CometsWhy do comets have tails? Why do the tails point away from the Sun?

Comets have tails (two of them, in fact) because of stuff coming off the comet's core.  One of the tails is made of dust.  The other tail is made of gasses.

Both of these tails point more or less away from the sun.  The reason for this has to do with what we typically call the solar wind.  There is all kinds of radiation coming off the sun and heading off into space in all directions.  This radiation "blows" all the dust and gas that make up the tails.  Because of this, the tail points away from the sun just as a flag blows away from the source of the wind here on Earth.