User:Tomruen/H-G magnitude system


 * 1) Commission 20 recommends that the minor planet magnitude system put forward by the ad hoc Committee on Magnitude Ephemerides be adopted for use in publications that conform with the policies of the Commission. A formula for the prediction of the apparent magnitude of a minor planet is
 * 5 log r + H - 2.5 log [(1 - G) o + G o ],
 * where r and are, respectively, the heliocentric and geocentric distances (in AU), H is the absolute magnitude (in the V band unless otherwise specified) at solar phase angle = 0, G is termed the slope parameter, and o and o are two phase functions approximated by
 * o = exp {-A [tan(&alpha;/2)]B }; i = 1, 2
 * A = 3.33, A = 1.87, B = 0.63, B = 1.22.
 * OR H =H(α) + 2.5log[(1−G)φ1(α) + G φ2(α)], where:
 * φi(α) = exp{−Ai(tan(α/2))Bi}, i = 1 or 2, A1 = 3.33, A2 = 1.87, B1 = 0.63 and B2 = 1.22 and α is the phase angle in degrees.
 * 1) It is recommended that, for numbered minor planets, values of H and G be published annually in the Efemeridy Malykh Planet, that files of photometric data be maintained and frequently updated, and that the files files be overseen and approved for publication by a standing committee.
 * 2) If G cannot be satisfactorily determined, and in the absence of albedo or taxonomic class, it is sufficient to adopt the value G = 0.25. If further sophistication is desired, it is appropriate to adopt instead G = 0.15 if the minor planet appears (even in the absence of available proper elements) to belong to the Nysa family or to have semimajor axis a > 2.50 AU (unless it is an Apollo object), or G = 0.40 if it appears to belong to Williams family 190.

Note: It is anticipated that the new magnitude formula will become effective with respect to orbits and ephemerides appearing in the MPCs for 1986 Jan. 26 and in the EMP for 1988. USERS SHOULD NOTE IN PARTICULAR THAT VISUAL (V) RATHER THAN PHOTOGRAPHIC (B) MAGNITUDES WILL BE UTILIZED IN EPHEMERIDES IN THE FUTURE. However, observations made in the B system are quite acceptable. The principal advantage of the new formula is that the opposition effect is handled in a more logical way and thus that there is a more straightforward relationship among the absolute magnitude, albedo (which can be associated with the slope parameter G) and diameter. The combined effect of this and the conversion from B to V is that H B(1,0) - 1.0. The new formula is reliable to at least = 120. A more accurate version of the formula and extensive additional information are contained in the paper "A Two-Parameter Magnitude System for Asteroids", by E. Bowell, A. Harris and K. Lumme (available in preprint form from the first author). M. P. C. 10 194 1985 DEC. 27 Values of H and G for the numbered minor planets are being prepared by E. Tedesco, Jet Propulsion Laboratory, and it is hoped that the first version of these values will be published in the MPCs in the near future. The standing committee consists of E. Bowell, Y. Kozai and B. G. Marsden.