Do you put on a watch? Think about a world with out it.
Beginning with nothing however the solar, moon, and stars, people have been getting a deal with on time for hundreds of years (together with after they invented the idea of a century). In the present day we’re going to try our species’ journey from sundial to the timing expertise present in our latest PNT product, the GNSS Disciplined Oscillator, which might measure time with sub-nanosecond accuracy.
Early Human Engagement with Time
The earliest strategies of measuring time had been carefully tied to pure patterns folks may observe occurring round them. The change from night time to day, the change from summer time to winter after which again once more; these cycles had been the primary strategies early people used to maintain time. Seasonal modifications had been vital for survival, influencing when to plant crops, hunt animals, or put together for harsh climate. These modifications had been typically marked by constant and observable environmental shifts — such because the migration patterns of birds, the flowering of crops, or the primary frosts. Individuals who lived close to water lived in sync with the rising and falling tides; an everyday every day cycle that varies throughout the month relying on the place of the moon.
Historic people additionally seen the patterns made by celestial our bodies: the phases of the moon, the positions of stars and planets all year long, and the patterns of eclipses and solstices. It is easy for us to say that the construction of the photo voltaic system or the connection between the Earth and Moon is frequent sense, however early people had been figuring all these items out from scratch. Think about seeing a complete eclipse with out realizing the moon’s relative place is what’s blocking out the solar – you’d suppose the world was ending too!
Time was additionally a social assemble, heavy with religious significance. Many prehistoric communities marked time not by minutes or hours, however by pure occasions and communal actions. Rituals, storytelling, and gatherings had been typically timed to line up with vital pure occasions, resembling full moons, solstices or eclipses.
The dearth of mechanical timekeeping throughout this period meant that folks lived lives that had been much less segmented and scheduled than in fashionable occasions. Work, social exercise, and relaxation had been fluidly built-in with the calls for of the setting and the group. This life-style fostered a special sense of time, one which was much less about counting hours and extra about dwelling in concord with the pure world.
The Invention of Timekeeping Units
Steady Timekeeping Units
Sundials
Sundials, which date again to historic Egyptian and Babylonian civilizations round 1500 BCE, offered a approach to measure time based mostly on the shadow forged by the solar. These gadgets divided the day into items, however depended completely on the presence of daylight, limiting their usefulness to sunlight hours and clear climate circumstances. They had been made by attaching a triangular piece that pointed to the North Star to a round base that had the hours marked on it. They had been created in various sizes, however the size of the shadow simply depends upon your latitude, and the angle of the shadow exhibits your time.
Enjoyable reality: the idea of the solar casting a special size shadow at totally different latitudes was utilized by Greek mathematician Eratosthenes to estimate the curvature of the Earth inside 2% of the at present accepted worth. Over 2000 years in the past. So uhhhh, any flat-earthers on the market seeking to “do your personal analysis,” go outdoors with a stick and a tape measure.
Water Clocks
To beat the restrictions of sundials, just a few cultures developed water clocks, or clepsydras, which allowed for time measurement no matter pure mild. They measured time by an everyday movement of liquid into or out of a vessel. Water clocks appeared in varied varieties throughout historic civilizations, together with Egypt, India, China, and Greece, every including nuances and enhancements. For instance, within the third century BCE, the Greek engineer Ctesibius of Alexandria included gear-wheels and a dial indicator to indicate time extra precisely in his water clocks, introducing a type of mechanization in time measurement.
Incense Clocks
Originating in historic China, incense clocks had been a way of timekeeping that relied on the gradual and constant burning of specifically designed incense sticks or powders. These clocks had been typically crafted with totally different scents that might launch fragrances or set off small bells at set intervals. They had been generally utilized in non secular ceremonies, houses, and imperial courts, as they offered a silent and pleasant approach to measure time. Their use was particularly priceless in Buddhist and Taoist temples, the place monks relied on them for meditation and prayer periods.
Astrolabes
First developed by Greek astronomers and later refined by Islamic students, the astrolabe was a complicated instrument used for figuring out time and celestial positioning. By aligning its rotating parts with the positions of stars or the Solar, customers may calculate native time, latitude, and even observe stars or predict astronomical occasions.
Astrolabes performed an important function in navigation, significantly for sailors throughout the Age of Exploration, as they allowed for correct sea journey earlier than the event of extra superior timepieces. They had been additionally utilized by students and scientists for astronomical observations, making them probably the most essential scientific instruments of the medieval world.
Candle Clocks and the First Alarms
Candle clocks had been an early and sensible approach to measure time earlier than mechanical clocks turned widespread. They labored by marking candles at particular intervals and utilizing the gradual, constant burning of wax to point the passage of time. Some variations included small steel pegs or nails inserted at set factors within the candle, which might fall onto a steel plate when the wax melted to make a sound that acted as an alarm or reminder.
