Questions tagged [ephemeris]
Questions about the predicted positions of an object in space, like another planet, comet, or asteroid.
83
questions
0
votes
1
answer
74
views
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 ...
5
votes
1
answer
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 ...
2
votes
0
answers
84
views
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 ...
3
votes
1
answer
232
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 ...
1
vote
1
answer
64
views
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
1
answer
84
views
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 ...
1
vote
0
answers
40
views
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 ...
0
votes
1
answer
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 ...
19
votes
1
answer
10k
views
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 ...
2
votes
1
answer
72
views
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 ...
4
votes
1
answer
215
views
CSPICE vs JPL Horizons discrepancy in AZ/EL
This CSPICE spkcpo_c routine example outputs:
...
1
vote
1
answer
97
views
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 ...
4
votes
1
answer
123
views
Different results for the same JPL Horizons query
On JPL Horizons website, I'm using the following query to get vector state for Earth:
...
16
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 ...
3
votes
1
answer
167
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 ...
5
votes
0
answers
101
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 ...
5
votes
1
answer
270
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$$\ddot{\mathbf{r}}_{i}=\sum_{j=1,j\neq i}^...
5
votes
1
answer
409
views
Orbital modelling, three bodies, leapfrog numerical integration
Apologies for the length of this question.
I'm modelling the motion of a single planet around the Sun using the equations:
$$dv_{x_{i}}/dt=a(t)=-GM_{SUN}x_{i}/r^{3},$$
where $x_{1}=x$, $x_{2}=y$ and $...
2
votes
1
answer
126
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 $\left(x,y,z\right)$ ...
1
vote
1
answer
101
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 ...
2
votes
0
answers
225
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 ...
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 ...
2
votes
0
answers
640
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 ...
9
votes
1
answer
599
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, ...
3
votes
2
answers
481
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 ...
7
votes
1
answer
309
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 ...
4
votes
1
answer
300
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 ...
5
votes
1
answer
195
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 ...
3
votes
3
answers
230
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 ...
3
votes
1
answer
116
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 ...
4
votes
1
answer
186
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 ...
1
vote
0
answers
586
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 ...
4
votes
0
answers
243
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 ...
4
votes
2
answers
176
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 ...
1
vote
1
answer
129
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 ...
3
votes
1
answer
239
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
2
votes
0
answers
114
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 ...
2
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 ...
2
votes
3
answers
133
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 ...
21
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 ...
7
votes
4
answers
331
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 ...
1
vote
0
answers
47
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 ...
6
votes
0
answers
97
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 ...
0
votes
1
answer
191
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 ...
6
votes
0
answers
172
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 ...
5
votes
4
answers
454
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 ...
3
votes
1
answer
275
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
1
answer
139
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 ...
4
votes
2
answers
443
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 ...
3
votes
1
answer
406
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 ...