How did we discover that the Universe is Expanding? What does

it mean that it is expanding? This lecture introduces Hubble's Law,

the observational evidence that the Universe is systematically

expanding. As galaxies get more distant from us, the apparent speed

of recession gets larger in proportion. The proportionality is the

rate of expansion, called the Hubble Parameter (H0). This leads us

to the idea of expanding space, and the Cosmological Redshift, which

combined with the Hubble Law allows us a way to estimate very large

cosmic distances. We will take up the more thorny issue of the

Cosmic Distance Scale in tomorrow's lecture.

Recorded 2006 February 23 in 1008 Evans Laboratory on the Columbus campus

of The Ohio State University.