6 3 0 3 Micro MetreMilli Kilo ond never more and never less That consistency was also the reason why physicists have been defining metres as the distance covered by light within one 299 792 458th of a second since 1983 MEASURING GALAXIES USING THE DOPPLER EFFECT There are a number of methods we can use to measure distances We re all fa miliar with a metre stick and measuring tape while digital laser rangefinders have come to dominate work in the trades and around the home However when astronomers want to measure galactic distances these measuring methods are of little use We can determine the distances to galaxies using redshift 90 years ago American Edwin Hubble first observed that light from almost every galaxy is red shifted a phenom enon that physicists call the Doppler effect which we already know from the science of sound When a police vehicle with a siren is moving towards us we hear the siren as a high pitch but when it is moving away from us we hear a low pitch The colour red corresponds to these low pitches in light indicating that red shifted galaxies are moving away from us The stronger the redshift the further away the galaxy The Hubble Telescope in use since 1990 has unearthed galaxies that are more than 13 billion light years from Earth THE METRE IS THE UNIVERSAL MEASURE WE USE IT TO MEASURE OUR ENTIRE WORLD FROM GALAXIES TO ATOMS the measure of all things 27

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