Cosmology

State the definition of a light year:the distance light travels in one year

Show by calculation that 1 light year is equal to 9.46 x 1015 metres:

D=VT

D= (3x108 )x(365x24x60x60)

D=9.46 x 1015

State what is meant by the following:

• A star: a massive ball of hydrogen gas undergoing nuclear fusion at its core

• A planet (three criteria):a spherical ball that orbits a star and has cleared its local neighbourhood

• A dwarf planet:a Spherical ball of rock or gas that orbits a star but hasn’t cleared its local neighbourhood

• An exoplanet: a planet outside our solar system

• A moon: a natural satellite of a planet

• A comet / asteroids / meteor :other lumps of rocks and ice that orbit a star

• A solar system :a star with planets and asteroids orbiting it

• A galaxy: a large cluster of stars

• The observable universe:everything we can see from earth

• The Universe:everything that

exists has existed or will exist