The nearest star referred to as Proxima Centauri,is found to be regarding four light-weight-years away (the light from it takes regarding four years to succeed in Earth),or regarding twenty-three million million miles.Most of
the other stars that visible to the naked eye lie within few hundred light years of us.our sun,for comparision, is a mere eight light minutes away !The visible stars spreade all over the night sky,but are particularly concentrated in one band,which we call milky way.Now, the apparent brightness of a star depends on two factors:how much light it radiates (its luminousity),and how far it is from us.For nearby stars,we can measure the apparent brightness and their distance, and so we can work out luminousity.we know that
our galaxy is simply one in all some hundred thousand million which will be seen victimisation fashionable telescopes, each galaxy itself containing some hundred thousand million stars.we live in galaxy that
is regarding 100 thousand light-years across and is slowly rotating;the stars in its spiral arms orbit regarding its centre regarding once each many hundred million years.
stars sre to this point away that they seem to North American nation to be simply pinpoints of sunshine.we cannot see their size or shape.Different stars have different spectra,but the realtive brightness of
the different colors is usually precisely what one would expect to search out within the light-weight emitted by AN object that’s glowing red hot(In truth,the light emitted by any opaque
object that is glowing red hot has characteristic spectrum that depends only on its temperature -a thermal spectrum of its light).
In the 1920’s once astronomers began to appear at the spectra of stars in alternative galaxies,they found something most peculiar : there were the same characteristic sets of missing colours
as for stars in our own galaxy ,but they were all shifted by the same relative amount toward the red end of the spectrum.
In 1929 Hubbled published ,even the size of galaxy’s red shift is not random, but is directly proporrtinal to the galaxy distant from us .or in other word, the farther
a galaxy is that the quicker it’s moving away!
And that meant that universe could not be static, as everyone previously had thought,but is in fact expanding ;the distance between the different galaxies is growing all the time.The discovery
that universe is increasing was one in all the nice intellectual revolutions of twentieth century.Newton, and others, ought to have realised that a static universe would presently begin to contract underneath the
influence of gravity.But suppose instead that the universe was expanding .If it was expanding fairly slowly,the force of gravity would cause it eventually to stop expanding and then to start contracting.
The first figure shows that how the distance between two neighbouring galaxies changes as time increases.It starts at zero,increases to maximum,and then decreases to zero again.
In second cases point 4 shows separation between neighbouring galaxies in this model.It starts at zero and eventually the galaxies are moving apart at a steady speed.Finally there is third kind of solution in point 2 shows that galaxy starts at zero and and increases forever.
our galaxy and other has contained a large amount of ‘dark matter’ that we cannot see directly,but which we know must be there because of the influence of its gravitational attraction on the orbits of stars in galaxies.
If you want to get dive into Universe and its theory,then you should go through following books:
Enjoyed this article? Stay informed by joining our newsletter!