PLANET: A celestial body that revolves around a star. Derived from Greek work “PLANETES” which means wanderer.

STAR:   A natural luminous body burning gas which is held together by gravity.


  • Planet earth and life on it.
  • Philosophically; the whole of the physical universe, “world” of an individual.
  • Comes from old English; “weorold”; wer-man, eld-age; which means “age of man”.
  • Distinguishes entire planet or population from any particular country or region.

UNIVERSE: Derived from old French word “unvers” which is in turn derived from Latin “Universum”. Defined as all existing matter and space considered as a whole.

COSMOS: Implies viewing the universe as a complex and orderly system (or) entity. ( the opposite of chaos). First used by Pythagoras for the (implying) order of the universe.

COSMOLOGY: Understanding of reasons for nature’s existence and significance. Study of Cosmos.

COMET: A chunk of ice and rock originating from the outer solar system, often accompanied by a coma and tail.

ASTEROID: A rock in orbit; the larger chunk of rocks.

METEOROID: A space rock that is bigger than a dust grain but smaller than an asteroid.

METEOR:  The streak of light when a space rock enters the atmosphere and starts burning up (falling star).

METEORITE: If a meteor doesn’t entirely burn up. A piece of space rock that lands on earth are called as a meteorite.

GALAXY:  A system of millions or billions of stars and planets together along with gas and dust held together by gravitational attraction.

NEBULA:  Interstellar cloud of dust, hydrogen, helium and other ionized gases.

MULTIVERSE:  Hypothetical group of multiple universes.

 PARALLEL UNIVERSE:  Different universes within multiverse.

BLACK HOLE: A concentration of mass so dense that nothing, not even light can escape its gravitational pull once swallowed.

NEUTRON STAR:  A celestial object of very small radius (~30km) but which is extremely dense composed of closely packed neutrons.

QUSARS (Quasi Stellar Radio Source): Extremely luminous active galactic nucleus.

BLAZAR: A feeding supermassive black hole producing high energy jets which are viewed face-on from earth.

DARK MATTER:  Invisible matter.

DARK ENERGY:  Force that repels gravity.

ANTI MATTER: Opposite of normal matter.

STRING THEORY: earlier referred as a 1-d entity having dynamic properties similar to those of flexible elastic string.

SUPER STRING THEORY:  Supper symmetry + string theory.

SUPERSYMMETRY:  Each particle from one group (fermions, bosons) would have an associate particle.

GALAXY NAMING is based upon two categories.

  • Messier( named after Charles Messier)
  • New general category (NGC).

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