Earth rotates on its polar axis once every 23.9345 hrs. As an oblate sphere measuring a circumferential 360°, Earth rotates through almost 15 angular degrees per hour.

Local noon occurs when, on the hypothetical celestial sphere, the Sun is at the highest point during its daily skyward arch from east to west. When the Sun is at its zenith on the celestial meridian, this is termed local noon. In the extreme, every line of longitude, or fraction thereof, has a different local noon. In practice, however, because of Earth's angular rotation rate, it is more convenient to create a system of 24 time zones—each spanning 15 angular degrees. The central line of longitude in these zones establishes the local noon for individual time zones.

Earth's lines of longitude (meridians) are great circles that meet at the north and south polar axis. They are referenced by an east or west displacement...