What is a comet?
A comet is a small Solar System body made largely of ice, dust and rock. As it approaches the Sun, its warming surface releases gas and dust, forming a visible coma and tail. Despite its name, it is not a star.
Nucleus, coma and tail
The solid nucleus lies inside a cloud of gas and dust called a coma. Sunlight pressure and the solar wind steer released material, so a tail generally points away from the Sun rather than necessarily behind the direction of travel. Dust and ion tails can look different. A comet may be very faint far from the Sun before strong outgassing begins. Solar gravity chiefly determines its orbit, though the escaping material may alter its motion slightly.
Origins and scientific value
Many short-period comets are associated with the Kuiper Belt beyond Neptune; very long-period ones are linked to the distant Oort Cloud. Their material can preserve clues about early Solar System conditions, although compositions vary. Earth crossing particles shed along a comet’s orbit may produce a meteor shower. A meteor is the bright trail of a particle entering the atmosphere; a piece reaching the ground is a meteorite. Orbital observations track impact risks; a bright tail does not mean an impact is imminent.