secret codes

Why Do People Need Secret Codes?

Imagine you have a secret you want to tell your best friend, but nobody else. Perhaps last night you discovered you could fly. If everyone found out they would ask you lots of boring questions like, “What does my house look like from the sky?”, and your Dad would want your help cleaning out the gutters of the house. Yuk. Stuff like that.

If you were alone with your best friend in the same room then sharing the secret would be easy to do, but if he or she was somewhere else, or you were not alone, that would be more tricky. Somehow you would need to send the secret to that person in a way that only they could understand it. How could you do that?

You could make up your own special language that only the two of you could understand, but creating a brand new language would be very hard work and would take up a lot of time and practice; years probably. All that effort just in case one day you need to share a secret. That’s quite extreme.

How Secret Codes Work

A simpler way would be to use your normal language, but wrap up the message in a secret code. That would be a bit like sending a letter in a locked envelope. If you gave your best friend, and only your best friend, the key to unlock the envelope before you sent the message, then only he or she would be able to open it and know its true meaning. This is how all secret codes work.

I’m going to teach you a few new words. A secret code can also be called a cipher. Its pronounced ‘si-fer’. The original message in your language is called the plaintext. The message written in secret code is called the ciphertext. The act of turning a message into the coded message is called encryption; you encrypt the message. The act of turning the coded message back into the normal message is called decryption; you decrypt the coded message. The exact way encryption and decryption works is called the key for that particular code.

An Example: The Caesar Cipher

The best way to explain how this works is to show you. Let’s use a real secret code that was used a long time ago. It’s called the Caesar cipher, and is named after the famous Roman general, Julius Caesar, who used this way of encrypting his important letters, such as commands to his soldiers on the battlefield, so that his enemy wouldn’t understand them if they found them.

Let’s imagine that you want to send your friend the message “I can fly.”. The way this particular cipher works is that it swaps each letter in the message to a different letter in the alphabet to make it look like nonsense. The Caesar cipher transforms each letter into the letter 3 places further up the alphabet. They key to this code is +3. Other types of cipher transform letters in different ways to do the same thing. Our plaintext message is icanfly when written with no spaces inbetween. Now let’s encrypt the message. The table below shows how that transformation works for each letter of the alphabet using the Caesar cipher:

After encryption the message reads “MFDQIOB”.  That doesn’t mean anything to most people, does it? But to your friend, who knows what you have done, it does. When they receive the message they know they need to do the opposite transformation to be able to read it. In this case, they will need to change each letter in the ciphertext to the letter 3 places before it in the alphabet and then put the gaps back in sensible places so that the message makes sense:

So your friend will turn MFDQIOB into icanfly and then understand that you have cracked the ability to fly.

There are lots of ways of turning plaintext into ciphertext and back again. The history of secret codes is interesting on its own, but one of the most wonderful things about it is that nearly 80 years ago some British people who were trying to break some secret codes that they didn’t have the keys for created the World’s first computers to help them. I’ll tell you more about that in my next blog post.

EBHEBH

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stars

The stars on a clear night look as if each are the same distance away from us. Some appear bright and big, and some small and dim. It looks like a curved picture has been hung up across the sky. Because we are small creatures living on a little rocky planet that circles around a normal sized star we don’t find it easy to understand how big the Universe really is. Really, the night sky is our view of the Universe, and it has incredible depth. Some stars are close and some are very far away, and they can be very different sizes and brightnesses.

At this time of year an easy-to-see constellation is high in the sky just after the sun sets. It is called Orion, sometimes known as Orion the Hunter, and if you look at the picture at the top of this post you might see why. You have to use your imagination a bit - you do to see any of the pictures people say you can see in the night sky - but it can look a bit like a someone holding a bow with their other arm raised high behind as if pulling the bowstring or holding a club. There are three equally bright stars in the middle that might be the hunter’s belt.

A little bit down and to the left of this group of stars is a very bright star that you should see easily unless there is a cloud or a tree or a building in the way. This star is called Sirius and the ancient Egyptians used to think it very important because, when it rose on a certain summer morning after being behind the Sun for 70 days, it meant that the river Nile was about to flood and water the desert. We still think it important for a more simple reason; it is the brightest star in the sky.

