Questions tagged [ephemeris]

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

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Inconsistency between Horizons data retrieved via Astroquery and Horizons web interface

I am attempting to obtain the x, y, z coordinates of the Sun-asteroid vector using Horizons. The code I wrote is: ...
Milagros Colazo's user avatar
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43 views

How to find the Moon's node longitude crossing

Yes, I asked this in the past but I got sidetracked and did other things. Now my question is, can one find the exact time when "north node" reaches a certain longitude? I am looking for 15....
dimitri33's user avatar
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What are ephemerides? (SPICE software)

I want to use the SPICE software, but there is something than I don't understand: The purpose of the SPK---which stands for S(pacecraft) and P(lanet) Kernel---file is to allow ephemerides for any ...
VansFannel's user avatar
5 votes
2 answers
577 views

How to calculate the true distance of the sun and the earth using skyfield?

I'm trying to calculate the true distance between the sun and the Earth using skyfield. To estimate the distance at a time instance I use the barycentric coordinates of the sun and earth using the ...
Klaus Rohe's user avatar
4 votes
2 answers
135 views

Resolving variance between Skyfield-generated sun vectors and test data when both use same ephemeris

I have two functions that get TEME and GCRS Earth-Sun position vectors using Skyfield: earth_sun_vectors.py ...
Michael Bonnet's user avatar
2 votes
1 answer
85 views

Chiron ephimeris calculations

I am able to find the current location for 95P/Chiron using swisseph with a simple code but i am interested into trying to calculate longitude crossings including retro etc .. but at first i only ...
dimitri33's user avatar
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1 answer
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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 ...
codingEnthu's user avatar
5 votes
1 answer
117 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 ...
BillR's user avatar
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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 ...
Joe Horwath's user avatar
3 votes
1 answer
292 views

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 ...
Ath Genube's user avatar
1 vote
1 answer
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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 ...
warherolion's user avatar
2 votes
1 answer
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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 ...
uhoh's user avatar
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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 ...
An ominous cow word's user avatar
0 votes
1 answer
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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 ...
Smarty's user avatar
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20 votes
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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 ...
Haywire's user avatar
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1 answer
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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 ...
chris trejo's user avatar
4 votes
1 answer
232 views

CSPICE vs JPL Horizons discrepancy in AZ/EL

This CSPICE spkcpo_c routine example outputs: ...
phil5's user avatar
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1 vote
1 answer
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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 ...
Radium's user avatar
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4 votes
1 answer
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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: ...
Claudiu's user avatar
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17 votes
2 answers
3k views

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 ...
Peter's user avatar
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3 votes
1 answer
188 views

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 ...
Michael Cole's user avatar
5 votes
0 answers
107 views

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 ...
zero0cool's user avatar
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5 votes
1 answer
286 views

Question about Cowell's method

According to Wikipedia: “ ... for $n$ mutually interacting bodies, Newtonian forces on body $i$ from the other bodies $j$ are” given by the summation equation$$\ddot{\mathbf{r}}_{i}=\sum_{j=1,j\neq i}^...
Peter's user avatar
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5 votes
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Orbital modelling, three bodies, leapfrog numerical integration

Apologies for the length of this question. I'm modelling the motion of a single planet around the Sun using the equations: $$dv_{x_{i}}/dt=a(t)=-GM_{SUN}x_{i}/r^{3},$$ where $x_{1}=x$, $x_{2}=y$ and $...
Peter's user avatar
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2 votes
1 answer
138 views

Orbital modelling - best choice for initial JPL Horizons data?

I'm modelling planetary orbits using a spreadsheet and Feynman's numerical method given here. I have put together a spreadsheet (10,000 rows) to model Mars' orbit in three $\left(x,y,z\right)$ ...
Peter's user avatar
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1 vote
1 answer
102 views

How can I retro search for time periods with specific planetary alignments?

Let's say we have a planetary ecliptic longitudes of an unknown period. What program or software or procedure can one use to arrive at the range of time periods where the planets were in those ...
Profile name's user avatar
2 votes
0 answers
265 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 ...
uhoh's user avatar
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10 votes
2 answers
2k views

JPL Horizons - "highly accurate measurements of planetary positions" - how do they do it?

According to JPL Horizons, with regard to their planetary position calculations, ... we integrate the equations of motion in Cartesian coordinates ($x,y,z$), and we adjust the initial conditions in ...
Peter's user avatar
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2 votes
0 answers
763 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 ...
Sati's user avatar
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9 votes
1 answer
603 views

What unit of year in JPL Small-Body Database Lookup?

I'm new to astronomy and therefore probably missing the obvious here, but what type of year (tropical, sidereal?) is used for the orbital periods in the JPL Small-Body Database Lookup? For example, ...
Peter's user avatar
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3 votes
2 answers
630 views

Calculation of Terrestrial and Universal time scale difference, ΔT

$\Delta$T is defined as the 'measure of the cumulative effect of the departure of the Earth's rotation period from the fixed-length day of atomic time'. I tried to calculate $\Delta$T corresponding to ...
Smarty's user avatar
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7 votes
1 answer
322 views

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 ...
ordptt's user avatar
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4 votes
1 answer
375 views

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 ...
mark03's user avatar
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5 votes
1 answer
221 views

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 ...
Rafa's user avatar
  • 351
3 votes
3 answers
264 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 ...
Rafa's user avatar
  • 351
3 votes
1 answer
127 views

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 ...
uhoh's user avatar
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4 votes
1 answer
216 views

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 ...
Rafa's user avatar
  • 351
1 vote
0 answers
626 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 ...
Danny F's user avatar
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4 votes
0 answers
248 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 ...
Peter's user avatar
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4 votes
2 answers
192 views

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 ...
mysterium's user avatar
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1 vote
1 answer
137 views

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 ...
huab's user avatar
  • 143
3 votes
1 answer
256 views

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
Elena Greg's user avatar
2 votes
0 answers
116 views

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 ...
Orion's user avatar
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4 votes
2 answers
1k views

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 ...
B--rian's user avatar
  • 5,616
2 votes
3 answers
146 views

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 ...
jumpjack's user avatar
  • 569
20 votes
3 answers
5k views

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 ...
mr_tuna's user avatar
  • 303
7 votes
4 answers
341 views

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 ...
Pierre Paquette's user avatar
1 vote
0 answers
52 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 ...
posfan12's user avatar
  • 193
6 votes
0 answers
100 views

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 ...
Jack Schmidt's user avatar
1 vote
1 answer
209 views

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 ...
user177107's user avatar
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