Vocabulary#11 Galaxies and Beyond

Galaxy:A large group of stars held together by gravity.
S:The stars orbit the center of their galaxy.

Milky Way:Our home galaxy.
S:We live in the Milky Way.

Spectrum:A band of colors made when white light is broken up.
S:The light produce spectrum.

Expansion Redshift:The shift of spectrum of a galaxy toward longer(redder)Wavelenght due to the expansion of space.
S:It is called redshift because the light`s spectrum has been shifted to longer Wavelenght.

Big Bang:The beginning of the universe,when the density of the universe was very high.
S:The universe has expanded ever since Big Bang.

Background Radiation:Electromagnetic radiationleft over from the Big Bang.
S:The Background radiation was discovered in the 1960s.

Quasar:An extremely bright,extremely distant,high-energy source.
S:Quasar must be very,very old.