This accessible problem will hopefully lead students into the whole area of solar and astronomical scales. The internet is full of sites offering information. Google anything and you'll start a trail of enquiry.

The methods often take some thinking about and nearly all of them require the imagination of different viewpoints. Grasping the methods and especially the required adjustment of perspective will not be immediate for most students and serves as a useful reminder that mathematical understanding isn't an "instant" or "not-at-all" experience.