Mercury can be seen with the naked eye only at about this time. An occultation of a planet or star is an eclipse of it by some other body, usually the Moon. Stars are the basic units of population in the universe. Our Sun is the nearest star. Stars are composed of intensely hot gasses, deriving their energy from nuclear reactions going on in their interiors.
Galaxies are immense systems containing billions of stars.
The few exceptions are other galaxies. The spiral galaxy nearest to ours is in the constellation Andromeda. It is somewhat larger than our own galaxy and is visible to the naked eye. Astronomers have estimated that the universe could contain 40 to 50 billion galaxies. A black hole is the theoretical end-product of the total gravitational collapse of a massive star or group of stars.