20 FAQs about the Universe

Read our experts' answers to some of your frequently asked questions.

  • 1. Is Pluto a planet?

    Pluto used to be called a planet but just a few years ago it was discovered that there were many other small icy objects like Pluto on the edge of the Solar System. So now they are called dwarf planets.

    Dr Marek Kukula


  • 2. Some people talk about the multiverse - does that mean there is an end to our Universe?

    We used to say the Universe was everything there was and so in that sense there would be no end. But actually if we look out into space, if we think about whether there is an end to the Universe, it could be that the Universe goes on forever.

    There is a bit of the Universe we can see, it is called the observable Universe which is the bit of the Universe that light has had time to reach since the Big Bang about 14 billion years ago. But outside that, there is definitely more Universe, we just do not know quite how much and it may even go on forever.

    Dr Tim O'Brien


  • 3. Are we ever likely to go back to the Moon?

    Man will definitely go back to the Moon. It is not a question of if, it is simply a matter of when. The Moon is a fantastic place to study, a four billion-year repository of the Solar System's history and we have a lot to learn. We will go there, we will colonise it and it will be an amazing and exciting time when it happens.

    Major Timothy Peake


  • 4. Can stars be different shapes and sizes?

    Stars cannot really be different shapes as they are so big their gravity is so strong which pulls them together and makes them more or less spherical. However they can certainly be different sizes. The Sun is about a hundred times bigger than the Earth as you measure across it. You could actually fit about a million Earths inside the Sun.

    But the biggest stars are several thousand times bigger than our Sun. If you put them into the Solar System they would actually extend right the way out to the orbit of Jupiter or even Saturn. Whereas very small stars such as some white dwarf stars are about the size of the Earth and neutron stars are only about the size of a city like Greater Manchester, about 20km across.

    Dr Tim O'Brien


  • 5. How many stars are there in space?

    In our galaxy, the Milky Way, it is thought there are around a few hundred thousand million stars, that is a few hundred billion stars. You can actually only see a few thousand of those if you go out at night and look at the stars on a clear sky, unless you are using a telescope. But scattered across the sky you might see the faint glow of all these other millions of stars - this is called the Milky Way.

    Our galaxy is not the only galaxy there is. In the observable Universe there are roughly a hundred billion galaxies. And each one of those galaxies has got maybe a hundred billion stars. So that basically turns out to be ten thousand million million million stars in the bit of the Universe we can see and actually the Universe might even go on beyond that.

    Dr Tim O'Brien


  • 6. Will the Sun really burn out?

    Yes it will. The Sun is burning fuel at a rate of 600 million tonnes a second and even though it is enormous, at that rate, eventually it is going to run out. But you do not need to worry because it will be in something like 5 billion years time.

    Professor Brian Cox


  • 7. How fast does a shooting star travel?

    A shooting star whizzes across the sky at about 50 thousand miles an hour. So that is much faster than a rifle bullet. It is actually not far above your head though - it is nothing to do with stars, it has actually got more to do with dirt than stars.

    They are grains of sand-sized things that come from the tails of comets. When they crash into the Earth's atmosphere they rush though the atmosphere very fast and they get very hot, just like your hands would if you rubbed them together. That makes them glow very brightly and they burn up in the atmosphere above our heads.

    Dr Tim O'Brien


  • 8. Why do stars appear to twinkle?

    Stars in the sky here on Earth appear to twinkle because the atmosphere causes their light to be distorted. It is very pretty but it is very annoying for astronomers because it blurs our images and that is why we have telescopes in space like Hubble.

    Dr Marek Kukula


  • 9. How far is the Sun from Earth?

    The Sun is about 150 million km away from Earth, which is 93 million miles. That is such a big number, it is a bit hard to imagine. But if you could imagine making a model in which the Earth was about the size of a marble, then the Sun would have to be about 200m away. It would be about the height of a person standing about 200m away from this marble-sized Earth.

    Another way of thinking about it is how long it takes the light to get here from the Sun. Light travels extremely fast, nothing can travel faster than it - about 300 thousand km a second. And that light takes about 8 minutes to reach us from the Sun.

    Dr Tim O'Brien


  • 10. What came before the Big Bang?

    The standard answer to what came before the Big Bang is that nothing can come before the Big Bang because the Big Bang was the start of everything - the start of time and the start of space. And it is a bit like asking a question: What is north of the North Pole? And the question does not make sense. So that is one way of thinking about it.

