How does a comet’s appearance change as it approaches the sun? why does this accur

Far out in space, the comets tail is short. As it approaches the Sun, the heat melts away some of the ice covering the surface. As it evaporates into space. a tail is formed behind the comet. Always, the tail is facing away from the sun.

Hope this helped. Have a great day! :D

Far out in space, the comets tail is short. As it approaches the Sun, the heat melts away some of the ice covering the surface. 

I hope this helps and have a wonderful day filled with joy~Timarra :)