Why is light from stars and planets considered to be parallel light?

The stars and planets are at a very far distance. Each point on the star and planet is direct or indirect source of light. Light diverges from every point. But the distance is so large that by the time it reaches, this divergence is negligible and all the rays are considered to be parallel rays of light.  

Because they are very far away from Earth and are not point source of light

Explanation:

We know that the stars emit their own light while planets reflect the light of the Sun/star. If the source of light is a point, the light will emit in all direction and no rays will be parallel but we know that neither stars nor planets are point object. So light will be emitted out from each point. This makes the divergence less apparent.

Also the distance between the stars/planets and Earth is huge which makes the light rays to appear parallel as the divergence is too little to be observed.

sonar - device which is used to find the submit submarines, sankalp ship. sonar waves consists of a transmitter and detector which are installed in the observation centre on board of a ship. the ultrasonic waves are sent into the sea at high frequency about 1000 khz in all direction.

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.