Both the Orion group of stars and bright Sirius are almost directly south of wherever you are, if you look for them between 7pm and 9pm in the evening at this time of year, so I thought now would be a good time to point them out to you. I hope you get a clear sky one evening this month so you can see them for yourself before bedtime.

Among these beautiful lights there are some giant stars. Which do you think is the biggest star in this part of the sky? If I didn’t know better I would say Sirius, because it is the brightest, and if all stars were the same distance away from us that would be true but they aren’t.

Sirius is eight and a half light years away from us. That is a distance that the human brain can’t really imagine: how far a torch beam would have traveled eight and a half years after it left the torch. Even so, this is one of our Sun’s neighbours; the seventh closest star. It is bigger and brighter than our Sun. If we could swap them around and make Sirius our Sun it would be about 26 times as bright. This is because it is bigger in size, and also because it is burning hotter: so it sends out more light. But in this part of the night sky there are even bigger and brighter stars than this.

There is a star to the right side and above Orion’s bow. It belongs to a neighbouring constellation, Taurus the Bull. Our hunter is chasing this bull. If you spend some time looking at the sky you may notice that this star looks a bit red rather than white or blue. It is a giant red star called Aldebaran and is about 67 light years away; so nearly eight times further away than Sirius. Although it doesn’t look as bright as Sirius it is 16 times brighter and much bigger. Let me explain what I mean by that. If you hold a small torch close to your eye it will be brighter than the lightbulb hanging from the ceiling but only because it is closer to your eye. Sirius appears brighter than Aldebaran for the same reason. If you were able to fly close to huge Aldebaran the red light would be as bright as 425 suns, but it is not the brightest star out there in that part of the sky.

The bright white-blue star at the foot of Orion is called Rigel. It is twice as far away as Aldebaran - 860 light years - but still appears just as bright. It is a huge blue giant and as bright as 85,000 suns if you could get close enough to see for yourself! Just as bright as this but a bit closer at 560 light years away is the red giant Betelguese. It is the same distance above and to the left of the three belt stars of Orion as Rigel is below and to the right. If your eyes get used to the dark you may be able to see the difference in colour between red Betelguese and blue Rigel. Huge and amazing though these giant stars are, they are not the brightest in Orion.

The three lovely belt stars are easy to find in a clear sky but they aren’t the brightest to our eyes. The middle of the three, Alnilam, is twice as far away as Rigel - 1340 light years - and if you could get close enough you would see that it is as bright as 375,000 suns. It is a blue supergiant, which is a pretty good name for a star that is 20 times the size as our Sun and five times hotter.
I hope I haven’t clouded your head with numbers. If you can turn these numbers into a picture you will start to see how three-dimensional the night sky truly is and how stars aren’t necessarily like their neighbours.

Here is a drawing I have made to show you how far away these five stars are from us compared to each other:

I’ve also made another drawing to show you how big they are compared to each other:

A few weeks ago I found this old but good video on YouTube about the sizes of things in space. Some of the giants I have shown you are in it and some even bigger ones too. I hope this helps you imagine how big the Sun, Sirius, Rigel and Aldebaran are compared to each other:

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stars

Source: Image courtesy K. Churyumov

The photo above was taken by Klim Churyumov on 21st September 1969 using a big telescope in Kazakstan whilst on a comet hunting expedition with one of his researchers, Svetlana Gerasimenko. It is of course our friend comet 67/P Churyumov-Gerasimenko and this was our first glimpse of it when it was discovered by these two astronomers. They had no idea of course that 45 years later we would be sending a robot spacecraft to orbit and then land on it.

The European Space Agency have funded a short film that explores how important the Rosetta mission might be to us, the human race, in the future. It is a bit dramatic for my personal taste, but still good. Watch it on a big screen with the volume up if you can and press the enlarge button on the video controls at the bottom right of the video below:



So far, Rosetta has been an amazing success. Just like the guy says in the film, all sorts of things could have gone wrong before it arrived at the comet but amazingly they haven’t. It isn’t just about what we have learnt already and what we might learn over the next year whilst the mission continues. It is also about the fact that we’ve had the ambition and bravery to actually do something so difficult and get this far.

Anonymous 1 Comments

fossils

How old is our planet, Earth? It’s old. Really old. Mind-staggeringly, head-hurtingly old. In a minute I will give you one useful number that will help you understand how old and how all the rest of history fits into the picture.

