Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the world or the Blue Planet.
It orbits the Sun every 365 and a quarter days. That extra quarter of the day is counted for every four years as a leap year. Without a leap year, eventually the seasons will no longer correspond with our calendar.