Skip to content

MPC Minor Planet & Comet Ephemeris Service

The Minor Planet Center (MPC) provides an online service that allows users to accurately generate ephemerides for comets and minor planets. This is my page with notes on how to use the service in planning an observing session.

I am mainly interested in getting the object’s RA/Dec coordinates and sky motion in arcseconds per hour. Usually in ten minute intervals over a six hour period.

Using the Service

First, open the MPC Ephemeris Service form at: MPC Ephemeris Service

Second, enter the requested information into the form’s fields. Help for some of the fields follows below (additonal help is available here:  MPC pdf documentation ).

Date and Time

Example: 2021-12-13  0400  (December 13, 2021 starting at 04:00 UT)

Other acceptable forms for entering dates are:
2003 06 10 (0h UT on 2003 June 10)
1965 12 10.5 (12h UT on 1965 Dec. 10)
1903 09 10 12 (12h UT on 1903 Sept. 10)
2003 July 10 (0h UT on 2003 July 10)
2023 June 10.75 (18h UT on 2023 June 10)
1998 Jan. 10 121314 (12h13m14s UT on 1998 Jan. 10)
1923-06-23 (0h UT on 1923 June 23)
1930-Feb-18 19 (19h UT on 1930 Feb. 18)
1997/03/31 (0h UT on 1997 Mar. 31)

Object Designation

Examples (case sensitive): 67P, 67P/Churyumov-Gerasimenko, C/2021 A1 (for C/2021 A1 Leonard), 4P, 4P/ Faye

Other valid forms of designation input are:
(3202) Numbered minor planet (3202)
14829 Numbered minor planet (14829)
1997 XF11 Unnumbered minor planet 1997 XF11
1P Comet 1P/Halley
C/2003 A2 Comet C/2003 A2 (Gleason)
P/2003 CP7 Comet P/2003 CP7 (LINEAR-NEAT)
In addition, designations may also be entered in the following packed formats:
00233 Numbered minor planet (233)
K03A07A Unnumbered minor planet 2003 AA7
PK03C07P Comet P/2003 CP7 (LINEAR-NEAT)
0039P Comet 39P/Oterma

For comets, it is not necessary to know whether a particular comet’s prefix is C/ or P/. As long as you include one of these prefixes, the correct comet will be located

or Object Name
Both minor planets and comets may be searched for by name. The entered names must be complete (no partial names) but are not case sensitive: e.g., entering “GrAfF” will locate numbered minor planet (3202) Graff. Comet names must be prefaced by either C/ or P/ (it does not matter which). If a comet name is not unique, the first match will be returned.

Examples of valid entry are:
• Encke (9134) Encke
• Africa (1193) Africa
• Africano (6391) Africano
• P/Encke 2P/Encke
• C/Encke 2P/Encke
• C/Gleason C/2003 A2 (Gleason)

Ephemeris start date
Enter the desired start date in one of the formats detailed above. If left blank,the start date defaults to the current date and time (possibly modified by the desired interval).

Number of dates to output
Enter the number of ephemeris dates desired. If left blank, the number defaults to either 21 (if the ephemeris unit is daily), 49 (if hourly), 121 (if minutely) or 301 (if secondly). The maximum allowable number of ephemeris dates is 1441 (for all types of ephemeris unit).

Ephemeris interval
Enter the dimensionless ephemeris interval. For example, if the desired interval is 6 hours,enter ‘6’. If left blank, the number defaults to 1.

Ephemeris units
Select the desired ephemeris units (days, hours, minutes or seconds) using the radio icons.

Longitude, Latitude, Altitude

Example: Longitude: -97.5169 Latitude: 35.6608 Altitude (m): 340

Motion and Direction

Select the radio buttons for Separate R.A. and DecL. coordinate motions and “/hr. PhD2 needs this information in these units for its comet (and asteroid) tracking tool.

Total motion and direction is useful for estimating maximum exposure length before smearing of the image occurs.