3  Putting the ingredients together

You’ve seen that the cross-section of a sphere is a circle, and you’ve seen how to work out the area of a circle. You’ve seen that a transit allows us to work out the relative sizes of a star and an orbiting planet, based on the fraction of the star’s light that is blocked by the planet’s silhouette. Finally, you’ve learned that the size of a star can be gauged using spectroscopy, i.e. studying the finely spread rainbow of light from the star. This last point is something that can’t really be proven here, but if you study more astronomy you will learn how it’s done.

In the remainder of this week’s work you will be putting these ingredients together to develop a recipe that allows direct measurement of the size of some exoplanets, even though the planets themselves can’t be seen.

Next you will see how astronomers detect and interpret transits. You will begin by considering some of the practical aspects, and then you will look at the underlying maths.