Chris - The answer is that heat arrives in the form of light because it’s in the form of infra-red radiation, largely, that’s reaching us from the sun.  It’s reaching us in the form of radiation so that too takes 8 minutes to get here.

We put this to Ed Tanner, Senior Lecturer in Plant Sciences at Cambridge University

I think the answer to the question about why closely related trees growing in exactly the same ground and the same climate have different-shaped leaves is actually that they don’t.  Because they’re closely related they are very similar.  For example, all oaks have broadly similar-shaped leaves because they share most of their genetic information.  Perhaps a more interesting question is why distantly related trees growing in the same ground and in the same climate have different shaped leaves.  The answer is it doesn’t matter very much.  As long as leaves are reasonably good at doing their job, which is fixing carbon dioxide in the atmosphere it doesn’t matter whether they are wavy at the edges or not wavy at the edges.  They have to absorb the light and once they’ve absorbed the light they would fix CO₂.  As long as they put their competitors in the shade any reasonably functioning leaf will do the job.  It matters where your leaves are in relation to other trees.  If you’re an ash tree you’ve got to be above an ash tree or if you’re a beech tree you’ve got to be above an ash tree.  It  doesn’t much matter what your leaves are like.

Chris - Well, we have to go by what the models are telling us and what samples we’ve got.  We’ve got a very large moon around the earth.  In fact, it’s unfeasibly large for a planet of our size.  Why have we got such a big moon where it is?  What the prediction is, and based on what we know about the composition of the moon from samples that the Apollo astronauts have brought back is that the moon is made of exactly the same stuff, give or take, as the surface of the Earth – the Earth’s crust.

The big question is how did something made pretty much of the same material as the Earth end up orbiting the Earth unless something bashed it an put it up there?  The best suggestion that scientists can come up with, based  on all the evidence we have, is that during the early phases of the formation of  the solar system (something like 4.5 billion years ago) there were two planets.  One a future Earth, one another planet which they’ve notionally called Thea.  These were very similar in terms of their orbital pattern.  One ran into another – it was like cosmic billiards that went on.  As a consequence of their massive great collision the cores of both planets effectively fused.   In the course of this collision a lot of the surface material from the  Earth got ejected into space and it formed a sort of shroud around the Earth which slowly coalesced in the same way that rings around Saturn have coalesced to what would have originally been an envelope.  They then coalesced and aggregated to form the moon.

It’s on the basis of there’s no other better explanation than that one to explain why we have this phenomenon of this big moon and what the moon’s made of.

Chris - This is a very difficult question o answer, or at least it was.  The problem is that if you’re  looking at stars in the night sky; if a star is at a certain distance from you its brightness can’t really be used as a measure of how far away it  is because a bigger star will be brighter and because light  gets dimmer the farther it is from you a big star can be a lot  farther away than a small star and yet they’ll both  appear exactly the same brightness.

How do you solve that one?

This kept astronomers guessing for a very long time until about the turn of last century.  A woman in contact with Hubble, after whom the Hubble Space Telescope is named, solved the problem.  Her name was Henrietta Levitt and she was looking at star charts.  She noticed that some star appeared to get bigger and brighter and then dimmer and weaker.  They did it with a regular period.  These have now become known as the stellar yardsticks.  They’re called Cepheid variables.  They’re stars that swell up and shrink down.  Because the period at which they do that varies with the size of the star you therefore know, if you look at how often a star like that is blinking on and off, you know how big it is.  Therefore you know how bright it is.  Because light follows an inverse square law you can work backwards to work out how bright that star must be and therefore how far away it is.

Scientists now use these Cepheid variables when they look at a distant star structure they can use the period of any Cepheid variables that are there to work out how far away those particular entities are.  That’s a stellar yardstick and it was solved by a lady at Harvard a hundred years ago.

Chris - The forum has come to our rescue to answer this one:  www.thenakedscientists.com/forum. There’s a terrific answer. RD points out that anything leaving the Earth into space needs to be travelling at escape velocity. That means 11.2km/s. To put that into perspective even a high-powered assault rifle probably fires things at 1km/s. It’s running significantly too slow in order to achieve escape velocity. It also doesn’t take into account air resistance. There’s a very good answer from BoredChemist. One thing to consider here is what about if we just build a powerful rocket and fire something from Earth? He says there’s a limit to how far you can get something to go and how fast you can get it to go using a gun.  The projectile is driven by hot gases producing the explosion but the gas is made of molecules and they have a range of velocities. The hotter the gas, the higher the average velocity. To a fair approximation, the average speed of the molecules is the speed of sound in that gas. A projectile is moving faster than that the gas molecules will get left behind so they can no longer push on the projectile to make it go faster. By fudging the issue and using hot light gases like helium you could make it go a bit faster. There’s no way that’s you’ll get to escape velocity. Sorry about that!