Before I do that lets talk about big numbers. What is the biggest number you can imagine? I can imagine 10 things with no problem at all. 100. Yep, easy. 1000? There were nearly 1000 people at my senior school so I can think of that number. How about 100 schools like that put together, so 100 000? Its possible to think of that. Ten of those is 1 000 000 - one million. I stop there. That is about the limit of what I can imagine but that is good enough for now.

So imagine those numbers in terms of years. I don’t know about you, but for me that is a bit harder. I’ve lived for 41 years so even 100 years is a long time. 1000 years ago we know our country was in Saxon times just before the Normans invaded in 1066. 10 000 years ago we are beyond written human history so we don’t have stories from those times about what people were doing then. 1 million years seems like an incredibly long time to think of, doesn’t it?

Well our magic number is four thousand five hundred and forty. 4540. Because the Earth is around 4540 of those 1 million years old! But 4540 is a simple number and it will be very helpful to remember when later on we talk about fossils and dinosaurs and such like.

The picture at the top of this post shows how some people talk about time in the Earth’s long lifetime. These four really long periods of time are called eons. There are other ways of describing the Earth’s many ages and we will talk about them another time. The start and end of these ages can be said to have happened so many millions of years ago, which can be written MYA. So for example the beginning of the Phanezoic eon, the eon we are living in now, began 542 million years ago or 542MYA. This is the age where the first plant and animal fossils were found - before that there were probably only tiny microscopic bacteria and viruses that lived on our planet. You’ll see from the picture that plants and animals came quite late on the scene in Earth’s lifetime.

How do we know how old the Earth is? There are a number of different ways we know but I’ll tell you one way that you’ll understand if you’ve read my other posts about what stuff is made of. There is a type of metal in some of the rocks in the Earth called Uranium. Like all materials it is made of lego-brick like atoms. Uranium atoms are a bit unstable, but only a bit. From time to time one atom will suddenly change into another one - a lead atom. Lead is a metal too and in very old houses water pipes used to be made of it. Actually it changes into a misfit isotope lead atom not a regular normal one. It doesn’t happen very often. In fact if you took a lump of uranium of any size it would take 700 million years for half of the atoms in that lump to turn to lead. By measuring how much misfit lead isotope is in meteorites and moon rock - which we think were made at the same time as the Earth - then we can work backwards and know when that rock was made. So far all the rocks we have tested point to a number about 4500 million years.

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stars

Image courtesy of ESA

In my rush to tell you all about the Rosetta mission and update you on it’s progress I forgot to tell you why the European Space Agency (ESA) are chasing a comet in the first place.

Comets are special because they were made at the same time that the other parts of the solar system were made - the Sun and the planets - but since that time, out in deep space, nothing much has happened to them. Our comet 67/P has been circling the Sun far far away in the Oort cloud until some time ago something bumped it and then it fell towards the Sun ending up travelling in a much shorter elliptical loop where we first noticed it in 1969. Despite the change in path, it is still the same lump of rock and ice that it always was since the beginning of the solar system. What is it made of? That is the question that Rosetta and Philae are going to find out. It is the first time we’ve had the chance to land on the surface of one of these ancient bits of our solar system and touch it and smell it. Up until now we’ve only seen comets from Earth or from shorter a distance away from a space mission. Never before have we been this close.

There are eleven measuring machines on the main Rosetta orbiter spacecraft and ten on Philae, the lander. Each of them was built by different teams of people in Europe and the information from each will go back to these same teams during the mission. Have a look at the ESA web page here to see what each of them does.

There is also a question that the Rosetta mission may help to answer; where did the water on Earth come from? A long way back near the beginning of the solar system lots of big rocks and chunks of ice that later became planets, asteroids and comets flew around bashing into each other. Where do you think the craters on the Moon came from? Probably most of the big ones were created around this time called the Late Heavy Bombardment. No one is quite sure why it took place but we have good evidence it really happened. Some people think that a lot of the water on our planet also arrived around this time from icy comets hitting the Earth. How could we ever know if that is really true? How about landing on an ancient comet now and finding out what type of water is in it?

