As it reaches the Sun, a comet's tail gets bigger.  As it moves away from the Sun, the tail continues to gets bigger.  Comets are very long and wide.  The head is usually about 600,000 miles across.  The tail of the comet can be many miles long.  Comet tails are always facing away from the Sun.  When a comet leaves the inner part of the Solar System, it goes tail first.  

    The biggest comet yet, was recorded in 1811.  The head was 1.2 million miles in diameter, and the tail was 100 miles long.  The longest tail recorded was 205 million miles long.