On the variation of cometary coma brightness with comet-Earth distance (the Delta Effect)

Details On the variation of cometary coma brightness with comet-Earth distance (the Delta Effect) On the variation of cometary coma brightness with comet-Earth distance (the Delta Effect)

Jul 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993mnras.263..247h&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 263, no. 1, p. 247-255.

Astronomy and Astrophysics

Astronomy

1

Comet Nuclei, Cometary Atmospheres, Luminosity, Space Observations (From Earth), Distance, Encke Comet, Magnitude, Opik Theory, Comets, Comae, Brightness, Distance, Analysis, Earth-Based Observations, Halley, 1986Iii, Encke, Magnitude, Calculations

Scientific paper

This paper investigates the Delta Effect, a term that is taken to cover the quantitative variation of observed cometary brightness as a function of comet-Earth distance, Delta (as opposed to the more restricted definition, where it specifically applies to deviations of this variation from the inverse-square law). We investigate the Delta Effect in a variety of ways. Opik's assumption, that the eye integrates over a fixed solid angle, is questioned. A CCD image of Comet Halley (1986 III), taken using the Anglo-Australian 3.9-m reflector, is used to quantify the true variation of the integrated brightness as a function of R, the radial distance in the plane of the sky between the center of brightness of the coma and the point being observed. It is found that the quantity k varies as a function of the solid angle over which the detector integrates. These changes in k also vary as a function of Delta. These findings are applied to recent observation of Comet Halley. Observations of the apparent magnitude of Comet Encke, obtained between 1838 and the present, are analyzed. It is concluded that the area of sky over which the eye integrates cometary coma brightness is not constant, and that the generally accepted paradigm, that the only effect on the observed cometary brightness of changing observer-comet distance is the usual inverse-square law, is generally true.

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