This week's programme is all about meteorites and asteroids. Not too far from the Rough Science base on the edge of Death Valley is Meteor Crater. Iain, Kathy and Mike have to work out how big the meteor that caused this huge crater must have been. But it's not just the Earth that gets hit by objects from outer space - the moon is also a target, as evidenced by its heavily cratered surface. So Jonathan and Ellen have to pick a crater on the moon - any crater will do - and measure how big it is. And because they'll be doing their measurements at night, Ellen has to come up with some lights. The Meteor Crater team decide they have to split their work. Kathy and Iain head off to the crater itself to try and measure its diameter. This is the first essential step if they are to work out how big the meteor was that caused the crater. At the same time, they are hoping to find out more about the meteor in the hope this will give them clues about its size. Meanwhile Mike stays behind to try and make his own crater. He performs a series of impact experiments, dropping heavy objects into sand in an effort to work out the relationship between the size of an object and the size of crater it forms. Jonathan and Ellen have been given a high quality optical mirror, and so to find and measure a crater on the moon, they build a reflecting telescope. Their plan is to time how long it takes the whole moon to travel across a fixed point in their eyepiece, and then time how long it takes their chosen crater to travel across that same fixed point. Because they know that the moon is 3500 kilometres across, they can use this as a starting point to calculate the diameter of the crater. For her lights Ellen heads to the hills and collects pine sap. She melts it to remove some of the most volatile compounds, and then uses bark fibres as wicks, to make highly effective Rough Science candles.