an increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move toward (or away from) each other.

a unit of astronomical distance equivalent to the distance that light travels in one year, whihc is 9.46 x 6 trillion miles.

energy that is transferred by electromagnetic radiation, such as light, x-rays, gamma rays, and thermal radiation, which may be described in terms of particles or waves.

scientists in the field of astronomy that stury stars, planets, moons, commets and galsxies.

the flow of energy at the universal speed of light through freespace or through a material medium in the form of the electric and magnetic fields that make up electromagnetic waves such as radio waves, visible light, and gamma rays.

the range of wavelengths or frequencies over which electromagnetic radiaton extends.

an event that describes how the universe expanded from an initaial state of high density and temperature.

the distance between successive crests of a wave, especially points in a sound e or electromagnetic wave.

nonluminous material that can take several form including weakly interacting particles or high-energy moving particles created soon after the Big Bang.

the force that attracts a body toward the center of the earth, or toward any other physcila body having mass.

the displacement of spectral lines toward longer wavelengths in radation from distant galaxies and celestial objects.

a theoretical repulsive force that counteracts gravity and causes the universe to expand at an accelerating rate.

the rate at which a vibration occurs that constitutes a wave, either in a material, or in an electromagnetic field, usaully measured per second.

a system of millions or billions of stars, together with gas and dust, ehld together by gravitational attraction.