Brightness Changes in Periodic Comets.

Abstract

view Abstract Citations (2) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Brightness Changes in Periodic Comets. Whipple, Fred L. Abstract Secular changes ii~ the absolute magnitudes of periodic comets, averaged over each perihelion passage, have been derived from data by Vsekhsviatsky. The intrinsic brightness, at 1 a.u. from earth ai~d sun on an r-4 law, is assumed to vary as ~(1 -Xt)2, where ~ and X are constants characteristic of each comet and t is the time; t period. The relation is based upon the concept of an icy cometary nucleus that shrinks linearly with the time, where the brightness varies as surface area times rate of mass loss per unit area. By least squares the relation fits the observations within their accuracy; approximately +1 mag. The quantity ~X2 measures a physical characteristic of each cometary nucleus iiot yet correlated with other observed characteristics. Applied literally, the theory predicts that cometary nuclei disintegrate to nothing. Predicted death dates for selected periodic comets are as follows: Pons-Winnecke, 1958-1962; Tuttle, 1959; Wolf 1, 1964-1971; Kopff, 1966; Brooks 2, 1967; Faye, 1967; Whipple, 1967; Encke, 1993; and Halley, 2458. Note that Pons-Winnecke was not found in its 1957 passage, nor Tuttle in 1953. The precision with which comets actually follow this forecast will be a partial test of the degree to which cometary nuclei truly disappear. On the other hand, a few may become erratically inactive before total disintegration. The author finds no correlation between cometary magnitudes by Vsekhsviatsky and Bobrovnikoff and sunspot numbers or phase in the solar cycle. Extrapolation into the past indicates that Encke's comet should have reached second to third absolute magnitude in the first three centuries B.C. when its orbit intersected that of the earth at a small inclination (~5O) Thus there is strong hope of finding it in Chinese or Babylonian records; the associated Taurid meteor streams indicate ai~ age of some 4000 years or more. Phenomenal meteor showers should have occurred near the time of orbital intersection. Publication: The Astronomical Journal Pub Date: 1964 DOI: 10.1086/109434 Bibcode: 1964AJ.....69R.152W full text sources ADS |