Your Sky Help:
Asteroid and Comet Tracking

You can plot the orbit and current position of an asteroid (minor planet) or comet by pasting its orbital elements into the text box provided for that purpose. The orbital elements, which permit calculation of the position of the object for a period of time surrounding the Epoch for which they are computed, are entered in the form currently published in the International Astronomical Union (IAU) and Minor Planet Electronic Circulars. Further information on these electronic publications, including subscription information, is given at the bottom of this page.


The first line in the text box is the name or provisional designation of the object, and the lines that follow are the orbital elements published in the Circular concerning it. If your system supports cut-and-paste, you can copy the elements directly from the E-mail Circular and paste them into the elements box.

For example, here are the elements published in MPEC 1995-C12 of February 6th, 1995 announcing the discovery of “1995 CR”, a new extremely rare “Aten-type” asteroid which orbits the Sun in less time than the Earth. 1995 CR, discovered on February 3, 1995 by R. Jedicke with the 0.9 metre Spacewatch telescope at Steward Observatory on Kitt Peak, crosses the orbits of all four inner planets. Press the “Update” button below the elements to plot this asteroid's position at the time of its discovery.

Orbital elements for asteroid or comet:

On February 22, 1995, 1995 CR passed within 0.05 astronomical units of the Earth, about 7.5 million kilometers: about 20 times the distance of the Moon. Note that we checked the “Echo elements” box above. This causes Your Sky to show the elements it obtained from the text box immediately below the box, explaining what each value means. Press “Update” again, then scroll down to see the echoed elements, if you're interested.

Recovered Asteroids and Revised Elements

Elements for recovered asteroids (those re-observed after their original discovery at a subsequent favourable apparition) and revised elements based upon refinement of an orbit by subsequent observations are published in a slightly different form, with an “Id.” line between the object's name and the epoch of the elements. Your Sky accepts this form as a well.

Here are revised elements for “1994 ES2”, a transneptunian object which orbits entirely outside the orbits of Neptune and Pluto with an orbital period of more than 311 years. These revised elements were issued in MPEC 1995-E04 of March 1, 1995 which arrived as I was writing the paragraphs above.

I've pasted the elements into the box below; press the “Update” below it to see the path of this far-flung wanderer through the darkness. I've set the time and date to the time of the most recent observation cited in the Circular, and the observing site to the latitude and longitude of Mauna Kea, Hawaii, in the United States, where the 2.2 metre University of Hawaii reflector was used to spot this 24th magnitude object.

Consulting the last line of the ephemeris, we note that at the time of the observation, 1994 ES2 shone (if I may dare to speak of a 24th magnitude object shining!) at an altitude of more than 72░ degrees in the pellucid skies with which Mauna Kea is blessed.


Orbital elements for newly discovered and recovered comets are reported in the IAU Circulars. The format in which the elements are given depends upon whether the comet is periodic (has a closed orbit around the sun) or parabolic (a comet which appears from deep space and leaves the solar system for good after its turn around the Sun, or has such a long period that its trajectory isn't measurably different from parabolic).

Periodic Comets

Elements for periodic comets are (usually) published in the following form, this example taken from IAU Circular No. 6037 of July 25, 1994, reporting the first reliable orbit determination for comet McNaught-Hartley (1994n), discovered on July 6, 1994 by M. Hartley with the 1.2 metre UK Schmidt telescope at Siding Spring, Australia.

Click the “Update” button above to see this comet from the viewpoint of the telescope which discovered it.

While the IAU Circulars publish orbital elements for periodic comets in the form given above, the Minor Planet Electronic Circulars report elements of comets in the same form they use for asteroids, except the “M” entry for mean anomaly is replaced by a “T” entry giving perihelion date. MPEC 1995-C11, issued on February 3, 1995 reported the following elements for periodic comet P/1989 T2 (Helin-Roman-Alu 1) as follows:

Your Sky detects these “stealth periodic comets” and handles them correctly, as a click on the “Update” button above will demonstrate.

Parabolic Comets

IAU Circular No. 6113 of December 12, 1994 reported the following improved orbital elements for Comet Machholz (1994r):

Click the button to see this comet as it appeared in late 1994 while making its hairpin turn around the sun, before being “last seen heading southbound on the interstellar”.

Note that elements for parabolic comets are in essentially the same form as those for (most) periodic comets, with eccentricity omitted (since it's always 1.0), and the semimajor axis, mean motion, and period dropped since they're meaningless for a parabolic trajectory.

IAU Circulars

The IAU Circulars, published by the Central Bureau for Astronomical Telegrams, provide a means for distributing time-sensitive information to observers. The Circulars announce novŠ and supernovŠ, radio and X-ray transients, newly-discovered and recovered comets. Companion Minor Planet Electronic Circulars, published by the Minor Planet Center, report asteroid discoveries and related information. IAU Circulars used to be delivered by telegram or post, but are now distributed by electronic mail. A subscription costs US$6.00 per month, and includes E-mail delivery of Circulars as they are published, and log-in privileges to a machine with an archive of Circulars as well as asteroidal orbital elements from the Minor Planet Center. You can subscribe to the circulars by sending a check (In US$) payable to the “Central Bureau for Astronomical Telegrams” to:

Central Bureau for Astronomical Telegrams
Mail Stop 18
Smithsonian Astrophysical Observatory
60 Garden Street
Cambridge, MA 02138

Fax: ++1 617 495 7231

For more information, contact the above address.

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