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.

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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.

If you would like to listen to this blog post instead (apologies for the sore throat, by the way) then press play on the audioboom widget below:

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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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stars

Catching Up With A Comet

Photo by ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Ten years ago the European Space Agency launched a rocket into the sky. It whizzed around the sun a few times, speeding up as it went, and then around a few planets, including the Earth three times, on a cleverly planned path to hit a very small target a long way away. Clever is not really a big enough word - you try throwing something at target so far away that it won’t hit it until ten years later! The spacecraft at the top of this rocket is called Rosetta.

At the beginning of this month, August 2014, Rosetta reached its target, a comet speeding its way towards our Sun that at the moment is somewhere between the orbits of Mars and Jupiter. This comet has the rather long and difficult name of 67/P Churyumov-Gerasimenko, because of the two people who discovered it. For the sake of the rest of this blog post, and mostly because I can’t pronounce it properly, let’s just call it comet 67/P. Here is a map of Rosetta’s journey:

Source: ESA

Comets are big dirty snowballs of ice and rock that sometimes come from very far out in space and loop around the sun. We think there are countless numbers of them surrounding our solar system in a dark region of space far away from the light of our star called the Oort Cloud, where they have been for a very long time not doing very much. Comets are different from asteroids - asteroids are made mostly of rock and are only found inside our solar system. Sometimes something, maybe a bump with a neighbour, causes a comet to fall in towards the Sun from the Oort cloud and it begins a long journey slowly picking up speed - it can take millions of years until it reaches the inner solar system. Three or four of these long-period comets fall in towards us like this each year. When they arrive they sometimes loop around the Sun and whizz off again never to return, sometimes they get too close and burn up and sometimes they get ‘captured’ by the Sun’s gravity and start to make much smaller circles inside the solar system where we can see them buzzing past us at regular intervals thereafter - we call these ones short-period comets.

This comet, 67/P, is a short-period comet that goes around the Sun every six and a half years or so and is about 3 kilometres by 5 kilometres in size. Since it was discovered it has been around the sun seven times. It isn’t a perfect sphere as you might imagine it should be. Far from it, as you can see from the photo at the beginning of this post, it is an odd shape.

Of course you already know that comets are things that sometimes are bright enough to be seen in the night sky and they have long tails behind them. So where is the tail on this one? The tails are caused when comets get closer to the sun and some of the ice begins to melt. Comet 67/P is on its way toward the sun right now and it is going to be Rosetta’s job to follow it closely for the next 18 months and watch what happens to it as it starts to melt and its tail begins to grow. In fact it is already starting to melt as this next photo shows:

Photo by ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Unfortunately, like most comets, 67/P isn’t close enough or big enough to be so bright that we can see it from Earth with our own eyes, although it can be seen with a telescope. But you don’t need a telescope. The cameras on Rosetta are sending back the most incredible pictures we have ever seen of a comet close up.

This event is important because this is the closest we have ever been to a comet before. The Rosetta spacecraft is less than 100 kilometres from the comet right now and soon will be about 30 kilometres away. In November, it is going to launch a small landing craft, called Philae, onto the surface of the comet. We’ve never tried anything like this before. We’ve seen plenty of comets in telescopes but have never touched one until now.

Knowing more about comets is important because we think they are very old - as old as our Sun and the planets spinning around it. Learning more about comets may mean we learn more about how our solar system was created 4500 million years ago. When Rosetta finds out some more interesting things I’ll let you know.

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stars

Seeing the stars is a hard thing to do when you are young. This is one of the reasons why I want to tell you some useful things about stars on this blog - so that when you do get the chance to see them with your own eyes you are able to look for the things that are interesting. When you are young every minute of star-gazing time is precious.

I’m writing this in July. In the UK, where I live, it is summertime. This should be a good time for seeing the stars because the skies are often less cloudy and it is normally nice and warm outside. The evenings are warm but they are also light, which is where the problem begins. That big star very close to our planet that we call the Sun is still in the sky or has only just gone down under the horizon and the sky is still too bright to see any stars. They are there, of course. They are there all day but imagine trying to see a small candle flame at the end of the road when someone is shining a powerful torch up close in your face - you just won’t see that candle.

This time of year most children go to bed when it is still light outside. Or should do. By the time the stars are properly out and nice and bright it is nearly midnight! That is no good at all even for many grown-ups. Things are different in winter in the UK. Nights are much longer and around Christmas time it can be dark by four o’clock in the afternoon and it will stay that way until nearly eight o’clock in the morning. That gives us 16 hours of darkness where we might be able to see the stars! That sounds much better, doesn’t it? But it is winter and it is more likely that there will be bad weather and clouds in the way that block out the stars. If there aren’t it is quite likely that the sky will be beautifully clear and full of stars but it will also be very cold outdoors and after a short while you’ll want to go back inside and warm up.

