Comets

The first observation of a comet through a telescope was made in 1618. Previously, comets were discovered with the naked eye. Today, most new comet discoveries are made from telescopic photographs and electronic detectors; many comets are discovered by amateur astronomers, and are named after their discoverers.

The long-focal-length, refracting telescope—the primary astronomical observation tool of the 1800s—worked well for direct viewing although, with the relatively insensitive photographic emulsions of the period, it did not collect sufficient light to allow astronomical photography. In 1858, an English artist, William Usherwood, used a short focal-length lens to produce the first photograph of a comet. In 1864, by using a spectroscope, an instrument which separates the wave lengths of light into spectral bands, Italian astronomer Giovanni Donati (1826–1873) first identified a chemical component in a comet's atmosphere. The first cometary spectrogram (photographed spectrum of light from a comet) was taken by English amateur astronomer William Huggins (1824–1910) of London in 1881.

The early twentieth century saw the development of short-focal-length spectrographs which, by the 1950s, allowed identification of several different chemical components in a comet's tail. Infrared spectrography was introduced in the 1960s and, in 1983, the Infrared Astronomy Satellite (IRAS) began gathering information on cometary dust particles that was unobtainable by ground-based technology. Today, observations are also made by radio astronomy and ultraviolet spectrography.