Chris -  Well, if you think about what light is, light’s a wave.  It’s an electromagnetic wave which wiggles its way through the atmosphere, through space.  When it hits something transparent the wave hits that substance and it goes through it.  As it goes through it the wiggling of the wave makes the particles in that substance wiggle as well.  That includes the electrons. 

If the substance is transparent the wiggling of the electrons regenerates the wave of light goes through the substance, albeit with a time delay, which is why the light slows down a bit on its way through.  When it comes out the other side it’s recreated again with no loss of energy.  What about if the substance isn’t transparent, in other words, if it’s opaque?  Well, of course it reflects light and that’s gives it its colour.  If it reflects no light, it’s black.

We recently featured on this show the darkest substance in the Guinness Book of Records ever.  Pulickel Ajayan produced this substance.  He’s at Rensselaer Polytechnic.  The way he did that was by producing these nano-tubes: a forest of bamboo-shaped nano-tubes.  These are tiny skeleton tubes like straws of carbon.  They’re literally thousands of times thinner than a human hair.  By making a sea of these things, when light goes down into this, ricochets off a nano-tube and bounces into another one it just gets lost.  It gets trapped inside so nothing gets reflected.  That makes the substance very, very dark.  When light gets soaked up by a substance, basically what it’s doing is all the energy (the vibration of the light) is making the atoms in that substance vibrate.  It’s making heat.  That’s why solar cells that are made of black stuff get warm, because they’re soaking up the light energy and radiating very little out.

When a substance is radiating other colours what’s happening is that some wavelengths of light, some wiggles are absorbed and they turn into heat in that substance whilst others are reflected.  When they’re reflected, basically the wiggle the wavelength imparts to the material creates another light wave of the wavelength of the colour that you see.  That’s why it reflects light of that particular colour.  With white the substance is very good at reflecting all wavelengths of light which is why if you add all the wavelengths of light together you see white.  That’s why it looks white.  That’s why water is clear when you shine light into it but snow crystals are white because with water light can pass straight through.  With snow crystals light bounces around all over the place so all the light gets returned to you so it looks white. Helen -  So it’s all about what different substances are made of and how they vibrate?Chris -  Yes, the different substances will soak up different light of different wavelengths, different frequencies but not others.  Different colour lights have different frequencies to each other and some will be soaked up by the surface and others won’t.

We put this question to Chris Davis:

The reason is that when you have these magnetic fields releasing it releases an intense storm of particles. It’s called a coronal mass ejection to scientists which is a very dull name for anything. Actually it’s a billion tonnes of material travelling at a million miles an hour. It contains about 100 times the energy of the world’s entire nuclear arsenal. Although it’s spread out over an extremely wide region in space if that magnetic field is in the opposite sense than the magnetic field on Earth then we all know from school that magnets of opposite polarities attract. Magnets of similar polarities repel. If they’re opposing polarity the two magnetic field can interact and that allows all this hot material to interact with the Earth’s atmosphere .

We put this question to Chris Davis:

It certainly happens if you burn hydrogen to form helium the star is the consequence of an equilibrium of forces. You’ve got the gravitational collapse of that body of gas, pulling inwards on it and heat generated by the nuclear reaction in it pulling the star out. You’ve got to have an intense amount of pressure in the middle to force hydrogen nuclei close enough together to form helium. There are various other burning cycles. You can burn helium to produce carbon but eventually when all the fuel is used up in the core there is no forcing out of the star. Gravity wins out and it collapses the star in on itself. When this happens, very briefly you get a large increase in density in the star’s core. That can generate these much heavier elements and then the star will explode.

Chris -  So you can look at it as the stars are the uteruses of the universe, they give us everything that we’re made of?Chris D -  That’s true. The star isn’t going to be completely burned to the other element. There is going to be a large amount of hydrogen. Also, the universe is still very much dominated by hydrogen gas which is the primal fuel for stars. That dust, that matter, the heavier elements will be spread out into space. Some of it will contaminate the next generation of stars.  As another cloud starts to collapse together under its own [gravity] you’ll get some of that heavier element polluting, if you like, the new star that’s formed. It won’t be pure hydrogen to start with and you’ll still have the majority of the gas will be hydrogen but with the heavier elements surviving.

We put this question to Chris Davis, from the Rutherford Appleton Laboratory:

That’s very interesting. It all depends at what frequency their equipment’s working at but the radio station’s reflected off the Earth’s ionosphere which is an electrified layer on the edge of space which is where the aurora interferes with. The ionosphere by night can reflect radio stations over large distances and during the day they’re much more absorbed in the lower atmospheres. It sounds like, if they’re going out around dawn it might just be around the time these radio stations are changing and they’re picking up signals from a distance when they wouldn’t normally expect to.

We put this question to Stuart Clarke, author of 'The Sun Kings":

Stuart - It’s certainly possible if you’re looking for planets in the whole galaxy you’ve got about 100,000 light years to imagine the size of telescope you’d have to build to actually see a planet 100,000 light years away is just so large. All the ones we’ll look at will be only a few tens of light years away.

Chris -  There is theoretically the possibility that we should pick up a star that turns out it should have some habitable planet around it but by the time we get to when we can see anything useful that star could have blown itself up.Stuart -  yes, the upside is that allows us to do cosmology because the farther we look into space the older the objects get we can do the archaeology of the heavens. Chris -  Are people looking at that?Stuart -  Exactly, that’s how you do galaxy evolution. You just look for galaxies farther and farther away and know that’s how they looked billions and billions of years ago.