ANSWER: (click and hold) Because they are moving away from us, the spectra of other galaxies are shifted toward the red, or long wavelength end of the spectrum.

ANSWER: (click and hold) The spectra of the farthest galaxies are "redshifted" to the greatest extent. This relationship is known as Hubble's Law.

ANSWER: (click and hold) It means the universe is expanding uniformly. No matter in which direction we look, the rest of the universe is moving away from us at a rate that depends directly on its distance from us.

Question #4:

Why do Cepheid variable stars make good "standard candles" for determining the Hubble constant?

ANSWER: (click and hold) Cepheid variable stars vary in brightness in a way that is directly related to their brightness. Therefore, by measuring a cepheid's period, scientists can determine its brightness, and by comparing this with its brightness from earth, they can then calculate its distance.