About

This interactive is used in Chapter 16. If Earth really orbited the Sun, early astronomers reasoned, we’d be able to observe stellar parallax, or the apparent motions of stars created by our changing vantage point, as Earth orbited the Sun. The flaw in that reasoning was that stars were so far away, that those motions were unobservable. Now, with today’s technology, astronomers do measure these motions, and you can observe it with this Interactive. Some simple trigonometry is the basis for stellar parallax. Try it out here, and see how different-sized Earth orbits, the distance to the star, and the quality of the telescope impact your observations.