The Universe

If one looks at the sky on a clear,moonless night,the brighest objects one sees are likely to be planets Venus,Mars ,Jupiter ,and Saturn.There will also be a very large number of stars which are just like our own sun much farther from us.
Some of these fixed stars do,infact appear to change very slightly their positions relative to each other as the earth orbits around the sun;they are not really fixed at all.This is because they are comparatively near to us. As the earth goes around the sun,we see them from different positions against the background of more distant stars.The change very slightly their positions
relative to each other as the earth orbits aroundnearest star,called PROXIMA CENTAURI,is found to be about four light -years away,or about twenty -three million million miles. the visible starsWAY.
Only a few decades later,the astronomer,Sir William hershell,confirmed his idea by painstakingly cataloging the positions and distance .If one looks at the sky on a clear,moonless night,the brighest objects one sees are likely to be planets Venus,Mars ,Jupiter ,and Saturn.there will also be a very large number of stars which are just like our own sun mch farther from us.
Some of this fixed stars do,infact appear to change very slightly their positions relative to each other as the earth orbits around the sun;they are not really fixed at all.This is because they are comparatively near to us. As the earth goes around the sun,we see them from different positions against the background of more distant stars.The nearest star,called PROXIMA CENTAURI,is found to be about four light -years away,or about twenty -three million million miles. the visible stars
spread all over the night sky but are particularly concentrated in one band,which we call the MILKY WAY.Only a few decades later,the astronomer,Sir William Hershell,confirmed his idea by painstakingly cataloging the positions and distances of vast number of stars even then the idea gained acceptance only early this century.Our modern picture of the universe dates back to only 1924,when the american astronomer EDWIN HUBBLE demonstrated that ours was not only the galaxy. So he figures out a method in acceptance to prove his method,now the apparent brightness of the stars depends upon two factors how much light it radiates(its luminosity).conversely,if we know the luminosity of stars in other galaxies ,we could work out their distance by measuring their apparent brightness HUBBLE noted that these type of stars always have the same luminosity-and so calculate the distance to that galaxy.if we could do this for a number of stars in that galaxy,and our calculations always gave the same distance we would be fairly confident of our estimate..
In this way EDWIN HUBBLE  work out the distance to ine different galaxies .we know that our galaxy is only one of some hundred thousand million that can be sen using modern telescopes,each galaxy itself containing some hundred thousand million stars of vast number of stars even then the idea gained acceptance only early this century.Our modern picture of the universe dates back to only 1924,when the american astronomer EDWIN HUBBLE demonstrated that ours was not only the galaxy.There were many other ,with vast tracts of empty spaces between them.So he figures out a method in acceptance to prove his method,now the apparent brightness of the stars depends upon two factors how much light it radiates(its luminosity).conversely ,if we know the luminosity of stars in other galaxies ,We could work out their distance by measuring their apparent brightness hubble noted that these type of stars always have the same luminosity-and so calculate the distance to that galaxy.if we could do this for a number of stars in that galaxy,and our calculations always gave the same distance we would be fairly confident of our estimate..In this way EDWIN HUBBLE  work out the distance to ine different galaxies .we know that our galaxy is only one of some hundred thousand million that can be sen using modern telescopes,each galaxy itself containing some hundred many other ,with vast tracts of empty spaces between them thousand million stars .