You might like to know that we will be nearing the outermost limits of the solar system soon. Around a light years or four trillion miles from the sun are the first traces of the solar system, the Oort cloud.
"Are we really going to go through a cloud?"
Well, a sort of cloud, named after Professor Jan Oort.
"So why can't I see anything?"
No-one has ever seen the Oort cloud, but if it didn't exist someone would have had to invent it.
"So did Mr Oort invent it?"
Not exactly, he theoretically deduced its existence in 1950.
“So what is so special about this cloud?”
Well it's really just a collection of lumps of ice and rock, which never formed into a proper planet and drift around just about under the control of the sun's gravity.
“The gravity of the sun can be felt at this distance?”
Well, gravity is pretty weak out here but still strong enough to stop this space junk from drifting off into intergalactic space. What makes this cloud interesting is that every now and then a slight change in the balance of the sun's gravity and gravity from the rest of the galaxy gently nudges one lump onto a new path towards the sun. It picks up speed and heads off into the inner solar system.
“What happens then?”
When it gets nearer the sun the lump starts to evaporate and give off gases and dust that stream behind it. This is what comets are. This tail begins to glow and can reach millions of miles in length. Then it starts the slow journey back away from the sun and it starts to fade away again. Sometimes a comet is caught in an orbit so that it can go back again and again, like Halley's Comet which appears every 75 years or so. This was one of the important tests for Newton's theory of gravity. Edmund Halley, a friend of Isaac Newton, became famous for correctly predicting that a comet, which became known as Halley's Comet, would return in 1758.
“You said before that Newton almost never smiled, that must have pleased him.”
Sadly both he and Halley were dead by the time the comet came back, but at least Halley's name was remembered as the comet was named after him. His prediction showed that rather than being signs from God, comets were just another part of the solar system. But they are still very impressive.
“So what exactly is a comet made from?”
Well no-one really knew for certain until twenty years when the European Space Agency sent a probe called Giotto into space in 1986 that flew past and took photographs of Halley's Comet.
“What did it look like close up?”
Here's one of the pictures, there are a bit fuzzy but they showed that Halley's comet was a 10 mile long peanut shaped ball of ice and dust covered in soot.
“A great big dirty snowball?”
Basically yes, but as it heats up near the sun some of the contents get heated up and burst through the outer layer and that makes the tail of the comet as it escapes into space.
“Did I miss something, or did you forget to explain how Mr Oort worked out that his invisible cloud existed?”
Oh, sorry. Mr Oort deduced that this cloud had to exist otherwise there wouldn't be any comets left by now. Every time a comet comes by the some a lot of it melts. They lose so much of themselves on each pass by the sun that any comets that existed when the Earth and the rest of the planets were made, at least 4.5 billion years ago, would have long since evaporated into space. So there needs to be a place where comets can have stayed hidden away for a few billion years and that place is the Oort cloud.
“But no-one has ever been out this far?”
Not at all but there is one man made thing that is rushing out of the solar system, even though it has only gone 9 billion miles from the sun so far.
“Nine billion miles isn't bad.”
Not at all and it's now travelling at a million miles a day.
“Is this a space ship?”
More of a space probe than a space ship, Voyager 1, has been travelling through space for thirty years now powered by small nuclear power supplies and will head on out of the solar system eventually.
“When will it reach the nearest star?”
It might be 40 or 50 thousand years before it could reaches another star with planets. But if it ever does reach an alien civilisation they will certainly know a lot about us before they arrive.
“Just by examining Voyager?”
Well the space probe itself will hardly impress them. By the time it arrives the radioactive power sources will be all dead but it will be like a message in a bottle. They also included a 12 inch gold plated record with lots of information about earth.
“Like an LP record? NASA sent an LP into space?”
They certainly did, along with a needle to play it and instructions.
“They will think we are primitive cretins”
Well this was 1977, and nothing electronic would survive tens or hundreds of thousands of years like gold covered metal disc. The technology is primitive but the information if they play it will tell them a lot more. It is a bit odd that it uses a speed that no record player on earth uses, 16 and 2/3 revolutions per minute.
“What sorts of information was on this record?”
Well, a greeting in 55 languages.
“Will anyone one understand it?”
Well they are a few languages that no-one one Earth speaks like Akkadian which died out about 4000 BC. There are also the sounds of different animals, babies crying and a tractor. There are also 115 different pictures. Surprisingly detailed pictures of how humans reproduce. You can look at all these sounds and images at http://re-lab.net/welcome/images.html. Before you rush off to explore that here is the speech that US President Jimmy Carter recorded for the Voyager recordings.
“Of the 200 million stars in the Milky Way galaxy, some—perhaps many—may have inhabited planets and spacefaring civilizations. If one such civilization intercepts Voyager and can understand these recorded contents, here is our message: This is a present from a small, distant world, a token of our sounds, our science, our images, our music, our thoughts and our feelings. We are attempting to survive our time so we may live into yours. We hope someday, having solved the problems we face, to join a community of galactic civilizations. This record represents our hope and our determination and our goodwill in a vast and awesome universe."
Oh, and they also included a map to help any aliens find the sun and our planet in case they like the look and sound of us and decide to visit.
