Part 7/12:
For years, it was believed that Mercury was tidally locked to the Sun, meaning the same side always faced the star, similar to the Moon with Earth. However, radar observations in 1965 revealed that Mercury actually maintains a 3:2 spin-orbit resonance—rotating three times on its axis for every two revolutions around the Sun. As a result, Mercury experiences a solar day (sunrise to sunrise) lasting about 176 Earth days, much longer than its year.