289P/Blanpain was discovered in 1819, its absolute magnitude was estimated as . It was subsequently lost and was only rediscovered in 2003. At that time, its absolute magnitude had decreased to , and it was realised that the 1819 apparition coincided with an outburst. 289P/Blanpain reached naked eye brightness (5–8 mag) in 1819, even though it is the comet with the smallest nucleus that has ever been physically characterised, and usually doesn't become brighter than 18 mag. For some comets that have been observed at heliocentric distances large enough to distinguish between light reflected from the coma, and light from the nucleus itself, an absolute magnitude analogous to that used for asteroids has been calculated, allowing to estimate the sizes of their nuclei. Meteors For a meteor, the standard distance for measurement of magnitudes is at an altitude of at the observer's zenith. See also Araucaria Project Hertzsprung–Russell diagram – relates absolute magnitude or luminosity versus spectral color or surface temperature. Jansky radio astronomer's preferred unit – linear in power/unit area List of most luminous stars Photographic magnitude Surface brightness – the magnitude for extended objects Zero point (photometry) – the typical calibration point for star flux References External links Reference zero-magnitude fluxes International Astronomical Union Absolute Magnitude of a Star calculator The Magnitude system About stellar magnitudes Obtain the magnitude of any star – SIMBAD Converting magnitude of minor planets to diameter Another table for converting asteroid magnitude to estimated diameter Observational astronomy