The Royal Observatory in Greenwich—home of the International Prime Meridian—has an exhibit on right now called “Measuring the Universe,” celebrating the upcoming Transit of Venus, which will take place in June. (Venus will pass directly between the Earth and the Sun, “appearing as a tiny black dot against the bright solar disk,” and will not do so again for 105 years.)
If you’re not headed to London any time soon, you can at least watch the video below, which explains with wit and verve how scientists are able to measure the distances to things as far away as stars and other galaxies. (I particularly enjoyed the lightbulb that runs away from you on its little tiny legs—thus appearing to get dimmer, and revealing to those who have already calculated its luminosity just how far away it’s gone.)
The video makes an excellent companion to the great interactive educational tool created by the teenage brothers Michael and Cary Huang, “The Scale of the Universe.” If you haven’t checked that out yet, it, too, is highly recommended.