OK that sounds an odd thing to say. What do I mean what type of water? Well, water, like all things, as we know from earlier blog posts, is made of lego brick-like atoms. What I haven’t said before is that water has misfit atoms in a very small number of molecules. Think of them as lego bricks that are the wrong colour for their normal type. We call these misfit molecules isotopes. Water has two different types of misfit. We know how common they are in our water on Earth - have a look at the picture above - but we also know that they can be present in different amounts in water from other parts of the solar system. So that is what I mean by type of water - the amount of isotopes give water from different sources their own different fingerprint, if you want to call it that. If the water on comet 67/P has the same proportion of misfit isotopes that would be another clue to suggest that our water on Earth originally came from comets crashing into it. If it does not, that’s not a problem, it helps us to look in other places for where it might have come from instead. Our water may have come from asteroids in the past, from the rocks that made up the early Earth, or from early plants or bacteria living much before the dinosaurs.

So as well as being an amazing thing to do in and of itself, landing on this comet may also give us another clue as to where our own water originally came from.

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stars

Source: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Since I wrote to you about the Rosetta space mission a few things have happened that I wanted to tell you about. When I first mentioned the comet to you in August, the spacecraft was about 100km away from comet 67/P - the same distance from Luton to Coventry - but now, a few weeks later, it is only 10km away. It is exactly on schedule as was planned when it blasted off from Earth ten and a half years ago.

In less than 3 weeks the small robot landing craft, called Philae, will set off from the main Rosetta spaceship and land on the surface of the comet - the first time that the human race has ever attempted to do this. We have only just properly seen the comet after Rosetta got close enough to start taking good photos of it and so up until now the people at the European Space Agency (ESA) who are running the mission weren’t sure where the lander was going to touch down. For the past few weeks they have been looking at the surface of the comet to try to find a place that is both a good spot to land safely but also interesting enough to bother going there at all and now they have, a place called site J.

You will remember that comet 67/P is a funny shape - a bit like a rubber duck. Site J is on the ‘head’ of the two lumps of the comet. If Site J doesn’t work out during the landing then ESA have a back up landing site called Site C on the other lump, the ‘body’ of the rubber duck. The photo at the top of the blog shows where site J is on the comet and the photo below this paragraph shows a close up of it taken when Rosetta was 30km away from it a few days ago. Click on it to make it nice and big.

Source: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Of course Site J is a bit of a dull name for a place that is going to make history and so ESA have started a competition for people to give the place a better and more interesting name. Want to have a go? Then follow this link and send them your suggestion.  You have a few more days before the competition closes on 22nd October.

By the way, as you know, I normally try to create the photos and drawings I use on my blog posts myself. When I’m talking about a comet deep in space that is of course very hard to do but instead I’ve used photos that ESA have been taking using the cameras on Rosetta and then putting on their website, www.esa.int. I’ve used the full sized images they have published so make sure you click on all of them to see them in greater detail. Remember, these are not works of art or imaginary drawings made up by special effects people, they are photos of a real space object that has come from far outside our solar system. If you have a moment go and have a look at more fantastic photos on their website. Here is a photo Rosetta took of itself, with the comet in the background, a few days ago:

Source: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Philae will land on the comet on 12th November. I’ll try to remember to give you another news report around then.

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science

A few weeks ago I wrote to you about how everything was made of tiny little lego-brick-like atoms. Later, I wrote about how some things, like gold and diamonds, are made up of the same type of atom-brick. But like most toys made from of lego bricks, most things in reality are made up of many different types of atom joined together not just one type.

Like lego, atoms can be made to join with other atoms to make bigger and more complicated shaped bricks. These bigger bricks are known as molecules. It is this fact that makes the world around us full of very different types of stuff. Although the whole universe, that we know of so far, is made up of just 98 types of atom you can build very different types of things by joining them together in different ways and different arrangements. It is worth saying that although they are bigger than atoms, molecules are still very very small things indeed. Even the big complicated ones.

The above picture shows six lego brick molecules that I made up in my head using just four types of lego brick. It didn’t take me very long to do. Have a go yourself if you have some lego or other building blocks at home. Make some models of molecules and see how easy it is to come up with new shapes using only a few types of brick.

