I wish to share with readers of The Catholic Astronomer a little video my wife and I made for use in my classes. It is called “Playground Parallax”, and I think you might find it interesting. A major scientific objection to the heliocentric theory of Copernicus and of Aristarchus of Samos—the theory that said that Earth orbits the sun annually—was that if Earth moves then we ought to see annual changes in the appearance of the stars. These changes are called annual parallax. The answer to that objection was that the stars are so far away that the size of Earth’s orbit is nothing compared to the distance to the stars. But, as you will see, there was a problem with that answer, a problem made worse with the discovery of double stars.
The video is amateurish, and maybe some day we can make a better version. But check it out, because I think it will help people understand one reason why many serious astronomers once thought the Copernican theory to be bogus. (The double star discussion in the video relates to my earlier post, “Strange Tales of Galileo and Proving: Telescopic Evidence for Earth’s Immobility through Double Stars”.)