The Babylonians used a base-60 number system, which is the origin of our way of dividing an hour into 60 minutes and a minute into 60 seconds. The division of a day into 24 hours comes from various ancient 12-based systems and the tradition of dividing both day and night into 12 parts.
Time describes the apparent motion of the Sun around the Earth. The Sun would appear to orbit the Earth in 24 hours. In reality, of course, the Earth rotates around its axis, and the Sun only appears to move around the Earth.
The division of a circle into 360 degrees also comes from the Babylonian base-60 system (360 = 6 × 60) and likely also from the fact that it roughly corresponds to the number of days in a year.
From this we can calculate that the Sun moves across the sky… No, do not think of it that way. It is better to think that the projection point of the Sun on the Earth's surface moves as the Earth rotates. The projection point of the Sun—and in fact all celestial bodies—moves westward by one degree in 4 minutes on the equatorial plane. (24 × 60 minutes) / 360 = 4 minutes. From this we obtain the relationship between degrees and time. Hour angle can also be expressed as a time difference between two locations. Expressed in time, the hour angle tells how many degrees the Sun’s projection point would move in a given time along the equatorial plane.
360° corresponds to 24 hours.
1° corresponds to 4 minutes or 240 seconds.
1’ corresponds to 4 seconds.
1 hour corresponds to 15°.
1 minute corresponds to 15’.
1 second corresponds to 0.25’.
For example, 16° 07’ corresponds to 1 hour, 4 minutes, and 28 seconds. In other words, the Sun’s projection point moves across a 16° 07’ angle on the equatorial plane in 1 hour, 4 minutes, and 28 seconds.
Hamburg VII 2026