Question

Why does the tail of comet looks longer when it s nearer to the sun and shorter when it is away from sun?

Answer 1

Solar radiation and solar wind increase as distance to the sun decreases...

Explanation:

Comets are commonly described as just big balls of ice. Solar radiation and solar wind (particles streaming out from the sun) heat the surface of the comet, causing sublimation, and then the sublimated particles from the melted ice are knocked off the comet and forced away. This forms the tail of the comet, and the intensity of this effect increases as the comet gets closer to the sun.