OUR PLACE IN THE UNIVERSE
The universe is thought to have been created in a vast explosion , the Big bang between10
to 15 billion years ago. All the matter that exists formed in a fraction of a second, in an infinitesimally small space , simultaneously hurtling outwards at incredibly high speed .As the Universe expanded , the matter flung out began to cool from the immeasurably high temperatures initially generated. As it cooled, tiny, fundamental particles combined to form protons and neutrons, which themselves formed atoms of gases hydrogen and helium These gases make up most of the universe today. Astronomers discovered that the universe is still expanding outwards from the original explosion ,although one day it may slow to a halt ,before contracting again in a final “Big Crunch”.
The scale of the universe
Looking out from our small planet, we can see that Universe is made up of successively larger structures. Earth is just one of nine planets orbiting the sun , and the sun is one among 200 billion
stars in the milky way galaxy. The Milkway is a large member of a cluster known as Localgroup, which is itself a member of our Local
Supercluster –one of around 50 such clusters which together make up the largest known structure in the universe.
The universe
The Big Bang cosmic afterglow and remains of the structure that is formed are captured in this from COBE , the cosmic Background Explorer satellite.
Supercluster
Between the vast supercluster of galaxies ,the universe contains voids-areas where no matter is detectable. the local supercluster to which our local group belong is so big that it takes light 100 million years to cross it.
LocalGroup
Our home galaxy ,the Milkyway ,is one of a cluster of galaxies in nearby space called the Local Group . This cluster is roughly 2.5 million light years across ,and contains the Andromeda as well as about 30 smaller elliptical galaxies.
Milky way
The sun is just one of 200 billion stars within the spiral disc of our Milky Way galaxy .Our solar system lies in one of the Milky Way s spiral”arm” which is why most stars are seen from Earth –looking along the Disc. –appear in a white band across the sky.
Solar system
Nine known planets ,together with smaller objects such as comets and asteroids ,form the Solar system in orbit around the sun. The outer curve of Pluto orbit stretches as far as 6 billion km from the sun .Planets orbit other stars than the sun : bodies as large as Jupiter orbit several nearby stars.
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