08 km</PositionY>
<PositionZ>-1.845398373426739E+08 km</PositionZ>
   <VelocityX>2.576999872849103E+00 km/s</VelocityX>
<VelocityY>-1.650222804626428E+01 km/s</VelocityY>
<VelocityZ>3.535349409995463E+00 km/s</VelocityZ>
</Body>
Code: [Select]
<Body>
<Name>8P/Tuttle</Name>
<Object>Asteroid</Object>
<PositionX>-126012761.1301537 km</PositionX>
<PositionY>-550002433.6231098 km</PositionY>
<PositionZ>-184539837.3426739 km</PositionZ>
    <VelocityX>2.576999872849103 km/s</VelocityX>
<VelocityY>-16.50222804626428 km/s</VelocityY>
<VelocityZ>3.535349409995463 km/s</VelocityZ>
</Body>
« Last Edit: August 29, 2009, 02:04:58 PM by NeutronStar »
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atomic7732

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Re: Epoch
« Reply #7 on: August 29, 2009, 02:06:32 PM »
No bother. I fixed it. can you use the E+08? Or whatever? Or no? I figured out that km/s was just km since it's in the velocity tag. :)
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Dan Dixon

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Re: Epoch
« Reply #8 on: August 29, 2009, 03:04:06 PM »
Quote from: NeutronStar on August 29, 2009, 02:06:32 PM
can you use the E+08?

Yes.

Quote from: NeutronStar on August 29, 2009, 02:06:32 PM
I figured out that km/s was just km since it's in the velocity tag. :)

If you leave off the units it defaults to km and km/s.

You can use the numbers as written by JPL's Horizon system without any modification.
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atomic7732

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Re: Epoch
« Reply #9 on: August 29, 2009, 03:05:20 PM »
If I would have known...  ;D ;D
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Dan Dixon

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Re: Epoch
« Reply #10 on: August 29, 2009, 04:12:35 PM »
If you're having problems it's always a good idea to check the Sandbox Log.txt file. It reports loading errors like encountering units that it doesn't understand.

I'm planning to do a better job of reporting errors like this to the user in version 2 (like it will come up in an on screen text box or something similar).

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