THE EXPANDING UNIVERSE

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 intresting facts comes: If we knew the luminosity of stars in ithers galaxies, we could work out their ditance by measuring their apparent brightness. Hubble argued that there wre certains types of stars that always had same luminosity when they were near enough for us to measure. If we could do this for number of stars in the same galaxy, and our calculations always gave the same distance, we could be fairly confident of our estimate. I n this way, Edwin Hubble worked out the distances to nine different galaxies.

Source:BookThe THeory Of EVERYTHING