Precise ephemeris directly from the JPL HORIZONS System

All downloaded files from the JPL and MPC contain the orbital elements of comets and asteroids. Coelix uses the orbital elements (perihelion distance, inclination, semi-major-axis, etc..) to calculate the ephemeris and positions of comets and asteroids. These calculations give very accurate results in most cases.

However, the downloaded orbital elements are osculatory, that is to say, they change over time and are only valid for a limited period. In addition, Coelix calculations do not include the effects of gravitational perturbations from objects other than the Sun, such as planets and large asteroids. So there may be a discrepancy in some cases, especially when a comet or asteroid passes close enough to Earth.

Since the 2.094 version, Coelix includes dozens of comets and asteroids whose ephemeris are directly calculated by the JPL Horizons system. These ephemeris give very accurate positions that reflect the gravitational perturbations. These ephemeris are calculated for six months before and six months after the date of perihelion passage for comets or opposition for asteroids. Outside these dates, Coelix calculates the ephemeris from the orbital elements only.

When you display the table of ephemeris of a comet or an asteroid in Coelix, an asterisk (*) in column (H) indicates that the ephemeris of this line comes from the JPL Horizons system. When you display the path of a comet or an asteroid, the position on the map reflects the ephemeris JPL Horizons system.

Normally, you do not need to separately download these ephemeris since they are part of the regular updates of Coelix. However, we explain below how to add comets or asteroids that are not in the following lists.

The folders of comets and asteroids for the current version
How to add comets and asteroids from the JPL HORIZONS System
It is possible that you need to get very precise ephemeris of a comet or asteroid that is not in the folders above. Then there are two choices. You can download it directly from the JPL HORIZONS website or you can ask us by sending an email to the address given in the "Contact" page of this site.

The comet or asteroid must also be already accessible by Coelix (in the lists of MPC comets, JPL asteroids, or favorites).

If it is not, you can update the lists here.

Here are the steps to follow if you choose to download the ephemeris:

1 - Go to the website of the JPL HORIZONS System:
You get a form to enter the settings of the object you want to view the ephemeris:
2 - Change the settings to get the desired object ephemeris in the format required by Coelix;

Ephemeris Type: OBSERVER (leave unchanged).

Body Target: choose the desired comet or asteroid.

Observing location: leave Geocentric [500]. This is Coelix that will take care of calculating topocentric coordinates.

Time Span
   Start: six months before the opposition of an asteroid or a comet's perihelion;
   Stop: six months after the opposition of an asteroid or a comet's perihelion;
   Step: Choose a step of one day.
   (Note: you can choose different values in the case of a rapid near-Earth asteroid such as 2012 DA14, eg a step of one hour, and ten days before and after the opposition for Start and Stop).

Table Settings:
   Keep only choices # 1 and # 9. Deselect all others.
   Date/Time Format: select BOTH;
   Angles Format, choose decimal degrees.

Display Output: select Plain text.

You get a form that looks like this:
3 - Click on the "Generate Ephemeris" button to get the ephemeris table.

4 - In the resulting table, only select all of the text that is between the markers $$SOE. Do not include these markers.

5 - Copy the selected text to the Windows Notepad. Make sure that you get a well aligned document that looks like the following example for the asteroid Juno:
6 - Save the Notepad text file in the Coelix asterhp folder (for an asteroid) or comethp folder (for a comet), according to the following rules of nomenclature:

For a numbered asteroid, the file name must begin with a_ followed by the seven digits of the asteroid number, for example 0000003 for Juno, which would give a_0000003.txt for Juno.

For an unnumbered asteroid, the file name must also start with a_ followed by the year and the nomenclature of the asteroid in uppercase, with spaces replaced by underlined bars, which would give a_2012_DA14.txt for asteroid 2012

For a comet, the file name is the name of the comet in which separators and spaces (but not dashes) are replaced by underlined bars, which would give for example 46P_WIRTANNEN.txt, C_2012_S1_ISON.txt,
41P_TUTTLE-GIACOBINI-KRESAKetc.. Use only capital letters.

7 - Test the operation of your new file in Coelix by displaying a table of ephemeris of the comet or asteroid. Also check that there is an asterisk (*) in the column (H) of the table for the dates within the limits of the ephemeris calculated by the JPL Horizons system and that there are no asterisks outside these dates. It is normal that three days are missing at the beginning and the end of the selected time limits to allow interpolation by Coelix.

In case of problem, you can check the contents of the files that are already in the folders asterhp and comethp of Coelix. You can also ask us to email you the file of the desired object.

The current version of Coelix Apex contains Horizons system ephemeris for the asteroids brighter than magnitude 10.5 to the opposition (limit magnitude of 9.5 for Coelix Lite), whose opposition occurs until six months after the release date of the version.

The range of Horizons ephemeris is six months before the opposition of the asteroid until six months after.

You can find in the folder comethp, the comets files whose ephemeris are from the HORIZONS system.
Similarly for asteroids, the asterhp folder contains asteroids files whose ephemeris are from the HORIZONS system. The file names contain the asteroids numbers, such as a_0000003.txt for Juno, the asteroid number 3.