“Do you think aliens will ever find it and come to see us?”
If aliens do and find us first then that will mean they are a much more advanced species than we are, so I hope they will treat us lowly humans better than we have treated a lot of species that we consider simple. They might regard us as not much better or more interesting than pets if we are lucky.
“And if we are unlucky?”
If we are unlucky they will treat us in the same way that humans have treated of a lot of other species, they will either eat us or destroy us. That golden record contains anatomy pictures of what the insides of our bodies look like and even the structure of DNA, so they will certainly know if we look tasty.
[p.s. Voyager has featured in a lot of Sci-Fi films and most recently in the Futurama episode called Parasites Lost where Voyager ends up like a celestial space bug smashing into the Planet Express spaceship only to be cleaned off the windscreen by Leela.]
This is the story of a great journey that started with a great thought. One day in 1895 a boy looked into a mirror and wondered what the universe would look like if he could travel on a beam of light. That sixteen year old boy was Albert Einstein and that one thought started him on the road to discover his Theory of Relativity. The great man has been reinvented as Albert 2.0 to come back and blog about a journey through space on a beam of light and explain the science behind everything from atoms, blackholes to global warming. If you've just joined and want to start at the beginning use the index on the left. If you're bored try these links below just for fun.
UNSCRAMBLE EINSTEIN'S BRAIN
PRACTISE SAVING THE WORLD FROM ASTEROIDS
ALIEN CONTACT CALCULATOR
HEAR THE REAL EINSTEIN TALK ABOUT E=Mc2.
Saturday, July 21, 2007
Wednesday, July 18, 2007
“So can we see the earth from here?”
We're still too far away to see the earth, but we're heading toward that yellow star straight ahead. That's the sun.
"It doesn't look very special, just a normal looking star."
That's because it isn't really special, other than being home to us humans. It's just a nice, ordinary, stable star. Just the sort you’d want to live near. Not too big and not too small. Not a bad place to live around.
Not really, a typical quiet galactic suburb only thirty thousand light years from the centre of the galaxy.
“It's not as impressive as the star we came from.”
No, it's tiny compared to Deneb, but remember that big stars burn their nuclear fuel much faster. If the sun wasn't so average star we wouldn't be here talking about.
The sun's been burning for over four billion years and it took one and a half billion years for the earth to cool down and primitive life to start. Deneb will have blown up before life could possibly start. Even though the sun's not huge it's still brighter than most of the stars in this neighbourhood. Here is a map of this part of the galaxy from www.atlasoftheuniverse.com. We're just over 12 light years away now and this shows all the stars that are around the sun. If we humans ever get to travel into the galaxy these are the first stars they will reach.
“So which is the closest star?”
That little brown one over there, called Proxima Centauri. That's just over four light years from the sun but a rather dull little star. The one just near it called Alpha Centauri is almost a twin of the sun, it is exactly the same type of star.
“They still all just looks like dots of lights. When will the sun stop looking like star and start looking like the sun?"
Well, if you only had a pair of human eyes then you'd need to be within 5 billion miles.
"That's nothing. It’s...it’s...less than a thousandth of a light year."
Very good, just under 8 light hours. That's why from Earth all the other stars look like points of light, they are simply too far away. See those two stars up ahead.
“The two little dim ones, I see them.”
Those two stars are a binary system, so they are going around each other. A lot of stars form that way. That system is called Cygnus 61 as it was originally thought of as one star which is the 61st brightest star in our constellation Cygnus.
“How can they be in our constellation if we have been travelling through three thousand light years of space to get here?”
The constellations are not real groups of stars but just appear close when we look into space from earth. Because all stars look like dots of light, when we look at them we can't tell how far they really are away. So our constellation Cyngus is made up stars that are scatted all the way from here back to where we started.
“Is that the same for all constellations?”
Nearly all of them. One of the most recognisable constellations Orion, the hunter, is spread out over a huge distance too. This picture show what the constellation looks like from earth and how the stars are really spread out in space.
“If all the stars look the same no matter how far they are away, how can you measure their real distance?”
Scientists have a few tricks for that but one of the best is called parallax. Move your head from side to side. What happens?
Don't things close up seem to move?
“Yes but that's because I'm moving my head.”
I know, but things close up seem to move more than things far away don't they?
“Yes, I suppose they do.”
Well the same thing can work for stars but rather than move your head you have to look from two different places millions of miles apart.
“Oh, that sound's very simple.”
Of course it is. You just have to wait 6 months for the earth to go half way around the sun and you will be looking from a position that over 160 million miles different. The most distant stars, like things on the horizon when you shake your head, will appear to stay still, but nearer stars will seem to move position over six months. From measuring that movement, which is called parallax, scientists can measure the distance of nearer stars very accurately. It's not just scientists that use parallax to judge distance, pigeons do too. That's one of the reasons they nod their heads.
“Wow, Albert. That's a bit random even for you. Explain that one to me.”
Well a pigeon has an eye on each side of its head which makes judging depth difficult. So by bobbing their heads as they walk they can judge how far things are away from them with parallax.
“I suppose I did ask.”
The Praying Mantis, a large insect does the same thing.....but perhaps we should come back to that some other time.
“I think so Albert.”