    But recently people have started to think about whether there has been more than one Big Bang. Maybe there is even more than one Universe. And so perhaps before the Big Bang, there was another Big Bang - we do not know.

    Dr Tim O'Brien


  • 11. Where do black holes come from?

    Black holes usually form when a very large star reaches the end of its life and explodes as a supernova and what is left at the centre is a black hole.

    Dr Marek Kukula


  • 12. Will everything eventually be sucked into a black hole?

    No, luckily. In fact I think black holes get quite a bad press, really, because they are pictured as cosmic vacuum cleaners that whizz around space hoovering everything up and everything gets sucked into them. In fact, it is not quite as bad as that. There is actually a massive black hole at the middle of our own Milky Way galaxy. But we are not being sucked into it because we are orbiting around and around it.

    I suppose, if you could get a massive pair of hands and get hold of the Sun and somehow squish the Sun down and turn it into a black hole then actually the Earth would not get sucked in, as it would carry on orbiting around it because the gravity of the Sun would not actually change. However, it would actually get dark eight minutes later and it would get very cold and it definitely would not be a good thing! But we would not get sucked into that black hole.

    Dr Tim O'Brien


  • 13. What shape is the Universe?

    We really have no idea what shape the Universe is because we cannot see an edge to it so it is a big mystery.

    Dr Marek Kukula


  • 14. Will man ever land on Mars?

    My dream is one day to retire to Mars! I think humans will go to Mars. I think humans in the future will live on Mars. We have a number of challenges facing us here on Earth and Mars can be the solution to many of them - overpopulation, growth of food. Mars is our sister planet and I think in the future we will live on Mars and utilise it to the good of mankind.

    Dr Maggie Aderin


  • 15. Why are some stars different colours?

    Some stars are different colours because they are actually different temperatures. So, in fact the hotter a star is, the bluer it looks and the cooler a star is, the redder it looks. So, in a way, that is quite handy because stars are so far away that if we wanted to take their temperatures, we would have to get in a spaceship and fly there and stick a thermometer in them. We do not have to do that - we just have to measure their colours.

    The interesting thing there is that it is the opposite of what you might normally think. So if you go in a physicist's bathroom, then just be careful because the hot taps have blue labels on them and their cold taps have red labels!

    Dr Tim O'Brien


  • 16. How big is the biggest star?

    As you can imagine, stars are so far away it is quite hard to be certain about exactly how big they are. But we think that one of the biggest stars is a star called VY Canis Majoris which is about 4,000 light years away. And it is about 2,000 times bigger than our Sun. So if you plonked it in the middle of our Solar System it would actually extend out to the size of the orbit of Saturn.

    It has a funny name - VY Canis Majoris. It is actually in the constellation of Canis Major, the Great Dog. And the VY bit is because it varies or changes in brightness and we have a system of calling them after all the letters of the alphabet. So it just lets us distinguish it from other stars in that same constellation.

    Dr Tim O'Brien


  • 17. Do stars have babies?

    I suppose you could say that stars have babies and those babies are the planets that orbit around them. Planets are formed by the debris that is left over after a star has formed. And they orbit around a star a bit like little ducklings going around a mother duck!

    Dr Marek Kukula


  • 18. Why does the Moon orbit the Earth?

    The Moon orbits the Earth because of gravity. And gravity is the force that holds everything in the Universe together. It keeps your feet firmly on the ground here, it keeps the Moon in orbit around the Earth and it keeps the Earth in orbit around the Sun.

    Dr Marek Kukula


  • 19. Why does Saturn have a ring around it?

    Nobody really knows why Saturn has such a beautiful system of rings around it. One possibility is that it is the debris from a Moon that was smashed apart billions of years ago. But we really do not know the answer to that.

    Dr Marek Kukula


  • 20. Why can you see the Moon sometimes in daytime?

    We have all grown up seeing the Moon shining brightly in the night-time sky. But it is actually up in the day-time sky quite a lot. In fact the Moon orbits the Earth about once every 28 days, roughly once a month. So if you think about it, half the time it is going to be on the opposite side of the Earth to the Sun and therefore it is in the night-time sky. But the other half of the time it is in the same side of the Earth as the Sun is and so it is actually up in the day-time sky.

    So funnily enough, the Moon's up at night half the time - about two weeks of the month and the other half of the time, it can be seen during the day. And the trouble is it is hard to spot because the day-time sky is so bright, but just keep an eye out for it.

    Dr Tim O'Brien


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