Pictures of two newly discovered Sun-grazing comets were released this month by the National Center for Atmospheric Research's High Altitude Observatory in Boulder, Colo. A coronagraph telescope orbiting Earth aboard a National Aeronautics and Space Administration spacecraft collected the images of the comets on October 5 and 17, 1987. The spacecraft is part of NASA's Solar Maximum Mission (SMM), and the comets have been named SMM 1 and SMM 2.
Sun-grazing comets do not form a strictly defined group, but any comet that comes within ∼0.01 AU of the Sun's center can be considered a sun-grazer. These comets have been thought to be fairly rare, but as Brian Marsden of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., points out, sightings of them seem to have a clumped distribution in time. Several Sun-grazing comets were reported in the late 17th century and again in the mid and late 19th century, but with the exception of one in 1945, no more were seen until the 1960s. Eight more have been spotted since the first space-based observation of a Sun-grazing comet in 1979.