posted by Vivek .
What is comet how it fall and why he look blue
You can think of comet as "dirty snowballs" that come from the outer regions of the solar system in highly eliptical orbits. Many only come once; others (like Halley's) return after many decades. As they approach the sun, some of the ice, other volatile chemicals and dust vaporize and are blown away by solar radiation, leaving a luminous "tail" of reflected sunlight and fluorescence. The blue color in the spectrum comes from C2 gas in the tail, but the eye sees the comet mostly the color white.