Time

Time is a critical element for your computer and is one of the easiest things to set automatically. Here is information about time and how to keep your computer on time.

W32time is a time service you can use in Microsoft Windows 2000 to automatically set your computer's clock to the right time.

Windows XP has a time service built in, which is documented by Microsoft in the horribly technical page titled How to synchronise the time with the Windows Time service in Windows XP and again in the equally technical page titled How to configure an authoritative time server in Windows XP.

Windows 98, 95 and 3.1 can use free software from NIST Internet Time Service.

Linux and Unix let you set up both an NTP based service to set your clock and an NTP server to provide time to other computers. If you use Linux or Unix for a firewall then set up an NTP server at your firewall. Read more at Linux Time.

Apple's Mac had a time service added in version 8.5 of the Apple Mac operating system. Apple then threw out the Apple Mac operating system and switched to Unix, which has NTP already available. See the Linux Time page for Linux and Unix variants including OS X. NIST Internet Time Service has a page on the original Mac OS including versions prior to 8.5.

The best known long term time service is the Royal Observatory, Greenwich. America developed an equivalent to Greenwich with their U.S. Naval Observatory and their Time Service Department. The American civilian equivalent to their Navy time service is the Time & Frequency Division of NIST, the National Institute of Standards and Technology.

History of Time

13.7 Billion Years BC

Our measurement of time starts with the big bang that formed our current universe one sunny morning 13.7 billion years ago. Measurements before then are theoretical because the laws of physics are unknown beyond that point. The sunny morning was not sunny because stars did not form until hundreds of millions of years after the big bang and the morning was cold because the first infrared energy did not escape the big bang for thousands of years. Overall the neighbourhood around the big bang was pretty boring for many years, no broadband access and you could not find a decent espresso, then it became too hot and awash with unfriendly radiation.

3100 BC

Five thousand years ago the early farmers were tracking the days of the year to decide when to plant crops. The Egyptians used a lunar calendar with 29 days per month but that did not help them predict the most important event, the start of the annual flooding of their agricultural land by the Nile river. In 3100 BC the Egyptians realised that the star Sirius rose next to the sun at the start of the flood season. The Egyptians then adopted a calendar with 12 months of 30 days plus five extra days of religious celebrations. They did not use a leap year which made their new calendar go out of date by one day every four years.

Several middle eastern countries divided the day into 12 hours and the night into 12 hours, which produced a variable length hour as days expanded and contracted across the seasons.

30 BC

The Egyptians ended up with three calendars, the original lunar calendar that was still used for festivals and by the public, the rising of Sirius to start an agricultural year of three seasons, the flood, the crop growing season, and the harvest, plus there was a government calendar that lost track of time by one day every four years. The Egyptians corrected the mistake by adopting a leap year in 30 BC.

725

In 3500 BC the Egyptians built obelisks, pointy stone pillars, to form sundials. Other attempts to measure the time of the day include water clocks, sand clocks, and candles marked with units of time. Around 725 AD the Chinese invented the modern mechanical clock movement and used it in water powered clocks. At last we have a clock that goes tick tock.

1500

Peter Henlein of Nuremberg, in 1500 AD, invented a clock powered by a coiled spring which lead to the invention of the small, light, portable clock we call a watch. Rich people no longer had excuses for being late to parties.

1656

Christiaan Huygens invented the pendulum clock in 1656 which was accurate to one minute per day and he later refined it to 10 seconds per day.

1675

King Charles II of England decided to build a better observatory and founded the Royal Observatory at Greenwich. The longitude measurement line at Greenwich became the Prime Meridian line, the official start of the day and all measurements of longitude. Greenwich Mean Time is measured from the prime Meridian.

1761

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John Harrison developed new methods for reducing friction in clocks and in 1761 built a marine chronometer accurate to one fifth of a second per day, which is ten times more accurate than is needed to measure longitude for marine navigation. Read the fascinating story of John Harrison in [amazon 0140258795 title] by Dava Sobel. John's original chronographs are on display at the Royal Observatory, Greenwich.

1920s

The quartz crystal clock was invented in the 1920s. Piezoelectric electric quartz replaced the pendulum with a quartz crystal that vibrated thousands of times per second using a tiny amount of electricity and paved the way for quartz crystal watches that ran for years on one tiny battery with an accuracy of better than a second per month. The accuracy depended on tuning the crystal but the tuning could be performed automatically in the factory.

1955

The National Physical Laboratory of England built the first working caesium atomic frequency clock, which became the world standard, in 1955. NIST and other organisations joined in with a network of caesium clocks that cross check each other.

Atoms vibrate at fixed frequencies based on their energy level. Regular clocks vary in accuracy based on temperature as components expand and contract. Atoms jump up and down in energy in steps based on the number of electrons and their position. Because the energy changes levels in steps, you can keep an atom vibrating at exactly the same frequency across a range of temperatures easily achievable with regular air conditioning. Some atoms react to light by jumping up in energy when hit with light and then dropping down to emit a photon. You can easily keep light out of the atoms in an atomic clock. Cesium is stable and is easier to use than hydrogen, which is proposed as the ultimate standard for time.

1967

In 1967 the second was defined as 9,192,631,770 oscillations of a caesium atom. The current caesium clock at NIST is accurate to a thirty billionth of a second per year and is the source of time for the time server known as time-a.nst.gov. Geeks at NIST have no excuses for being more than 30 billionths of a second late to parties.

1986

In 1986 Timex released the Triathlon, the first really practical quartz watch for people who ran in the rain, sweated, and jumped in the ocean. My old Timex Triathlon watch started life in 1986 and survived marathons, mountain climbing, banging around in the bottom of suitcases full of computer hardware, plus scuba diving to well below the Triathlon's 50 metre limit, yet the watch kept on displaying the time within a second per month for 15 years using just three batteries. Poor wet marathon runners no longer had excuses for being late to parties.