Some Important Definitions, Cosmology, Universe, Galaxy, Star, Solar System

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Some Important Definitions


Cosmology is the science of the cosmos or universe. OR Cosmology is the branch of physical science which deals with the Universe.


The universe is the sum total of all that exists, or has existed, both in space and time.


A galaxy is a system of many thousands of millions of stars together with inter-stellar gas and dust. OR Galaxy is a fundamental unit of the universe. It is composed of hundreds of thousands of stars together with intra-stellar gas and dust.


Those heavenly bodies which are luminous and produce their own energy by nuclear reactions are called stars.

  • Proximal Centauri second nearest after Sun to the Earth.

  • Antares is one of the largest stars known.

Solar System

A tiny system of our galaxy which consists of the /sun, a planet and their satellites, thousands of miniature planets called asteroids, meteoroids, comets, interplanetary dust and plasma.


Those heavenly bodies which revolve round the planets are called satellites.


In astronomy, the term eclipse simply means the obscuring of one heavenly body by another, particularly that of the sun or a planetary satellite.

Lunar Eclipse

A condition when the earth comes in between the sun and the moon and throws its shadow on the moon is called lunar eclipse.

Solar Eclipse

A condition when the moon comes in between the sun and the moon and throws its shadow on the moon is called Solar Eclipse.


Astrology is the interpretation of the influence of planets and stars on human lives.


Small, irregular shaped rocky objects which orbit the sun between the orbits of Mars and Jupiter are called Asteroids.


Tiny chunk of material floating in space which can also enter the earth’s atmosphere and become meteor are known as meteorites.


The bodies mainly composed of ice and dust which revolve round the sun are called comets.