International Comet Quarterly

Further Helpful Hints Concerning Cometary Photometry

• Visual photometry of comets
  • Note that there are a few different acceptable methods for properly obtaining a total visual magnitude estimate of a comet.
  • Ideally, observers should strive to make total visual (or CCD) magnitude estimates of comets once every possible night (and only once per night, particular in the case of visual observations, unless the comet is observable all night long and very close to the earth, when a real brightness change may be noticeable in several hours' time).
  • Observers should always use comparison stars with visual or V magnitudes from acceptable professional catalogues, and a minimum of 2-3 stars should be used for each estimate that are within 0.5 magnitude of the comet's brightness; use of deep-sky objects (galaxies, nebulae) are NOT acceptable for deriving comet brightnesses. Observers using V comparison-star magnitudes should be careful to avoid red stars (that is, those with B-V > +0.7 or so, especially K, M, and later-type stars, because they will appear 0.1-0.4 mag fainter to the human eye than their V values suggest).
  • Observers of comets making total visual magnitude estimates should always use the smallest instrument needed to easily see the comet, due to large instrumental effects that can again cause values to be too faint.
  • When comets are less than 20° or 25° from the horizon, the observer should usually correct for atmospheric extinction.

• CCD photometry of comets
  • Primer on CCD photometry of comets, from ICQ's 1997 Guide to Observing Comets

• All photometry of comets: The description of the ICQ format for contributing photometry of comets explains the sorts of data that are important to astronomers for archiving such observations. Please read this carefully, noting that much more information is required of CCD photometrists (bottom of webpage).

Recent comet magnitude estimates