The Universe is all of time and space and its contents. It includes planets, moons, minor planets, stars, galaxies, the contents of intergalactic space, and all matter and energy. The observable universe is about 91 billion light-years in diameter. The size of the entire Universe is unknown.
The word universe derives from the Old French word univers, which in turn derives from the Latin word universum.
What How Why
It takes the Earth 365 days and six hours to orbit around the Sun. The Six extra hours cannot be counted on the calendar. So, to keep an accurate count, an extra day is added at the end of February every four years.