the universe One thing we know for certain about the Universe is that it is really really big because it holds all the stars in the sky and much much more In fact the Universe is so big we are not even sure if it ever ends Imagine setting off from Earth in a spaceship and travelling forever without hitting anything that’s how big the Universe is But hold on let’s start at the beginning First of all how was the Universe born The Universe exploded into existence 13 8 billion years ago in an event called the Big Bang Everything in the Universe was created in that moment all the stuff that makes the stars and planets and the energy that flows between them even space and time were created at the Big Bang No one really knows why it happened and to this day it remains one of the great mysteries of science The start is the Big Bang 13 8 billion years ago 13,799,000,000 years 377 thousand years 377,000 years after the Big Bang Atoms form and photons of light travel freely Through time the Universe spread out in all directions and began to take shape From the swirling energy tiny particles popped into existence After a few hundred thousand years they collected together into atoms the basic building blocks of everything we can see in the Universe Also at this time light was released and free to fly through the Universe Wowee
It wasn’t until hundreds of millions of years later that the atoms collected together into great clouds from which the first generation of stars was born These stars collected together into galaxies and the Universe started to become the one that we see in the sky at night today The Universe is still expanding now and will carry on getting bigger and bigger forever 200 million years 200,000,000 years after the Big Bang The first stars form 500 million years 500,000,000 years after the Big Bang The first galaxies form Fact You can hear the echo of the Big Bang yourself Just listen to a detuned radio one crackle in a hundred is made by leftover light from the Big Bang stretched over billions of years into radio waves 5
the birth of a star You may think that the only time you can see stars is at night but you’d be wrong our Sun is actually a star and you see it every day The Sun is quite an ordinary star and has kept a stable temperature and brightness since there has been life on Earth All the other stars are much further away than our Sun which is why they look so small in the night sky but they all have their own extraordinary stories to tell So how did they begin The stars formed out of clouds of hydrogen gas which were left over either from the Big Bang or from earlier exploded stars Over time gravity pulled this gas together into clumps where it started to spin and heat up This continued until the gas was dense and hot enough to combine and then in a flash of light a new star was born That is just incredible WOAH 6
types of stars Giant stars are very large which means they are extremely hot and bright Sadly this incredible power causes them to burn their fuel very quickly so they have a shorter lifespan than our Sun RED DWARF STAR Red dwarf stars are smaller than our Sun but live for an incredibly long time They are so small that they have a relatively slow and stable nuclear reaction at their cores that will last for hundreds of billions of years Brown dwarf stars are the smallest stars in the Universe They are not big enough to fuse hydrogen together but can be big enough to create other elements Brown dwarfs are very small and don’t give off much light so they are very difficult to discover GIANT STAR BROWN DWARF STAR MAIN SEQUENCE STAR Our Sun is known as a main sequence star and there are many others like it Main sequence stars make up 90 of the stars we can see and are the most likely to have planets that support life They are so beautiful Amazing 7
