Yes, basically.  The Big Bang produced hydrogen, helium, and as we mentioned earlier, a little bit of lithium.  But most of the other elements, in fact all the other elements, had to be made somewhere, and the answer is they were all made in stars.  And stars used fusion to combine a nuclear synthesis and supernova explosions to combine small elements to make bigger and bigger elements.  And so, all of the elements that make your body today were made in the birth, growth, and death of stars that lived billions of years before you did.  Isn’t that amazing? 

Well, by dust, we’re talking about small particles, because remember that when things form to start with, they don’t necessarily have to form big things and then be ground down into little things.  Small things will attract other small things because they’ll stick together, one way or another.  So when we’re talking about dust, we’re talking about amorphous materials that can include big bits, small bits, and bits of gas.  So it’s a way of not having to define exactly what that entity is, but saying it’s a mixture of chemical entities which have all of the necessary pre-requisite ingredients to actually form planets and stars.

The moon is orbiting the earth and rotating exactly once per orbit, this means that one face is always facing the earth. A similar example is if you get a friend to walk in a circle while always facing the centre, they are rotating once every orbit.

The obvious question is why did this come about, is it just fluke? 

It is all because of tides, the gravity from the moon distorts the sea (and to a lesser extent the earth itself) into an ellipsoid. As the earth rotates this distortion moves around the earth froming the tides. The energy to drive the tides comes from the earth's rotation and the earth is slowing down its rotation. We know that there were 400 days in a year 250 million years ago by studying corals.

The earth also creates tides on the moon, but because the earth is about 80 times heavier than the moon they are far stronger. Originally the moon was spinning, but these immensely strong tides required so much energy that the moons rotation slowed down so much it is now always facing the earth. Essentially there are still tides - the moon is distorted, but they are locked in one place - it is said to be tidally locked.

We posed this question to Dr Mark McCaughrean...

Yes, I think one of the things you have realize is that when the solar system was very young, it was very much hotter.  And so, you had a lot of water in the solar system, but out at about Jupiter was pretty much evaporated off or incorporated into places like the Earth.  But the comets are very big lumps of icy dust and muck still leftover from the early part of the formation of the solar system.  It’s just leftover stuff.

We posed this question to Dr Matt Balme...

Well, it’s a fairly simple piece of physics.  One of the things that keep on moving their orbit, there’s nothing to stop them.  I mean, they’re not hitting anything, so to speak.  So they’re not losing any energy, and they’re not losing, more importantly, angular momentum.  So angular momentum is a conserved thing.  It can’t just be taken away by, just by wishing it away.  It has to be taken away by things, and the Earth is just sitting there, rotating.  Nothing’s taking its angular momentum away except the Moon.  The Moon is actually going to steal some of the Earth’s angular momentum, slow it down, and at some point in the future, the Earth and the Moon will be locked together they would both have lost angular momentum.  At the moment, we only see one face of the Moon.  In the future, only one face of the Earth will be facing the Moon.  So we’ll only be able to see the Moon from one side of the Earth, and vice versa.

The main reason that stars look spiky is that the optical instrument you are looking at them with is not perfect. Because light is a wave, if you shine it through a small hole you get a pattern known as an interference pattern, this is because different light waves interfere with each other, making patterns of light and dark.

If the hole was circular you would get a relatively clean picture, but if it isn't then you will get various visual artifacts. These are much dimmer than the object itself so during the day you can't see them, but if a bright object is surrounded by darkness they are very obvious.

So if you look at a streetlight you often see streaks coming off it. If you squint, you make your pupil even less circular so the streaks get much stronger. The interference pattern will have a similar symmetry to the hole, so if you squint your eyes into a slit you get 2 strong streaks. Your camera doesn't have a perfectly circular aperture so you get streaks, the number will depend on the shape of the aperture.

Large telescopes need structures to hold their secondary mirrors, and it is the diffraction from these that you see in pictures from the Hubble Space Telescope etc.

Chris -  But the reason they’re actually twinkly when we look at them is nothing to do with that.  They’re twinkly when we see them through the Earth’s atmosphere because the Earth’s atmosphere is not uniform.  There’s air which is at hotter temperatures, and therefore, less dense, and there’s air which is at colder temperatures, and therefore, more dense.  And when light goes from a medium, which is more dense, into a medium which is less dense, it changes speed.  In fact, it speeds up a bit.  And it’s that change in speed that causes the light to bend a little bit.  And that means that when you see rays of light coming from a long way away, they appear to be coming from one place, and then another place, and another place, and then another because the light rays are being bent alternately as it goes in and out of warm and cold patches of the Earth’s atmosphere.  And that’s what makes the star twinkle.  And you see the same thing happening if you look at the lights from a harbour across a sea harbour or a port, for example.

Diana -   And you can also get polarised filters to put on your camera.  They will make the stars appear to point in numerous different directions, as well.

The answer is because the element puts so much energy into the water.  The water expands around the element to a point where it wants to boil.  It forms a bubble of water gas, steam.  And that bubble, as it rises through the water, then it gets cool, it collapses in on itself and does what's called cavitating.  It goes “bang”, or “pop” it’s a sort of reverse pop, and that’s the noise you can hear.

We put this to Dr Matt Balme,

Possibly, I think it's probably not the right reason though.  I think the reason sands on Mars are red is really just due to a magnetite composition or ferrous iron mineral composition.  You know, Mars may or may not have had an ocean.  If it did have an ocean, it probably didn’t exist for a very long period of time, relatively speaking, not like the Earth, which has been around for billions of years.  So you know, we’re loathe to rule anything out until we actually go there.  I mean, that’s one of the wonders of planetary science.  There’s an alternative answer to almost everything.