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SAI INTERNATIONAL SCHOOL
Class 8
Lesson Notes
Subject-Physics
CH- Stars and Solar system
Subtopic- Solar System

 The Solar System:
o It consists of the Sun and other celestial objects present in the space
revolving around the sun.
o The gravitational attraction between the Sun and these objects keeps
them revolving around it.
o The various entities like planets, meteors, comets, etc. are part of our
solar system.
 The Sun:
(i) The Sun is the nearest star among all the stars present in the universe.
(ii) It is the main source of heat and light for all the planets specially Earth.

 The Planets: Planets are heavenly bodies revolving around Sun in a fixed orbit.
o They do not have light of their own. They merely reflect the sunlight that
falls on them.
o The planets keep changing their positions with respect to the stars.
o Period of revolution: It is the time taken by planet to complete one
revolution around the sun.
o Period of rotation: It is the time taken by planet to complete one rotation
on its own axis.

Differences between stars and planets

STARS PLANETS

Stars are the astronomical objects, that Planets refer to the celestial object that has a
emit their own light, produced due to fixed path (orbit), in which it moves around the
thermonuclear fusion, occurring at its star.
core.

They have their own light. They do not have their own light.

They are big in size They are small in size as compared to stars

They have high temperature Planets have low temperature compared to
stars.

Stars twinkle. Planets do not twinkle.

Hydrogen, Helium and other light Solid, liquid or gases, or a combination of
elements. them.