Our sun and the nearby stars are all parts of a vast collection of stars called the MILKEY WAY GALAXY. For a long time it was thought that this was the whole UNIVERSE . In 1924 that the American Astronomer Edwin Hubble demonstrated that ours was not the only galaxy. There were, in fact many others,with vast tracks of empty space between. In order to prove this he need to determine the distance between to thses other galaxies. 1.DETERMINATION OF STARS : We can determine the distance of nearby stars by observing how they change position as the Earth goes around the sun. But other galaxies are so far away that, unlike nearby stars, they really do appear fixed. Hubble was forced,therefore, to use indirect methods to measure the distances. 2.Factors On which the brightness of Stars depends: i.)LUMINOSITY ii.)How FAR IT is For nearby stars we can measures both their apparent brightness and their distances, so we can work out their luminosity. Finally some i
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