why we don't see comets until they are mear the sun?
Because (1) the sun, when close, comet by reflection. (2) The sun also evaporates the icy head of the comma faster when it is closer to the sun, to provide more material to reflect light.
(3) A comet tends to be closer to the Earth when it is near the sun, compared to when it is beyond the orbit of Jupiter. This makes it appear brighter and larger.
The reason why we don't see comets in the sky until they are near the Sun is due to their characteristics and their orbits. Let me explain:
1. Composition: Comets are made up of a combination of ice, dust, and other organic compounds. When a comet is far away from the Sun, these components remain frozen and relatively inactive. As the comet approaches the Sun, the heat causes the ice to vaporize, which creates a glowing coma (the hazy cloud around the nucleus) and a tail. This is when the comet becomes visible from Earth.
2. Orbit: Comets typically have highly elliptical orbits, which means they spend most of their time far away from the Sun in the outer regions of the solar system, such as the Kuiper Belt or the Oort Cloud. It is only when they enter the inner solar system that they come close enough to the Sun for the heat to activate them and make them visible.
So, in summary, we don't see comets until they are near the Sun because their icy composition needs the Sun's heat to vaporize and create the distinct coma and tail that make them visible from Earth. Additionally, their orbits keep them in the outer regions of the solar system for most of their journey.