Earth Rotation Essays - Celestial Coordinate System, Precession

Earth Rotation The Earth is rotating around an axis (called its rotational axis). Some objects rotate about a horizontal axis, like a rolling log. Some objects, such as a skater, rotate about a vertical axis. The Earth's axis is tipped over about 23.5? from vertical. How do we define up and down in space? What would "vertical" mean? For the Earth, we can think of vertical as straight up and down with respect to the plane in which the Earth orbits the Sun (called the ecliptic). Earth's rotational axis always points in the same direction, so that the North Pole points towards the star Polaris. Think of the Earth as a spinning top, tipped over to one side. The Earth rotates around once in 24 hours - that's a rate of 1000 miles per hour!. The time it takes for the Earth to rotate completely around once is what we call a day. It's Earth's rotation that gives us night and day. The combined effect of the Earth's tilt and its orbital motion result in the seasons.