Hour

Evolution of hour

Latitudes form a ring around the earth. At 0° latitude the ring is the largest and 90° latitude is small as a dot. It is a construction of multiple rings above and below the equator.

In primitive days seven rings above the equator were given names inspired by rings made by seven celestial bodies in the sky.

Saturn which makes the largest ring gives it’s name to the base ring on the ground forming the horizon. In the order of sizes,  above it jupiter, mars, sun, venus, mercury and moon are designated at equal intervals. The moon is at apex that is zenith.

This structure is used to describe the position and progress of celestial objects.  As it is not possible to locate the rings, the section following a ring is called by the same name. Any position is estimated from horizon or zenith using the names in the above order.

There are six sections between the seven rings and the seventh section falls beyond. But celestial objects progress beyond the apex down to horizon at opposite side. The progress is linear and the sections are equidistant. So the first section in the downward movement gets the name of seventh ring at the apex, in this case moon.

As the size of the ring is no more useful as the sequence of names has been ordered using the size of rings, the names in same order can be recycled.

Again starting with saturn from next section and continuing to complete the full circle with recycling, the first section in the next round will be sun section.

Thus a day consists of 24 sections and is known by the name of it’s first section. Succeeding days have the fourth name from that of previous day.

It all started like this and over a time the sections were numbered and seventh section was dropped for convenience and uniformity.

Days continue to have the fourth name from previous day.

An hour (symbol: h; also abbreviated hr) is a unit of time historically reckoned as 1⁄24 of a day and defined contemporarily as exactly 3,600 seconds (SI). There are 60 minutes in an hour, and 24 hours in a day.

The hour was initially established in the ancient Near East as a variable measure of 1⁄12 of the night or daytime. Such seasonal hours, also known as temporal hours or unequal hours, varied by season and latitude.

Equal hours or equinoctial hours were taken as 1⁄24 of the day as measured from noon to noon; the minor seasonal variations of this unit were eventually smoothed by making it 1⁄24 of the mean solar day. Since this unit was not constant due to long term variations in the Earth's rotation, the hour was finally separated from the Earth's rotation and defined in terms of the atomic or physical second.

In the modern metric system, hours are an accepted unit of time defined as 3,600 atomic seconds. However, on rare occasions an hour may incorporate a positive or negative leap second, effectively making it appear to last 3,599 or 3,601 seconds, in order to keep UTC within 0.9 seconds of UT1, the latter of which is based on measurements of the mean solar day.