Periodical comets :
The comets which have regular orbits round the Sun and occur at fixed intervals are called periodical comets. Halley’* comet is a periodical comet and is one of the most famous comets, which is due next in 2062. It is seen at intervals of 76 years. It was seen in 1910 and in 1986.
Non-periodical comets :
Such comets are seen very rarely and they are not sighted at regular intervals. There are records of observations of about 1000 comets. Some of these have been named. Comets become visible only when they travel close to the Sun. The ice melts and the gas and dust are swept back to form the tail. The tail always points away from the Sun.
