A Briefer History of Time

The need for time-keeping:

• Dates for celebration days (religion)
• Phases of the moon
• Seasons - for planting, harvesting, etc.
• Changes in plant life, water movement (the Nile)
• Constellation movement

September (derived from the Latin for seventh) is the ninth month of the year, because the Romans originally excluded winter from the calendar entirely, as it was a time of inactivity. Those two months were added at a later date.

When all of the other months were adjusted to thirty or thirty-one days, February remained at 28, because it was sacred to the deities of the underworld, and should not be changed.

The so-called Gregorian Calendar was not adopted in Protestant countries until much later. Its introduction into Britain in 1752 led to antipapal riots because people believed that the Pope had actually shortened their lives.

Clocks must have a regular, constant, or repetitive process or action to mark off equal increments of time:

• Candles marked in increments
• Hourglasses
• Knotted cords in stone mazes filled with incense
• Movement of the sun across the sky

• Position of clock hands

3500 BC - Obelisks (tall shadow-creators similar in shape to the Washington monument)
1500 BC - portable Egyptian shadow clocks (sun dials, essentially)
1500 BC-500 AD - Clepsydras (water clocks, "water stealers")
600 BC - Merkhets (astronomical tool for nighttime hours)
300 BC - Hemicycles (sun dials minus the useless half)
150 BC - Astrolabes (measuring time based on the altitude of the stars)
30 BC - 13 different types of sun dials in Greece, Asia Minor, and Italy, per Vitruvius.
900's AD - pocket sun dials (just over an inch in diameter, status symbols)
1300 AD - large verge-and-foliot mechanism mechanical clocks (weight driven)
1500 AD - Spring-powered clocks and watches (until main spring unwound, could be miniaturized, unlike weight-driven clocks)
1656 AD - pendulum clock (first clock accurate to within 1 minute/day, first time seconds were actually counted)
1675 AD - balance wheel and spring assembly (still used in some watches today)
1761 AD - marine chronometer (useable on a rolling ship, and at night)
1855 AD - Greenwich Mean Time (GMT) recognized
1920 AD - quartz clocks (regular vibration of quartz crystals, magnet turns a small pinion activating the mechanical parts)
1949 AD - first atomic clock (based on ammonia atoms)
1955 AD - atomic clock based on cesium, more reliable
1967 AD - redefinition of the second, no longer based on the motion of the earth
1972 AD- Coordinated Universal Time (UTC) replaced GMT (UTC runs at the rate of the atomic clocks, but when the difference between this atomic time and one based on the Earth approaches one second, a one second adjustment - a "leap second" - is made in UTC.)
2002 AD - atomic clock keeps time to within 30 billionths of a second per year

http://physics.nist.gov/GenInt/Time/time.html
http://www.britannica.com/clockworks/main2.html
http://www.time.gov/