Expansion of universe

 

Astronomy is one of the oldest and most profound of the sciences. Edwin Hubble, an American astronomer found that stars are not uniformly distributed throughout space, but are gathered together in vast collections called galaxies. By measuring the light from galaxies, Hubble could determine their velocities. Hubble was the first to realize that all galaxies are moving away from us. Moreover, according to Hubble the further galaxies were from us, the faster they were moving away. The more distant the galaxy, the faster it was receding, with a speed proportional to its distance away (Hubble's law).The ratio of speed to distance is always the same number and is called the Hubble's constant.  The universe was not unchanging with time as everyone had thought previously. It was expanding. The distance between distant galaxies was increasing with time.

The expansion of the universe was one of the most important intellectual discoveries of the 20th century. It indicates toward an important point whether the universe had a beginning. If galaxies are moving apart now, they must have been closer together in the past. Hubble’s law sets a limit on the age of the universe. Because universe is continuously expanding, if we trace the expansion back to the beginning point, we can work out how long ago that was. It turns out to be approximate 15 billion years. Was this the beginning of the universe? The age of our Milky Way galaxy has also been calculated in two ways. First method is by studying the observed stages of evolution of different sized ancient stars in globular clusters.
A second method for estimating the age of our galaxy is based on the present abundances of several long-lived radioactive elements in the solar system. According to these calculations, the age of our galaxy is again comes out to be approximate 15 billion years.