Planet Earth has several concurrent motions, which determine the duration of the day and the seasons. The main motions of the Earth are represented by the:
- Rotation, or the movement of the Earth around its axis, e.g. one complete rotation of the Earth on its axis;
- Revolution, or the movement of Earth around the Sun, e.g. one complete orbit of the Earth around the Sun.
The image provides a graphical representation of Earth's axis describing the relations between axial tilt (or obliquity), rotation axis, plane of orbit, celestial equator and ecliptic. The Earth is shown as viewed from the Sun, the orbit direction is counter-clockwise (to the left). Earth's axial tilt is about 23.4°. It oscillates between 22.1° and 24.5° on a 41,000-year cycle and is currently decreasing (text and image source: Wikipedia, NASA/Dennis Nilsson via Wikimedia Commons).