On a clear moonless night, we can seeVenus, Mars, Jupiter and Saturn shining brightly. As the earth goes around thesun, the planets and the stars change their position in the sky.
Alpha Centauri, the nearest star from earth,is four light years away. Our sun, meanwhile, is only eight light minutes away.The contemporary depiction of the universewas devised by Edwin Hubble in 1924.
Hubble disclosed that our galaxy, MilkyWay, is not the only one. There are many others and there are vast empty spacesbetween them. Our galaxy is 100,000light years across and it is rotating slowly. Hubble also postulated that thebrightness of a star depends on its luminosity and distance from earth. Hepublished in 1929 that the farther the galaxy, the faster is it moving away.
This means that the universe is not static. It could be expanding because thedistance between galaxies is growing over time. This discovery was one of the greatestdiscoveries in the twentieth century. Even Newton and Einstein did not think itpossible. It was only Alexander Friedmann who set about to explain thisexpansion. He derived his assumption on two arguments.
First, the universelooks identical wherever we look and second, this would also be true if we wereobserving from anywhere else in space. Friedmann’s prediction was supported byArno Penzias and Robert Wilson in 1965 when they tested a very sensitivemicrowave detector. They have tracked an extra noise which could come from outerspace since the frequency is the same for all directions. It may even come frombeyond the Solar System because the radiation is consistent throughout theyear. At the same time, Bob Dicke and Jim Peebles suggested that the glow ofthe early universe should be visible from earth in the present because itshould only be reaching us now. However, the expanding universe means that thislight had shifted immensely that it would only be perceived as microwaveradiation.