# Questions tagged [ephemeris]

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

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### Where can I get historical data of tropical longitude of Delta Cancri

I need historical data of tropical longitude of Delta Cancri. Where can I get it. As of now it is approximately 128 Deg from Vernal Equinox. Where can I get it's historical data, say from 5000 BC to ...
109 views

### Formula to Determine When a Target Reaches a Specific Altitude

I'm trying to develop an Excel macro to compute when a target will rise above a specified altitude given the date and location. I can get the correct answer with Stellarium and using a Python program ...
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### What are the orbital periods Jupiter, Saturn and earth?

What are the highest accuracy (and hence precision) orbital periods of Jupiter, Saturn and earth in units of days. Note have Allen’s Astronomical Quant(Cox1991)/ Wolfram-α / Wikipedia / 3ea. don’t ...
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### How to test accuracy of DE441?

I want to write about processing DE441 data for Moon and Sun and include a section about the validation and accuracy testing of the algorithm. Is there a website where I can retrieve documentation for ...
1 vote
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### Mismatch between Nasa Horizons Alt & Az data and theskylive and other star maps

I am trying to use NASA's Horizons systems to create a tracker for planets but I am running into a problem related to the returned ephemeris data, particularly with the altitude and azimuth. When ...
1 vote
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### What is the difference between SPICE kernels and JPL Development Ephemerides? Is a DE just a bunch of kernels on a string?

My imposter syndrome is acting up again after I posted several comments under: What is the mathematics needed for understanding DE440 and translating it into xyz coordinates? Now I feel like I don't ...
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1 vote
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### How can I find or calculate ephemeris data for the planets in an extrasolar system, specifically Trappist-1?

The ultimate, perfect answer would be a link to someone's ephemeris file in SPICE kernel format. That's not a realistic hope. Googling and gnawing, I've found orbital periods, eccentricities, and ...
130 views

### Following Meeus's Astronomical Algorithms for the Calculation of JD

For the Calculation of Julian Day (JD), I followed Chapter 7 of Meeus's Astronomical Algorithms. I could get the numbers mentioned in Example 7.a and 7.b. On the basis of these methodology, proceeded ...
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### JPL Horizons sending too many emails

I submitted a job that, I think, should have returned 100 emails from JPL Horizons. I now have over 6000 emails and they are coming in at about four a minute. Anyone else had this problem? Anyone know ...
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### Finding the Phase of an Exoplanet using the ephemeries

So I'm currently researching Star-planet Interactions for HD 156279, I'm taking the flux of the Ca II H&K lines and trying to plot them against the phase of the planet, looking for evidence of ...
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### CSPICE vs JPL Horizons discrepancy in AZ/EL

This CSPICE spkcpo_c routine example outputs: ...
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1 vote
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### How to get the name of an asteroid if I have it's RA - dec position at a particular time?

I have the RA - Dec position of a potential asteroid and the time at which it was taken. Is it possible to use this information to get more information about this asteroid, like its name, orbital ...
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### Different results for the same JPL Horizons query

On JPL Horizons website, I'm using the following query to get vector state for Earth: ...
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### How do planetarium apps and software calculate positions?

In the most general terms (I'm not asking for the actual calculations), how do popular planetarium apps and software calculate the positions of celestial objects? Planets, for example. Do they use ...
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### How to get JPL Ephemeris data to work in n-body simulation or why is Mercury flying to Jupiter

I wanted to make a n-body simulation for an art project. I used this n-body algorithm, which includes a stable system for the Sun + gas giants, but no inner planets. I wanted to simulate inner planets ...
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### Beginners question about time scales

I'm using https://github.com/Bill-Gray/jpl_eph for a personal project to read JPL DE files, namely DE430 and the more recent DE440. This generally works great and when tested against a reference ...
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### Earth-Moon Barycenter Perihelion

I am trying to implement an algorithm I created to get the sun rise, transit and set accurately, but in order to do that I need to get the Earth-Moon barycenter (EMB) perihelion, and not the Earth ...
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### How can I calculate my position (lat/lon) given a sequence of solar-elevation measurements at known times?

The "forward" problem (given time and lat/lon, find solar position angles) is well documented, e.g. here. I am trying to figure out the "inverse" problem: given time and [a ...
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### Discrepancy in Horizons planet ephemerides for equivalent times in TT and UTC in dates during 1969

I have recently been experimenting with JPL Horizons planet ephemerides web App, and found a puzzling discrepancy. Horizons allows to specify the time at which the planet ephemerides should be ...
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### 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 ...
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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 ...
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### Discrepancy between my calculated planet JPL ephemerides and those by Horizons online app

I'm currently using JPL DE440 ephemerides. Following the documentation here, verified with the header file (specially the records in GROUP 1050) for the DE440 ephemerides (file header.440 available ...
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1 vote
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### 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 ...
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### 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 ...
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### Uncertainities of orbital elements queried from JPL Horizons

I'm trying to retrieve the orbital elements' uncertainities for asteroids queried from NASA JPL Horizons. However I'm not able to find them in the query fields returned in python. Nor am I able to ...
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1 vote
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### What are the aspects does the moon differs between cities located on the same latitude?

What are the aspects does the moon (astronomical position and other astronomical aspects) differs between cities located in the same latitude? - For example: Seattle, Munich, Vienna, and Ulaanbaator ...
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### Linear ephemeris

What is the T in the formula for the linear ephemeris T_max = T + P*E, please? P stands for the period; E, for ephemeris. How to determine T? I have T_max and P. Or is it a referent epoch? Many thanks
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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 ...
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### Accuracy of calculating the vernal equinox?

Calculating the exact time of the vernal equinox is essential for many ephemeris calculations. NASA Goddard Institute for Space Studies uses (at least for some purposes) the following, rather short ...
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### How to determine when Sun/Moon is aligned to two location on Earth's surface?

I would like to make a photo to Moon/Sun when it is very low on horizon, so if I make the shot far away from an object on Earth surface, it appears as big as the Sun. But how can I calculate the right ...
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### Why won't the Sun set for days at N66.2 which is below the arctic circle?

Correct me if I am wrong, but if we count sunsets by the center of the Sun apparently crossing the horizon then the Sun is supposed to set every day at latitudes under the arctic circle. (Yes if you ...
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### Apsides Calculation

I’m trying to calculate the precise moment of Earth’s apsides (perihelion and aphelion). The only formulas I find are in Astronomical Algorithms by Jean Meeus (1998). However, they give erroneous ...
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1 vote
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### 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 ...
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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 ...
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### Is there any ephemeris generator that gives you accurate distances between Earth and other bodies?

I've tried JPL's HORIZONS ephemeris generator and while it gives accurate celestial coordinates for an object it doesn't give the geocentric distance. JPL's Solar System Simulator gives the distance ...
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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 ...
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### Instantaneous gravity in equation of motion for ephemerides calculation

The equation of motion used for the calculation of orbits of solar system objects (Eq(27) in https://ipnpr.jpl.nasa.gov/progress_report/42-196/196C.pdf ) is formulated in terms of instantaneous ...
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### How to calculate the point on the globe with maximum magnitude with given Besselian elements and given time for a partial solar eclipse?

I am currently working on improvement of an Android app that calculates solar eclipses. For many days now I have not been able to solve a mathematical problem concerning solar eclipses, so I decided ...
1 vote
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### Can I calculate the apparent position of comet NEOWISE C/2020 F3 from a topographic position with Skyfield?

I'd like to get .altaz(next_several_weeks) of this comet from Skyfield and .separation_from() other planets. It reads the JPL ...
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