# Questions tagged [ephemeris]

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

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• 61
250 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 ...
• 173
96 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 ...
• 33
157 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 ...
• 344
149 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 ...
• 344
73 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 ...
• 31.8k
94 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 ...
• 344
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
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
149 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 ...
• 697
1 vote
91 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 ...
• 143
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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
• 441
86 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 ...
• 21
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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 ...
• 5,304
88 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 ...
• 483
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 ...
• 313
275 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 ...
• 4,897
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
85 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 ...
• 260
126 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 ...
• 2,222
82 views

### 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
415 views

### 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 ...
• 2,318
160 views

### 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
121 views

### 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 ...
• 31.8k
347 views

### Understanding the JPL Ephemerides

I'm working on an animation that replicates our Solar System. I know this has been done before, but I'm working on something that requires me to make one myself. With that being said, I'm having a ...
• 235
266 views

### Determining moonset time from Nautical Almanac

I have recently learnt to determine moonrise and moonset times using the Nautical Almanac, as part of my maritime navigation course. I have a query regarding the determination of moonset times. I will ...
1 vote
305 views

### Implementing the VSOP-2000 Ephemeris

For a project I'm doing, I need to implement the VSOP-2000 ephemeris for the Moon. However, unlike VSOP-87, there is little to no documentation online on how to use the data. For example, here is the ...
128 views

### How accurate should sun\moon ephemeris be for calculating eclipses?

I am writing a program to simulate eclipses for about -2000 to 6000. My question is, how accurate does my ephemeris for the sun and moon have to be to get a decent accuracy for eclipses? I currently ...
1 vote
26 views

### Is it correct to say vertical conjunction?

This question is related to this one: Are we seeing a conjunction these mornings? Last Feb 27, the a reporter said that, the day before, at sunset, Venus and the Moon were in vertical conjunction. Is ...
• 489
479 views

### Precision in the measurement of the distance to the Sun

How precisely can the distance to the Sun be measured? Wikipedia says the distance to the Moon can be measured upto millimeter precision. But Wikipedia article on distance to the Sun says only about ...
98 views

### How can I calculate 27 tropical/solar year since my birthdate?

Let's say I was born on 27th November 1993 at 03:15:15 AM. Is there any way I can calculate exact 27 tropical cycle since my birthdate/birthtime. What date and what time it will be after exact 27 ...
• 113
161 views

### L2 point ephemeris (celestial mechanics)

I'm a master student and I am trying to get the L2 ephemeris for some calculations in my master's project. It was kinda hard to find a file with the L2 ephemeris, but once I found it, I tried the next ...
3k views

### 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 ...
1 vote
127 views

### How to choose between methods to resample/interpolate ephemeris state vectors? Are there recognized techniques for orbital data?

I have ephemeris data for state vectors of a satellite in a J2000.0 coordinate system. This data is already filtered and cleaned. The data sample rate ranges between 1 second and 60 seconds, and I ...
• 19
1 vote
5k views

### How to calculate the ground track of the Moon's position on the Earth's surface?

I would like to project the Moon's position on to the surface of the Earth, starting with its position expressed as Right Ascension in degrees. I know that the declination of the Moon corresponds to ...
• 113
1 vote
976 views

### How to get ephemeris data for location?

How can I obtain ephemeris data which fits to a specific location? Differently phrased: I need ephemeris data of satellites which orbited a specific location. Is there a document where I can look up ...
• 113
576 views

### Calculating right ascension for two planets and their separation using python

I am experimenting with the Python library PyEphem for astronomy, and I am trying to recreate/understand some of the basic calculations there. There is a function called separation that, given two ...
• 123
861 views

### Why is the time between equinoxes different?

The path of the Earth around the sun is described as being an ellipse, with the Sun being at one of the foci of the ellipse. Since an ellipse, by definition, is symmetrical with respect to the foci, I ...
• 815
157 views

### Predicting accurate time of local sunrise in mountainous area?

Is there any software which will tell me accurately at what moment any part of the solar disk will become from a specific point on the ground taking account of terrain. I feel like Google maps should ...
• 9,933
372 views

### Ephemeris data mismatch between Nasa Horizonz and Astro.com

I have tried to compare the Ephemeris data from Nasa's Horizons with ephemeris tables from astro.com. And they do not match. Example: Date: 22th of July 2018. Body: Mars. Time 00:00 UT Horizons: 309 ...