Comets of the Enlightenment: Great Comets of the Seventeenth and Eighteenth Centuries

Abstract

Only under exceptional circumstances can any of the periodic comets appear bright enough to be easily seen with the unaided eye, and they rarely assume spectacular proportions in the night skies. A relatively small, intrinsically faint comet can appear bright and impressive in the night sky if its orbit brings it into close proximity with Earth; conversely, a far bigger, intrinsically brighter comet can appear small and faint if its perihelion takes place on the opposite side of the Sun to Earth. Optimum circumstances for any comet to occur is when it is at its intrinsically brightest near perihelion and in close proximity to Earth at the same time; a sizable apparent angular distance from the Sun at this time will mean that it will be seen in all its glory against a fairly dark sky background.