Planets

A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.
According to The International Astronomical Union (IAU) a celestial body can be called planet when it
(a) Is in orbit around the Sun or any star forming a solar system.
(b) Has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium shape.
(c) Has cleared the neighborhood around its orbit.


In order to understand further it would be necessary to observe our solar system where along with earth, several other planets are revolving around the sun which is a star hence forming their own orbits.
Earlier it was assumed that planets appear to change location in the sky night from night, whereas stars seem not to move appreciably from one night to the next. So it was thought that noticeable change in location from one night to the next meant the object was a planet. However with the passage of time those measures were obsolete yet there are several differences between these two celestial bodies.

Differences Between Planets and Stars

The basic difference between a star and a planet is that a star emits light produced by a nuclear reaction in its core, whereas a planet only shines by reflected light. apart from that there are several other differences such as

• A star is a mass of gas held together and given its shape by its own gravity. Gravity is constantly squeezing the star, trying to make it collapse. This collapse is prevented by the radiant pressure from the hot gas in the star's interior. This is called hydrostatic support, or equilibrium. On the other hand planets are massive enough to be rounded by its gravity.
• Stars can give their own light while planets cannot. They can only reflect light coming from stars that's why we can see them. Planets never give their own light.

• Also, stars are made of gas and have a greater gravitational pull. In addition the Stars are hot balls of hydrogen and helium, while planets are the masses that orbit them.
• The planets move relative to stars on celestial sphere while the relative positions of the stars are fixed on celestial sphere.
• The nearer and larger planets appear as disks in telescope while the stars appear as points of light, even through the telescope. Twinkling is another unique characteristic of star while the planets do not twinkle as they only can reflect the light.