Although it has been known for about 50 years, I had never heard it until this was on APOD a few days ago (https://apod.nasa.gov/apod/ap200603.html).  Venus is a rocky planet, like Earth, but is covered by thick clouds that obscure all details of the planet’s surface.  But using radio telescopes, astronomers were able to “see” some details, which pretty soon led to an amazing discovery:  Venus always shows us the same side.  More specifically, Venus’ orbit and rotation are synchronized with Earth such that every time Venus is at “inferior conjunction” (when it is closest to us), the same side of […]