Marking TIME - Happy New Year
1/1/2010 by: Darleen Hartley
Years, days, minutes, nanoseconds. A fraction of a second from a historical perspective doesn’t amount to much, but can be critical to the functioning of a computer program. Synchronization of file updates across several computers, sequencing distributed procedures, and coordinating flight patterns in the air traffic controller’s booth, depend on accurate timing. Such problems are avoided by the synchronization of clock times in networked computers with the Network Time Protocol [NTP]. Coordinated Universal Time [UTC] synchronizes computer clock times to less than a millisecond. David Mills at the University of Delaware developed this Internet standard which has been refined over the past twenty years.
Marking time permeates, and heavily affects the human condition. Remember the hullaballoo over the year Y2K? The changing of years is represented by Father Time, a mythological figure. The event is cause for reflection and resolutions. We earthlings have always been obsessed with Time. Our technology for tracking it has progressed from sun dials, water clocks, and mechanical timekeeping devices to quartz, and atomic clocks.
Humans have developed complex techniques to measure this elusive element, Time. We have divided our world into 24 standard and 16 nonstandard time zones. Travelers, on-line publishers, and separated families must coordinate meetings, publication, and phone calls cross numerous time zones. The challenge of knowing what-time-it-is-where has been met by several software developers. WorldTimeServer is one website that maintains its own place-related time database. There, you can view time differences, including Daylight Savings Time, in various parts of the world.
Prague's Astronomical Clock. Photo credit: Petr Kratochvil
Before computers, centuries ago, time was related to the cycles of the universe, agricultural planning, astrology, and superstition. Amazingly a clock made in 1410, the Prague Astronomical Clock, continues to function. Joseph Siry of Rollins College explains how it works "…there are three great co-axial wheels of the same diameter, driven by the same pinion, with 365, 366 and 379 cogs. The first of these gearing the zodiac and the indicator … rotates once a sidereal day. The second gears the indicator of the Sun and rotates once a mean solar day. The third gearing the Moon's pointer rotates accordingly with the mean apparent motion of the Moon."
Less complex, the ancients used a simple stick and its shadow to track the sun’s movement. The Egyptian obelisk, a fancy improvement, was a more stable measuring device. From this, smaller sun dials evolved with equi-distance markings. When, where, and who developed such instruments is debated, but the sequence of events [Egyptian Obelisk PDF Download from NIST] holds true.
The next technological advance, the water clock, came along before 2,000 BC in India and Mesopotamia. Sun dials were the basis for calibrating the water clocks. Water, dripping from an upper vessel into a bottom vessel which filled at a constant rate, reached markings that incrementally measured the passing of time.
Interestingly, clocks of this nature were used to limit visitation time in Greek brothels, around 350 BC according to Water-Clocks and Time Measurement in Classical Antiquity by John G. Landels in Endeavour a quarterly scientific magazine. Herophilos, a physician/anatomist, used the device to measure his patient’s pulse rate. Innovations in timekeeping waned for almost a thousand years. Looking around in the 14th century, you would find large mechanical clocks in city squares. Don Rathjen from the Exploratorium Teacher Institute describes the guts of a mechanical clock: "All mechanical clocks include some sort of escapement mechanism, whose function is to control the energy the clock receives, and portion it out into small regular bits of movement. The term escapement is associated with regulating the "escape" of energy from the weight or spring." An escapement [PDF download] includes a gear with teeth. An anchor which interacts with the teeth is attached to a pallet. As gears move, the mechanism marks the passage of time. Tick, tock.
The German Henlein replaced heavy drive weights by springs, spring-powered clock which made smaller, portable timepieces possible. Blaise Pascal, whose name graces a familiar computer language, supposedly was the first person to wear a wrist watch, tying his pocket watch with string to his wrist.
The pendulum clock designed by Dutch scientist Huygens, was a major improvement, however, friction was still a problem .This pendulum clock achieved a daily error of only 10 seconds. Scientists were developing quartz clocks in the 1920’s, the first step towards today’s atomic clock. Quartz clocks operate using the piezoelectric property of quartz crystals. The crystals when stimulated vibrate, generating an electric signal of comparatively regular frequency that operates the clock, without gears or escapements.
Size, shape, and temperature of the quartz determine frequency. An atom of hydrogen or caesium was considered to be more stable. The first atomic clock, in 1949, was based on ammonia. The National Physical Laboratory in England built the first practical cesium atomic frequency standard. Caesium standards replaced those of the original design. By 1960, they were incorporated into the official timekeeping system of the National Institute of Standards and Technology [NIST].
NIST is a non-regulatory federal agency within the US Department of Commerce which promotes innovation and industrial competitiveness by advancing measurement science, standards, and technology. The cesium atom’s natural frequency was formally recognized in 1967 as the new international unit of time, and the second was defined as exactly 9,192,631,770 oscillations or cycles of its resonant frequency, replacing the old second that was defined in terms of the Earth’s motion.
Time pieces started small, grew to gigantic proportions, and have again been minimized by technology. A prototype introduced in July 2008 was a translucent watch designed for the thumbnail, the TX54, which never made it to market apparently. However, atomic watches¸ even those that talk, are plentiful, if tracking time is a critical part of your life.
NIST, Huygens, Landels, Pascal, Joseph Siry, Prague Astronomical Clock, David Mills, Network Time Protocol, NTP, UTC, Y2K
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