A good example of a very simple and small molecule is water. It is made of one type of atom brick joined up with two types of another. One drop of water contains huge numbers of these molecules rubbing against and sliding around each other. It just so happens that this combination and arrangement of atom bricks makes stuff that is wet in warm weather but frozen solid when it’s cold and that can turn into vapour when it gets very hot, such as in a kettle.

For an example of a much more complicated molecule that contains lots of different types of atom bricks you need look no further than your own hair and finger nails. Much of these parts of you is built from molecules of something called keratin. One molecule of keratin is made of more than 4000 atoms stuck together in a long spiral shape. These molecules stick to each other to make very long, strong chains. If water is just like three Lego bricks of two different types joined together then this molecule is like the Lego Star Wars Death Star - made of lots of bricks of lots of different types. The Death Star model has 3803 bricks to be exact so a keratin molecule has even more parts than that. Even so, it is still very small because atoms are incredibly tiny things indeed.

Because they are all sorts of shapes and sizes each type of molecule acts differently to others. This is why millions of water molecules together in a glass of water are see-through and liquid but lots of keratin molecules create tough bendy stuff like your nails.

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stars

We all know that out in space things go around other things. They circle round and round. Our planet, the Earth, goes around the Sun. Our Moon travels around us. The moons of Jupiter orbit around it and Jupiter itself rotates around the Sun just like we do.

The words we use to describe this movement are a bit misleading. They can make you think that things travel around other things in perfect circles. Around. Round. Orbit. Circle. The fact that the planets and our Sun are sphere-shaped also gets us into the same mindset. So let me tell you something that might surprise you; the planets in our solar system don’t go around the Sun in circles like the drawing at the top of this post. They follow a different shaped path shown in the drawing below:

The shape of these paths are called ellipses. An ellipse is like an oval shape. In space, things go around other things in elliptical orbits not circular orbits. There are a few important things to say about this. Let’s use the Sun and the Earth as an example but the same rules apply to all things in orbit around other things.

Firstly, the Sun is not in the centre of the ellipse. It’s over to one side. If we think of us on the Earth going around the Sun once every year this means that we are at different distances to the Sun depending upon where we are on that path. Because the path is so big and the ellipse is nearly circular we don’t noticeably see the Sun getting bigger or smaller in the sky. However, there are times the Moon is a little bit closer or further away on its elliptical orbit around us and it is possible to measure the difference in size. You may have heard some people get carried away and talk about a ‘super moon’ on nights when the Moon is full and also closest to the Earth - but take it from me, it isn’t very noticeable.

Secondly, the shape of the ellipse can be different. It can be very long and narrow or almost circular. Comets have very long narrow paths, whereas most of the planets have nearly circular ellipses. The long narrow elliptical paths have their centre very far to one side, whereas the circular ones have it almost in the middle. This is why comets come from so far away out in space and go so close around the Sun, sometimes close enough to burn up completely.

Thirdly, the reason for the elliptical shape is gravity. The Sun is heavier and is pulling the Earth towards it. Because the Earth has speed of its own in another direction it doesn’t simply get pulled into the Sun, but these two forces cause the elliptical orbit that it travels upon. This also means that the speed of travel is not the same all the time. Half the time during the orbit our Earth is falling towards the Sun and is speeding up, whereas, after it has passed it at the closest distance it ever gets to it, it flies away from the Sun and starts to slow down. The second half of Earth’s orbit is spent slowing down until it reaches the most distant point away from the Sun when it begins the cycle again speeding up and falling towards it.

So how fast does the Earth travel around the Sun? It depends upon what day you ask and where in it’s orbit it happens to be. It is closest to the Sun (and fastest) around 3rd January each year and furthest away (and so slowest) around 4th July. Instead people give the simple answer as an average of all those possible speeds, which is just under 30 kilometres every second or 66 000 miles per hour. If it helps, thats fast enough to get to the Moon in 3 and half hours! But remember because the Earth travels on an ellipse not a circle half of the days of the year we go faster than that and half of the year we go slower.

The last thing to say is that with elliptical paths you can see that it is much easier for two or more orbits to cross one another, increasing the chance of space objects bumping into each other at high speeds. This makes for a much more exciting Universe and explains why, everywhere we look around the Solar System, things have and still are bumping into other things. Next time you look at the craters on the Moon think about how they got there.

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Anonymous 2 Comments