When it is warm outdoors in summer, the sky is light in the evening. When the sky is dark in the evening in winter, it is often also very cold. So you see it really is not easy to watch the stars with your own eyes when you are young living here in Britain. I have been thinking about this problem and I have some ideas about how to get outdoors and see the night sky. Here are my ideas:

Idea 1 - If the weather forecast says the sky is going to be clear one night in Spring (February to April) or Autumn (September to November) that might be the time to go outdoors when the sky gets dark earlier than the summer but it is still warmer than in winter.

Idea 2 -  It is difficult to see most stars on warm, light summer evenings but it is sometimes possible to see planets. Mercury and Venus can sometimes be seen in the sky shortly after the sun goes down and when they are there they are usually very bright. Sometimes Mars and Jupiter are also in the sky at this time of year and can be seen earlier in the evening twilight before the stars come out. It is best to look at a star chart on a phone application or on the internet before you go out to know if there are any planets up that evening and where in the sky they will be.

Idea 3 - The same is true for the Moon in summer. It will be in different parts of the sky at different times of the month but there will be one week every month when the Moon will be in the sky and easily seen during the early evening, if the weather lets you.

Idea 4 - On a cold clear winter evening wrap up really warm and go outside for just ten minutes and see how many stars you can see. Don’t worry about looking for anything in particular. Just stand underneath them and enjoy the view. Then keep that memory safe. Whenever you see a photo of stars you can remember that you stood under the same stars yourself. Even just ten minutes of sky-watching is better than no minutes.

Idea 5 - Keep reading my blog posts about stars as and when I post new ones on this web site. When you are able to get out next and see real stars you may be able to find some that I’ve been talking about and know some more about them.

There is nothing like seeing the stars for yourself in real life, rather than hearing people talking about them, or seeing pictures of them on television or in a picture.

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stars

Arcturus peering through the clouds at night | Image copyright Graham Jarvis 2014, all rights reserved

Today I’m going to tell you about a star. Just one. Its not a particularly special star but there is a very good reason that I am going to talk to you about this star first, of all the many many stars in the sky. It is because it is easy to find. If we are going to to talk about stars in the night sky together I want to you to be able to look up and see what I am seeing. Even if you don’t know much about stars, I think I will be able to teach you how to find this one.

The name of this star is Arcturus. Funny name, isn’t it? All stars have names given to them by people who watch stars for a living but some stars have nick-names that are often very old. Arcturus means something like “bear-watcher”, in the Greek language. Why would a star watch a bear? Well it goes back to the days before television and street lights, when people had little to do in the evening but look up at the stars on clear nights. They imagined they could join the stars with lines (like a dot-to-dot puzzle) and draw shapes with them. Its the same as when you see a cloud in the sky that looks like something familiar. One shape high up in the sky they thought looked like a big bear. It also was in the northern part of the sky and north was the direction that Greek-speaking people knew bears lived. The star we are talking about, Arcturus, isn’t part of this dot-to-dot shape but is nearby - like it might be at a distance watching the bear-shape. So that is how it got its name.

These days we don’t see bears in our gardens quite so often and street lights make the night stars a bit harder to see and so the dot-to-dot bear shape is harder to notice. I am sure you have seen another shape up in the sky that we would both recognise. To me it looks like a saucepan and handle. To others it looks like an old-fashioned plough; the type that used to be pulled by horses on farm fields. Have you seen that shape before? It is called The Plough or The Big Dipper and is actually part of the nose and back of the big bear. Don’t worry if you you can’t see the whole bear - I still can’t make out all of it either. The Plough shape is often found high in the Northern part of the sky. I made a picture of the shape so you can look at the night sky and find it yourself one night:

So if that is the nose of the bear then where is the bear-watcher? It is not so far away. If you draw an imaginary curved line using the curve of the saucepan’s handle to guide you then you will find a very bright star a little distance away. People who like watching stars remember this way of finding it by saying they arc to Arcturus. Look at the dotted line curve on the diagram and follow it to the bright star.

Arcturus is the fourth brightest star in the sky. Two of the even brighter stars can only be seen in places much further south than where I live in England and so, for me, Arcturus is the second brightest star in my sky. The best time to see it is in the Spring and Summer.

I really hope that you get a chance to see it for yourself in your sky because I want to talk more about it another time and I want you to know that it is a real thing. Not something that someone made up in a story. But I will understand if you don’t get a chance to see it by the time I next write. If fact, the difficulties of being able to see the stars when you are young is what I will talk about next time.

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