dipper@utastro.UUCP (Debbie Byrd) (06/15/85)
Nearly all the galaxies outside our Milky Way appear to be moving away. More -- after this. June 15 The Hubble Constant The galaxies in our expanding universe are moving away from each other. They get farther apart as space itself expands from the Big Bang -- a primordial explosion thought to have occurred many billions of years ago. From where we sit, on a planet orbiting a star in a galaxy, almost every other galaxy is seen moving away from US. What's more, the galaxies obey a fundamental rule -- the more distant the galaxy, the faster it moves away. Astronomers use this fact to determine the DISTANCES to remote galaxies in our universe. They measure how fast a particular galaxy is moving outward, then divide by a number called the Hubble constant, to find the distance to the galaxy. The Hubble constant simply relates the speed of a receding galaxy to its distance. In addition to helping us find the distances to the galaxies. it also gives a clue to the age of the universe. Knowing how fast the galaxies are moving apart, we can figure backwards to find when they must have been very close together, at the start of the expansion -- just after the Big Bang beginning of our present universe. Unfortunately, the exact value for the Hubble constant isn't known. The two leading estimates disagree with each other by 100 per cent! Also several other considerations must be taken into account. But after all the dust has settled, many astronomers do try to use the Hubble constant to estimate the age of our universe -- and find it to be between 10 and 20 billion years old. Script by David Slavsky and Deborah Byrd. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin