- Moon (Wikipedia)
The Moon is Earth’s only natural satellite. It orbits around Earth at an average distance of 384399 km (238,854 mi; about 30 times Earth’s diameter). The Moon is tidally locked to Earth. This makes the Moon’s near side face Earth always the same way, and synchronizes its rotation period (lunar day) to its orbital period (lunar month) of 29.5 Earth days. Conversley, the Moon’s gravitation causes tidal forces on Earth, which are the main driver of Earth’s tides.
- Giant star (Wikipedia)
A giant star has a substantially larger radius and luminosity than a main-sequence (or dwarf) star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsprung–Russell diagram and correspond to luminosity classes II and III. The terms giant and dwarf were coined for stars of quite different luminosity despite similar temperature or spectral type (namely K and M) by Ejnar Hertzsprung in 1905 or 1906.