dipper@utastro.UUCP (Debbie Byrd) (11/20/85)
Today's the birthday of the man who found the key to measuring the greatest distances in our universe. More about Edwin Hubble -- in just a minute. November 20 Yardstick of the Universe At the turn of the 20th century, many astronomers believed that our galaxy, the Milky Way, was the one and only galaxy. They imagined that it contained all other celestial objects -- and that only empty space lay beyond it. They were proven wrong by Edwin Hubble -- who was born on this date in 1889 -- and who in 1924 found a way to measure the universe. With the 100-inch telescope at Mount Wilson in California, Hubble detected some very bright individual stars in the hazy celestial "cloud" in the constellation Andromeda. He recognized a particular class of stars called Cepheid variables. The Cepheids vary in brightness in a way that's regular and predictable. These variable stars were the key to measuring the universe. There's a relationship between the speed at which a Cepheid pulsates -- and its true brightness. The slower the pulsation, the brighter the star. By carefully measuring Cepheid pulsations, Hubble was able to calculate how bright the stars really were. He then could see how bright they looked from Earth -- take the difference -- and find the distance to the stars. Edwin Hubble did find the distances to stars in the so-called "cloud" in Andromeda. He was the first to prove that this cloud was really a separate galaxy -- located far beyond our galaxy's boundaries, some two million light-years away. Today, we know that most cloudy looking objects in the sky are separate galaxies -- gigantic collections of stars -- many of them as large or larger than our own Milky Way. Script by Deborah Byrd. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin