# Nine Planets - Astronomy Question

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#1 What's at the other side of the universe?

This can really be a lot of different answers. In relation to what is at the edge of our universe the popular opinion is that because the universe is an ellipsoid (a sort of 3D oval) gravity and the sheer size of it will always make you feel like you're at the centre. If you actually had enough rocket fuel to get from one end to the other- which would be a LOT of rocket fuel- you'd actually be looking back at yourself because of the way the light bends around the edges of the universe. However, this is all dependant on whether or not you have a clear view across the universe- which would be really difficult! Other people argue that there is no 'side' of the universe and therefore you can't ever see what's at the edge of it or outside of it because it's constantly moving an expanding.

#2 What is a wormhole?

A wormhole isn't technically a real thing, as such. It's more of a theory based on the idea that if we connect a load of black holes together we'd be able to create a sort of portal to other parts of the universe and possibly to other dimensions completely. If you ever saw the TV series "Black Hole High" that dealt with the theory that a collection of worm holes could take you through time as well as to alternate world. Albert Einstein's special theory of relativity states that a wormhole is mathematically possible, although they'd probably collapse within a few seconds. Also, when you consider the force of a black hole, jumping into a collection of them might not be a very wise idea.

#3 What's the inside of the earth made from?

The earth is made up of several different layers, starting with the crust which is the rocky outer surface and is around 80km thick. Underneath this the thickest part is the mantle, which although it's a solid rock, it does actually move around the inside of the earth at about the same speed your finger nails grow. Then you have the proper inside of the earth- the outer core and the inner core. Both of these are really really hot and the outer core is made up of liquid iron and nickel that swirls around the centre of the earth. The centre is a solid ball of iron and nickel that is roughly 6000 miles inside the earth.

#4 When is the best time to observe the features of the moon?

The moon is a particularly interesting body and you could go out every night for a month and always see something different on it. The best time of night to do this is when the moon is right over head because at this point it's closer to earth and looks a lot bigger. When it's more on the horizon it will be more distorted as you have 100's more miles to look across. In regards to phases of the moon, the best time to see sharp and defined details will be when the moon is going from new to full. If you follow the trail of light as it moves across the dark you'll see very interesting features and marks. A full moon isn't as good as it sounds as the brightness can often impair the detail.

#5 What's inside a black hole?

Probably everything you ever lost under your bed and couldn't find again. No-one really knows for sure what's inside a black hole, because no-one's ever been inside one, and you can't see inside one from the outside- obviously if you went into one there's a strong chance you're not going to be coming out again! Inside a black hole the force of the gravity pulls on anything that comes inside it and distorts it in a process called spaghettification. Because of this any living creature or organism that went into a black hole would be distorted and stretched apart in milliseconds and would die painfully, but instantly.

#6 What do you call an exploding star?

An exploding star is a schoolboy term for a Supernova star. When a star itself explodes it forms what's known as a nebula. When a supernova 'explodes' it causes a burst of luminous radiation which can outshine an entire galaxy before fading over a period of weeks. Amazingly, the supernova emits as much energy in this one explosion as the sun does in its entire lifetime. Nova comes from the Greek word "novae" meaning new and refers to the fact that when the supernovas glow it looks like a bright new star in the sky.

#7 Why does the sun look red when it sets?

Do you remember the experiment in school where you shone light through a prism to refract it and make a spectrum of colours on the table or onto a sheet of paper? The same sort of thing happens in the atmosphere when the sun sets, but on a much grander and more technical scale. The water molecules in the atmosphere act as a huge prism and as the sun sets down the earth towards the horizon the light goes red like the top of the EM spectrum. The light is then scattered due to dust particles in the air which then spreads it across the entire thing.

#8 What's the different between a partial and total lunar eclipse?

Although this sounds like it will be a really complex and scientific explanation a partial and lunar eclipse are exactly the same. The only different is the amount of moon that is covered up in the process. In a partial eclipse part of the sun is still shining on the moon, this can mean that the moon is practically covered, but a little bit of it is still visible, or it can mean that only a small part of it is covered. A total eclipse is when the entirety of the moon is covered and everything goes eerily dark. Both can last roughly a few minutes before they pass and sometimes they can be viewed for one or two nights depending on the kind. The same applies for a solar eclipse.

#9 What would happen if a comet entered our atmosphere?

If a comet entered our atmosphere it would be the end of the world completely, because of this a comet entering the atmosphere has been given the title of "Extinction Level Event" or ELE by Astronomers. Needless to say it's a big deal. There's a crater in Arizona that was caused by a refrigerator sized meteor and is about a mile wide and half a mile deep. A comet is much bigger than a meteor and to give you a rough estimate, imagine the state of Rhode Island. Not only would the impact kill everyone, the tremors and aftershock would send millions of tonnes of soil up in to the atmosphere and block out the sun- causing an ice age on the side of the globe that wasn't obliterated in the initial blast. The heat of the comet would quite literally set the atmosphere on fire too and if it hit the sea all the water would vaporise immediately and the rest would cause a massive tsunami.

#10 How big is space?

This is very difficult to calculate as we haven't even scratched the surface of what's in space yet. Our own universe is billions of light years in size and if we wanted to measure the entire expanse of space we'd need to map out all the other galaxies in existence and even some that we don't know exist yet. However, this is a lot harder than it sounds- and it sounds pretty hard to begin with- because a lot of the light we see in space that we think is a galaxy is actually just the light left behind from a galaxy that ceased to exist even before earth was formed.

#11 What are the different kinds of stars?

There are many different kinds of star, such as drawf stars, binary stars and stars like the sun that are so huge they have their own classification entirely. Stars, however, are universally grouped according to their spectral classification. This refers to its size, composition and colour. An O star is 70,000 degrees Fahrenheit and a bluish colour, a B star is a pale blue and is roughly 34,000 degrees, an A star is white and 15,000 degrees and a G star is yellow and around 9400 degrees. This means that the sun is a G star and is actually cooler than most other stars in the sky, it's just a lot bigger. A K star is orange and 7,200 degrees and finally an M star is red and just 4,900 degrees. So, the brighter and closer to white a star is, the hotter it can be and the higher up in the scale it is.

#12 Why do we weigh less on the moon?

The basic answer to this is the lack of gravity on the moon. The more technical answer is that you weight exactly the same as you do on earth, it's just that the gravitational pull on your body is less so your mass is lower. Your weight stays exactly the same but it is just handled differently with lower gravity. Because the moon is smaller than earth, the gravitational pull is about one sixth as strong as it is on earth. If you want to work out your moon weight, simply multiply your weight in pounds by 0.016. If you really want to feel light, however, go to Pluto. Because it's so small you times your earth weight by 0.059! Beware of Jupiter and Neptune though, as they have a gravitational pull that's bigger than earth's, so you'd feel heavier.

#13 What was here before the big bang?

This is a really easy question to answer because quite simply there is no answer. We don't currently have the technology or intellectual capacity to fully comprehend the big bang theory and what came before it and at the moment everything that's out there is just speculation. A major one is creation theory, where in Christian mythology God was created from nothing and made the earth, and other religions have the same sort of story with their Gods creating a world for human's beneath them. However religion and fact are different for everyone and sometimes belief fuels what we thing and sometimes scientific fact fuels what we think. So, in answer, we don't know.

#14 How long would it take to walk to the sun?

It's roughly 93 million miles to the sun from earth, so if you were walking constantly at 4mph it would be 23,250,000 hours. This is around 2,654 years so you'd need several life times to do it in! Not to mention you'd frazzle up and die once you got too close. If you had a car it would be a lot easier, if you were going at 55mph, just under national speed limit, you'd only need 193 years to get there. Assuming you had unlimited petrol and no breaks whatsoever, of course.

#15 How long will the sun last?

Because the sun is a star it follows the same sort of life span as other stars in the galaxy. Taking into account its size, the sun will live to be roughly 12.3 billion years old. At the moment it is around 4.5 billion years old, so has about 7.8 billion years left. When it becomes 12.2 billion years old it will become a red dwarf star and in the next 100 million years of its life it will become a white dwarf. It will definitely outlive earth, however, because when it's a red dwarf it will consume mercury and Venus and therefore leave the earth so hot we won't be able to live on it. The white dwarf is caused after the sun gets rid of all the outer layers in a nebular explosion, it will then cool off and fade into nothingness.

#16 What causes sunrise and sunset?

Ironically it's the earth turning around that makes the sun go up and down in our skies. It's a little bit odd when you think of it in that sense, but remember the earth itself is rotating as well on the axis as it rotates around the sun so this makes the sun appear to move up and down in our sky as the earth turns around to give us night and day but also the seasons as well when we move around the sun. Imagine a ping-pong ball on a stick turning as it is rotated around a basketball. Then there's the moon that goes round the earth and controls the tides and other things. As it rotates around the earth it is eventually reflected by the sun so it is visible in our skies when we can't see the sun anymore.

#17 What does the moon do?

The moon doesn't appear to do anything at first glance, but when you get deeper into the issue you'll be surprised to find that it's actually vastly important to how the earth acts. If the moon was moved closer or further away from the earth it would affect the way the tides work and it could make sea levels rise dangerously and flood, or drop dramatically and cause floods in other places. It also links into how the ocean oxygenates itself and transports nutrients around the world, heat is carried mostly over sea on prevailing winds, so if the sea patterns changed climate would be greatly affected. It's a common misconception that the moon affects menstruation in women, but it's really just a coincidence that menstruation occurs every 28 days and the lunar cycle lasts this long.

#18 What's the circumference of the earth?

If you're measuring along the equator the earth has a circumference of 24,901.55 miles, but if you measure from the poles (ie, North pole to south pole) it's a bit smaller and has a circumference of 24,859.82 miles. This means that the earth isn't actually a perfect sphere at all and is in fact an ellipsoid, which is the oval version of a sphere. There is even a word invented to describe the unique shape of the earth and that is Geoid, which means 'earth like' and is basically a sphere that is just a little bit wider than it is taller.

#19 What's the dark side of the moon?

This sounds very mysterious, doesn't it? Sort of like a magical phenomenon. Astrologers certainly like to think of it this way and have all sorts of meanings for the dark side of the moon and what exactly it means, and they claim that people also have a lunar star sign as well as they star sign. In scientific terms, however, it simply refers to the part of the moon that isn't hit by the sun and is therefore not visible to us. If you were to walk on the moon the "dark side" of it would be like walking in pitch black, and it would also be absolutely freezing.

#20 What do you see in a solar eclipse?

A solar eclipse is an amazing visual spectacle where the moon appears to cover up the sun. Unfortunately most solar eclipses we see are only partial, but if you're ever around for a full solar eclipse it is absolutely stunning. Everything around you goes dark and it's almost like twilight. The sun is completely covered by a black disk and all you can see is a beautiful halo of light all the way around it- this is because the moon is smaller than the sun and therefore doesn't blot it out completely. Sadly the next total eclipse of the sun that will be visible in Europe is in 2015 on March 20th. However, if you're in America on November 13th 2012 there'll be one visible there.

#21 Why don't we constantly get hit by meteors?

Actually, we do get constantly hit by meteors. Every day earth is hit by thousands and thousands of meteorites from space, however most of these are as tiny as a grain of rice- or smaller! This means they're instantly burned up in the earth's atmosphere and we never notice anything different. The atmosphere is a protective barrier for us in this respect, however there are cases where meteors are big enough to break through. In 2009 one exploded over Africa and people could actually see it heading towards earth. In 1908 a meteorite struck central Siberia and the explosion was said to be as powerful as a nuclear bomb and caused horrific forest fires. However, these occurrences are thankfully very rare.

#22 What's the closest we've ever gotten to the sun?

In the 1980's NASA and a space company from West Germany got within 45 million km of the sun and were inside Mercury's orbit to do so. This was the Helios probe and in addition to being the closest vessel to the sun it was also the fastest at orbiting and was travelling at 70km per second. However, NASA are aiming to break this record with their probe in 2018 when they send a space craft up which they hope will enter the sun's atmosphere. They need to create a shield for the probe that can withstand the intense heat and radiation on the approach and I don't think that the probe will be manned in anyway except from earth.

#23 What would happen if you went out into space without a space suit?

Quite simply you would die, very very disgustingly and painfully. It's probably not very sensible to exit your spacecraft if you've left your space suit at home. Have you ever seen cartoons where the characters are in space and their head explodes when they go into space without a suit? Well, even though it wouldn't be that dramatic the cartoons weren't far wrong. Because of the pressure in space all the gases in your body would expand and bloat and eventually, yes, your body would as good as explode. The heat would cause your blood and any other fluid in your body to boil at an alarming speed and rate and the side of your body that was not facing the sun would freeze solid if you were in a certain distance. This would more than likely be instantaneous, however, so wouldn't be half as painful as it sounds as it would be over in seconds.

#24 where does the moon go during a new moon?

The moon doesn't "go" anywhere during a new moon, and the one a month phenomenon occurs when the moon lies directly between earth and the sun, so it is in direct conjunction with the sun. This means that the "dark side" of the moon is facing earth and to the naked eye it appears that the moon has completely disappeared. Rather than the moon moving somewhere else or disappearing it is simply a trick of the light that makes it appear as if it isn't there. However, with a sophisticated telescope you'd be able to see the faint outline of the moon.

#25 How long would it take to travel across the milky way?

The Milky Way is roughly 100,000 light years in diameter and 1000 light years thick. This means it would take you 100,000 years to get from one side to the other, however, by an interesting twist of reality it would feel instant to you. 100,000 would have passed, but because you'd be travelling at the speed of light- which is 186,000 miles a second- you'd be going so fast that time for you would stand still completely and when you finally stopped you'd have travelled the 100,000 light years in a snap of your fingers. However, this is all purely theoretical because a person couldn't go that fast without being liquefied by pressure.

#26 how long does it take for a falling star to hit earth?

This is really relative to the size of the star and the distance it's falling from. As you might know, the further something has to fall the more velocity it gains as it moves and usually the bigger impact it causes. This is why it's illegal to drop loose change off the top of the Eiffel tower. However, as the atmosphere in space is largely different to that one earth the speed differs greatly and factors like the heat of the star, if it hits any debris and how much it burns up in the atmosphere can all affect how it falls and at what speed. This means, of course, that we can't really give a figure. Though, technically a star is just made up of various burning gases, so if it fell the atmosphere would just evaporate the gas before it actually 'hit' earth. Plus, because of the speed of light, the star that you're seeing falling probably died a very long time ago.

#27 How hot is the sun?

This all depends on what part of the sun you're talking about, as the interior and the outside of it are vastly different, as is the collection of rays surrounding it. The centre of the sun is roughly 15,000,000 degrees Celsius, whereas the outer surface- known as the photosphere- is around 5,500 degrees. Sometimes there are magnetic anomalies in the surface of the photosphere that appear darker than the rest of the surface and these are in fact cooler and are around 4,000 degrees. The atmosphere that surrounds the sun is called the Chromosphere which is roughly 4,300 degrees in temperature, however this is a few thousand miles in thickness and the temperature varies depending on the altitude and the closeness to the sun, so it can reach temperatures of 1,000,000 degrees.

#28 Can we land on Mars?

At the moment we don't have the technology to actually land a human on Mars, but in 1997 the first Mars rover was sent up into space and landed on the surface of the planet, giving us photos of the planet and data about the composition of it. However, before this in 1973 Russia sent their Mars 6 craft up onto Mars, but communications were lost after just a few seconds. However, in 1976 America's Viking 1 ship landed on the planet and took thousands of photos and soil samples to analyse. However the Mars Rover was the first craft to actually move around on Mars and explore the planet.

#29 What jobs can I do related to astronomy?

Although most space fanatics dream of being an astronaut and flying into the deepest depths of space this is probably a very unrealistic goal and only a few people ever succeed into getting into this path. However, if you're truly passionate about astronomy, studying astrophysics at university and using this as a chance to gain experience and contacts in the industry can be a real gateway into the career. It all depends on what kind of path you want to follow, astronomical engineers build satellites and rockets, where as researchers and physicists are primarily theory based and help co-ordinate probes that collect data.

#30 How many earth years are 60,000 lightyears?

This is a common misconception that many people make, because the phrase light years sounds so much like it should be a measure of time. In actual fact a light year is a measure of distance and is based on how fast the light travels to the place. To put it very technically a light year is 9.461 × 1012 km, or 5.879 × 1012 mi. One light year is probably about 9.5 trillion km, so to work out 60,000 light years you're looking at maths that you can't even do on a basic calculator.

#31 What is a shooting star?

This is a misnomer and a shooting star is actually a meteorite shooting across the sky towards earth or simply across space. The glow that makes it look like a star is the effect of the atmosphere burning up the meteorite and because of this we automatically think that they're stars hurtling across the sky. Rather than being the size of rocks like they are in science fiction movies, most of these meteors that we see racing across the sky are actually the size of a grain and it's just the burning gas surrounding it that makes it look bigger.

#32 How long does it take for the sun's rays to reach earth?

Taking into account the speed of light and the distance the sun is from earth it take 8 minutes for the sun's light to reach us on earth, the same applies to all the other stars you can see in the sky. So, for a bit of a fun fact, the sun you're looking at now is actually the sun eight minutes ago. And the stars you're looking at tonight? They're what the stars looked light 8 minutes ago. Sometimes this can mean we're looking at stars that don't even exist anymore because they've burnt out, but we can still see their light because of the time it takes to come to us. It also means that if and when the sun explodes we won't know until 8 minutes after it has happened.

#33 What colour is a comet?

Generally the heat of a comet means that they appear a bright white colour in the sky. However, the tail of the comet can be a wide range of different bright colours that make comets really beautiful if you're lucky enough to see them. These colours are caused by different elements being burnt up in the comet's tail. For example, copper elements would make a green/blue tail, calcium makes it orange, and magnesium would make it electric white. This sort of technology is copied in fireworks with metal salts burnt to create colours in the same way a comet tail does.

#34 How do we know how old the earth is?

Through a complex system of carbon dating and radiometric dating we can determine the age of rocks and composites on the earth so that we can calculate the age of the earth from this. Although we can't get it 100% accurate and give the earth a birth date. In Radiometric dating the researchers look for uranium in rocks and date it with equipment in the labs, because of the mixture of gases and substances that we predict were formed first when the earth was created, and the fact that uranium is a non renewable source (ie, we can't create it, it's just there) we can confidently say that if we date the uranium from the rocks we can date the earth as well. Thanks to scientists doing this we can quote the earth as being roughly 4.54 billion years old. Try fitting the candles on that cake!

#35 How do you recover a satellite?

A satellite is a small, unmanned ship that is sent up into space and used to monitor the conditions in space or around a certain planet. These satellites can be programmed to orbit a certain planet or moon and will then send pictures or video feed back down to earth. As for getting them back, well that's the tricky part. You see, when you launch a satellite you need to do it at just the right speed to get it to orbit the thing you want it to, for example, around the earth. If you push too much it will leave the earth's gravitational pull and you'll never see it again, and if you do it right it will constantly stay in an orbit around a certain point. This means it won't actually come back to earth. Some sophisticated shuttles that use satellite technology are manned by people and are brought back to earth the same was as a shuttle or rocket is, but a standard satellite will stay in orbit forever, or until it gets knocked by flying rock or something which would then knock it back to earth. 70% of the planet is water, so there's a 70% chance that when the satellite drops from the sky it will land in the sea. Otherwise, it will break up into small pieces as it falls and hopefully the atmosphere would break it up. Though, experts say the chances of it hitting a populated area are very slim.

#36 What is the double dark theory?

This is a pretty complex theory which assumes the existence of Dark Matter. Dark matter is an experimental concept which refers to the dark, uncharted parts of the universe. Double dark theory deals with the distances between the visible universe, which they estimate covers roughly half of the universe, and the dark section of the universe. Double dark theory uses this to predict things like the big bang and also to predict the existence of other galaxies and chart their supposed position and size in the overall universe.

#37 How hot are stars compared to the sun?

This links back to the different kinds of stars that are in our universe and deals with the different kinds of stars and their categories. The sun is a G type star and is roughly 9400 degrees Fahrenheit and a lot of stars are actually hotter than this. A good rule to go by is the whiter the colour of the star, the hotter it will be. The sun is a yellow-orange colour and is therefore a lot cooler than most of the white and bluish coloured stars we see in the sky. A star can be anything as hot as 70,000 degrees which is almost seven times hotter than the sun!

#38 When did the big bang happen?

There are many different theories about this question, and as such it is widely open to debate. We can't ever hope to accurately put an age on the earth as our technology is ever evolving and giving us different estimations and figures all the time. Plus, factors we haven't taken into account before are constantly coming up and putting a whole new spin on the theory. Carbon dating predicts that the earth is around 5 billion years old, though some theories push this prediction up to 13.7 billion years.

#39 What would happen if a meteorite hit you? Would it burn?

This really depends on the size of the meteorite and where it hits you. There are several account of people being hit by meteors and in 1954 a woman was laying on her sofa when a meteor crashed through the roof and hit her on the side. She lived, but suffered terrible bruising and minor internal injuries. She wasn't burnt as such, but the area that was hit was pretty badly affected and cut. This might have been due to the fact she was indoors and the meteor had travelled through the roof and top floor before it got to her and had cooled down. However, there are stories of people being stood outside when one hit and being killed instantly or severely burnt. In fact, about 65 million years ago a huge meteor hit earth and caused mass extinction of the dinosaurs if you ask some people's opinion, so the effects can be very varied!

#40 Where do we find wormholes?

Wormholes are technically a science fiction myth, so the answer is, we find them in science fiction books and movies. Though, if worm holes did exist they would be a collection of black holes linked together, and we know that black holes exist. Black holes can be found anywhere at all in space, usually near a collection of old stars that are ready to burn out. We're not exactly sure what causes them and why they're there, but they can be found anywhere at all in space. However, if you found a black hole you wouldn't have time to congratulate yourself or take a photograph.

#41 How far away from us is the moon? Is it closer than the sun?

From earth if you were to go direct to the moon it would be 240,000 miles away which is quite close when you think about it in terms of the vastness of space. This is why we can see so much detail on the moon on clear nights. The sun, on the other hand, is 93 million miles away from earth so the moon is most definitely close to us than the sun is. It's also a lot easier to get to and land on than the sun is.

#42 What does the sun do apart from cause light?

The sun does, of course, provide us with the light we use to see and move around in, but in actual fact it does so much more than that. If we didn't have the sun we wouldn't be able to breathe. This is because the plants on earth use the sun's light in photosynthesis which then turns the carbon dioxide in the air into the oxygen that we breathe. The sun also provides vital heat that we need to survive. If the sun were to explode or be blocked out for a long period of time, the entire earth would fall into another ice age and life on earth would effectively be over.

#43 Why isn't Pluto a planet anymore?

We've always known that Pluto was the smallest planet, and in 2006 it was discovered that it was actually a lot smaller than it had first been thought. They also discovered some interesting things about the way it orbits. A planet typically maintains the same orbital path and they are kept in a set region around the sun, however scientists found that Pluto actually orbits above and below this set disk frequently. Pluto has a 248 year orbital period, and for 20 of these years it is closer to the sun than Neptune is. In 1992 a small planet like body which was named Quaoar was discovered in a region called the Kuiper belt and it's orbital pattern was found to be more planet-like than Pluto's was. Later the body Eris was found in this region and it was also larger than Pluto and more inclined to orbit smoothly. This created discussions other whether or not Eris was a planet or not, and eventually it was decided that what defined a planet was if it was large enough that it's gravity could clear out it's region in space. Hence, Pluto became a dwarf planet along with Eris and all other undiscovered planet-like bodies.

