Questions tagged [ephemeris]

Questions about the predicted positions of an object in space, like another planet, comet, or asteroid.

11 questions with no upvoted or accepted answers
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Callisto's orbit: circular vs JPL is periodic 4 degree error, why?

I am approximating the azimuthal angle of Callisto from Jupiter or the Jupiter+moons barycenter using a constant angular speed circular orbit. This differs from the JPL ephemerides by only about 4 ...
• 260
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Search satellite locations on the sky by date and coordinates

I would like to know what satellites, asteroids, comets, etc passed through a certain coordinate or region on the sky at a certain date. I have found sites like NASA's HORIZONS, but this searches for ...
• 51
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Did the Juno mission locate Jupiter at the same precision as Saturn (4 km)?

Juno's low perijove should be great for measuring Jupiter's gravitational effect on Juno's orbit. Cassini together with VLBI has measured Saturn's location to within 4 km. Will Was Juno be able to ...
• 10.9k
219 views

Trying to find the source of these three orbital elements

I'm working through section 65 “Calculating the Moon's position” in Practical Astronomy with your Calculator or Spreadsheet (fourth edition) by Duffett-Smith and Zwart. They begin the calculations ...
• 585
134 views

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 ...
• 31.8k
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Planets orbit fitting

I would like to fit planets orbits. To do this, I need a set of mock observations. I can get them from right ascension/declination obtained from the Horizons interface: EDIT: Horizons gives me a list ...
• 21
1 vote
97 views

Calculating local solar time with python ephem library

I was learning to calculate local solar time with ephem. I must admit, unit conversion between radians, hours and days, which are all represented by a float in the ...
• 111
1 vote
203 views

J2000 conversion to Position of date

Having spent an inordinate amount of time comparing the LBR values of Meeus (Astronomical Algorithms 1998) vs. ELP82B (Chapront's ELP82b Fortran Program) I have figured out the data set I'm using is ...
• 182
1 vote
34 views

Neptune time of perihelion/ephemeris dates

Is there a data online for the time of perihelion of Neptune between 2000AD and 3000AD? I need values in Julian Date (JD). I tried using HORIZONS Web interface, but it won't generate ephemeris for ...
• 193
1 vote