IAU Central Bureau for Astronomical Telegrams

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So You Think You've Discovered A Comet...


"Discovering" a comet means different things depending on whether one is a very experienced observer or is a beginning observer. For every real new comet discovery, the Central Bureau for Astronomical Telegrams (CBAT) gets perhaps five reports of "discoveries" that do not pan out. And in most of these unconfirmed or erroneous discovery reports, the observers declare "NEW COMET" or "COMET DISCOVERY", even though they have only seen the possible object once (with no detectable motion), or even though they only have a single photograph on one night with a suspicious-looking object.

If you think that you might have come across a new comet, there is a check-list that you should go through before proceeding further:

  1. Can you be absolutely sure that the image is real? This is a very common problem, with both visual and photographic observers finding "ghost images" caused by nearby bright objects (stars, planets, etc.) and then reporting them as possible comets. Beware that even very experienced professional astronomers are sometimes fooled by ghost images!
  2. Is there motion? If so, determine how much the object moves in a measured amount of time. If there is no definitely-detectable motion, be very skeptical. Be sure that there are no close asterisms (a big problem with visual observing) or no galaxies at the position in question. Many observers reporting "discoveries" do not have access to good atlases or catalogues and do not notice that their "comet" is in fact an entity far beyond our own solar system! Do not rely solely on Atlas 2000.0 or the Skalnate Pleso Atlas, for example; photographic atlases are far preferable to drawn or computer-generated atlases (both of which often have glaring omissions).
  3. As accurate a position as you can measure will be needed if you still think that you have a comet. A position accurate to at least 1' in Declination and 0.1 minute of time in Right Ascension is not too difficult using most available atlases with grid overlays, and such accuracy is often very necessary to prevent observers from wasting much time in searching for an object.
    • The equinox should also be stated (2000.0 or 1950.0 being the most-widely used).
    Just as important as the position is recording the time of observation, which should be reported in Universal Time (not local time), preferably in decimals of a day (not hours/minutes), to 0.001 day or better. If you have a photograph or especially a CCD, you really should provide accurate positions from all of your images, to 0.01 second of time for the right ascension (R.A., or Greek-letter alpha) and to 0".1 for the declination (Decl., or Greek-letter delta).
  4. A reasonable description is also useful, including an estimation of the object's total magnitude and a note concerning its size, amount of diffuseness, possible tail information, and degree of central condensation.
  5. When reporting information, give your full name, mailing address and a telephone number where you can be reached. Also give information such as your observing location and instrument used for detecting the object (including aperture, type of telescope, and, in the case of photography, what kind of film and exposure times are involved). Specify what sources you have checked to rule out alternative explanations (including known comets and deep-sky objects).
Always note that a CONFIRMATION observation on a second night is always recommended before reporting the object to the professional community; at the least, observe the comet with different instruments if possible over as much time on a single night as possible, and try obtaining multiple CCD or photographic exposures --- reporting all such observations/images available. This has always been a standard policy of the prolific comet discoverer William Bradfield of Australia (who has all 17 of "his" comets named solely for him, with no other names of other discoverers shared). Telescope time is so scarce and valuable at professional observatories that it becomes a real problem when lots of false alarms are searched for.

Check the ICQ Comet Information Website for explanations for any of the terms or concepts discussed on this page.

Now, if you're still convinced that what have found is really a comet, it would be helpful if you could check one of the several readily-available publications listing ephemerides of already-known comets. At any given time, there are usually at least 2 or 3 (often more) comets visible in the night sky which are within the visual range of an 8-inch reflector. Good sources for the positions of known comets include the Minor Planet Circulars, the annual Comet Handbook of the International Comet Quarterly, the online ephemerides of the Minor Planet Center, and the annual Handbook of the British Astronomical Association.

It is a good idea to contact a local observatory (or one or more experienced amateur astronomers) privately (not publicly) to ask for confirmation before reporting it to the CBAT. But do not post discovery information on any Internet venue (whether discussion groups or Websites), because many inexperienced people will potentially be exposed to this information --- leading to potential wild-goose chases and even perhaps eliminate the chance that a comet will be named for you (to ensure that discovery rights rest with you, if you find a comet, you must contact the Central Bureau first). The best procedure for getting information to the Bureau is via an e-mail message to the address cbatiau@eps.harvard.edu. Please note that the Bureau's TWX number was discontinued for lack of use on 1995 July 1.


Based on an article written by D. W. E. Green and published in Sky and Telescope.


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