#44 Which planet has the most moons?

Jupiter currently has the most moons of the eight planets in our solar system [see previous question for explanation of why Pluto is no longer part of this] and currently this planet has 63 moons, most of which are named though some of the newly discovered ones have not been classified. In a close second is Saturn with 61 moons and Uranus with 27, then Neptune with 13. These four planets are special because every year new moons are being discovered around them. Mercury and Venus are unlucky in the fact that they don't have any moons, and Earth of course just has the one. Interestingly enough the Dwarf planet, Pluto, had three moons called Charon, Hydra and Nix whilst Mars, which is considerably bigger, only has two.

#45 What would happen if the earth fell into a black hole?

It's safe to say that if we were pulled into a black hole we would die, because the complex lack of pressure and the distortion of it would rip the earth to pieces in under a second. Theories about what would happen if a black hole came near earth are that we'd experience massive earthquakes and tidal waves and volcanic eruptions all over the world as the planet started to get disrupted and then suddenly we'd be sucked into oblivion. Some say we'd have a few days warning if we were approaching a black hole, whereas others say it would be so instant we'd not even realise it was going to happen.

#46 Who discovered black holes? Didn't they die discovering it?

Technically no one discovered black holes. It's not like discovering gold or inventing the wheel. In 1916, Karl Schwarzchild used Einstein's theory of relativity to calculate what would happen if something like a star was concentrated down to the smallest possible size. He doubted this could happen, but he said if it did the gravity of the other planets around it would not be affected. Many of his theories have now been disproved, and it was John Wheeler in 1968 who coined the term Black Hole and contributed a lot of research to the field.

#47 What planet has the shortest year?

For purpose of answering this question, we'll measure everything in relation to an earth year, using the 24 hours in a day system used on earth to define days. Mercury has the shortest year, at just 88 earth days long. This is because it is the closest planet to the sun and therefore takes less time to complete it's full orbit. A year on a planet is how long it takes that planet to complete a full circuit of the sun and return to the same point, so it takes Mercury 88 days to do this. Neptune has the longest year and it takes 164.8 earth years for it to orbit the sun completely which shows you just how far out into the solar system it really is in relation to us seen as we only take 365 days to orbit the sun.

#48 If you were in space, what could you see on earth?

It's a long standing space myth that you can only see the Great Wall of China from space, but you can in fact see a lot of other things. Astronauts have reported being able to see the Pyramids of Giza in Egypt from space when they used binoculars and Ed Lu, a popular astronaut and head of the Expedition Seven said that he could see roads and highways when he was in space and even the flashes of sunlight bouncing off the shiny outside of aeroplanes! In regards to the Great Wall he revealed that it's actually a lot hard to see than other things are from space and you have to know just where to look. This is all based on the average earth orbit height of 135 miles high.

#49 How do we know the earth orbits the sun? Couldn't it be the other way round?

To us it definitely looks like the sun is moving around us instead of us moving around it. After all, we can't feel the earth moving, can we? And the sun does appear to move across the sky. The early scientists certainly thought this and were adamant that the sun revolved around the earth. However, modern science has effectively proven that the earth does move around the sun because the centre of gravity in our solar system is much closer to the sun than it is the earth and the earth is moving around the centre of gravity- as is everything else in the universe. Although you can't feel it moving, remember what it feels like to be in a car. You can't feel it moving, but you see the evidence of it outside. Just imagine the earth is a car driving around the sun.

#50 What is a blue moon?

It's a popular saying "once in a blue moon", isn't it? Usually used by the older generation to talk about things that very rarely happen. However, blue moons actually aren't that rare at all! A lunar cycle is made up of 28 days, and because of this we usually have 12 full moons a year. However, not every month is 28 days so this leaves us with left over days and every so often we have enough days built up to create an extra moon- meaning, one season of the year has four full moons rather than three. The third moon in this four moon cycle is referred to as a blue moon and we have them every one or two years.