All Questions
4 questions
2
votes
0
answers
323
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How the heck does JPL actually do the numerical integration for their development ephemerides? (general questions)
After writing this answer to JPL Horizons - "highly accurate measurements of planetary positions" - how do they do it? which draws from Park, Folkner, Williams & Boggs 2021 The JPL ...
- 30.7k
3
votes
3
answers
297
views
Calculating velocity of Earth from JPL DE
We have discussed how to calculate positions from JPL development ephemerides in this question.
Following this answer, I am now using SPICE's algorithm for calculating the derivatives of the Chebyshev ...
- 371
3
votes
1
answer
136
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For how many solar system bodies do recent JPL Development Ephemerides include libration?
Since the Earth and the Moon are so gravitationally and tidally engaged and the laser ranging data so precise, the JPL Development Ephemerides are based on extensive modeling of the Earth-Moon system ...
- 30.7k
19
votes
2
answers
3k
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Why does the Earth have a z-component at the start of the J2000 epoch?
When I go to the NASA HORIZONS webpage
https://ssd.jpl.nasa.gov/horizons.cgi
and ask for the VECTOR coordinates of the Earth on 1 January 2000, it tells me that Earth has the following coordinates ...
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