These clocks had been particularly helpful in houses and monasteries, the place monks used them for preserving observe of prayer occasions at night time. Their simplicity and reliability made them an efficient timekeeping resolution in areas the place water clocks or mechanical gadgets had been impractical.
Hourglasses
The hourglass, first documented within the 14th century, was a exact and reusable system consisting of two glass bulbs linked by a slender passage. Effective sand contained in the glass would movement from the highest chamber to the underside at a constant fee, permitting customers to measure brief intervals of time precisely. Hourglasses had been extensively used aboard ships for navigation and timing ship duties, as they had been unaffected by the motion of the ocean.
In addition they performed a job in church buildings, the place they helped regulate sermons, and in scientific experiments requiring exact measurements of brief durations. Their sturdiness and ease of use made them a priceless instrument in an period earlier than mechanical clocks turned frequent.
Early Oscillating Clocks
Escapements
An escapement is a mechanism in mechanical clocks that regulates the discharge of power to make sure correct timekeeping. It controls the switch of power from an influence supply to the clock’s timekeeping aspect, permitting the gears to advance in a managed and periodic method. Basically, the escapement ensures that the motion of the clock is regular and doesn’t merely unwind abruptly.
The earliest recognized escapement mechanism was the verge escapement, which appeared in medieval Europe across the late thirteenth century. This technique consisted of a crown-shaped gear and a pair of pallets that oscillated backwards and forwards, regulating the motion of the gear tooth. The verge escapement allowed for the creation of the primary mechanical clocks, which had been principally present in church towers.
Later enhancements led to the anchor escapement, developed within the seventeenth century, which considerably elevated accuracy by lowering friction and enabling using the pendulum for timekeeping. This innovation, attributed to both Robert Hooke or William Clement, allowed clocks to attain a lot larger precision, resulting in the event of longcase (grandfather) clocks.
The escapement mechanism continued to evolve, with later developments such because the detent escapement (utilized in marine chronometers) and the lever escapement (utilized in fashionable wristwatches), every enhancing accuracy and effectivity. The invention of the escapement was a basic breakthrough in horology, reworking timekeeping from rudimentary gadgets into exact, mechanical devices.
Pendulum Clocks
A pendulum clock is a sort of clock that makes use of a swinging pendulum as its timekeeping aspect. The common, rhythmic movement of the pendulum regulates the motion of the clock’s gears, making it considerably extra correct than earlier mechanical timepieces. Pendulum clocks remained essentially the most exact timekeeping gadgets from their invention within the seventeenth century till the event of quartz and atomic clocks within the twentieth century.
The invention of the pendulum clock is credited to the Dutch scientist Christiaan Huygens, who designed the primary working mannequin in 1656. Huygens was impressed by Galileo Galilei, who had noticed the common movement of pendulums within the early 1600s and theorized their potential use for timekeeping. Nonetheless, Galileo didn’t full a working pendulum clock earlier than his loss of life.
Huygens’ design featured an anchor escapement, which allowed the pendulum to drive the motion of the clock’s gears with excessive precision. His pendulum clock drastically improved timekeeping accuracy, lowering errors to inside just a few seconds per day — far superior to earlier verge escapement clocks, which might be off by a number of minutes per day.
Pendulum clocks turned widespread in houses, church buildings, and observatories, resulting in additional refinements resembling grandfather clocks and precision regulator clocks, which had been used for astronomical observations. Though ultimately changed by extra superior applied sciences, the pendulum clock revolutionized timekeeping and laid the inspiration for contemporary precision clocks.
Precision Timekeeping
Marine Chronometer
The event of the marine chronometer was pushed by the longitude downside, a serious navigational problem ships confronted within the seventeenth and 18th centuries. Whereas latitude can simply be decided utilizing celestial navigation, sailors had no exact technique for measuring longitude, which required an correct time reference.
In 1714, the British authorities established the Longitude Act, providing a reward of as much as £20,000 to anybody who may devise a dependable technique for figuring out longitude at sea. Tobias Mayer, a German astronomer, devised a sequence of calculations that used the moon as a reference and had been capable of precisely devise longitude. The board claimed the calculations took too lengthy in order that they did not give him the award, though his widow ultimately received it after an extended battle for recognition after his loss of life.
A breakthrough within the type of a mechanical system got here from John Harrison, an English clockmaker who spent over three a long time designing an answer: the marine chronometer. Harrison developed a sequence of timepieces together with his last mannequin, H5 (1770), proving correct even beneath the tough circumstances of sea journey.
His improvements included:
- Temperature-compensated steadiness wheels to stop growth or contraction from affecting accuracy.
- Friction-reducing supplies to take care of precision over lengthy intervals.
- A high-frequency oscillating steadiness wheel, changing the pendulum (which was impractical on a rocking ship).
Harrison’s marine chronometers enabled sailors to find out their longitude by evaluating the native photo voltaic time to the reference time on the chronometer. This invention improved navigation, lowering shipwrecks and boosting international commerce and exploration. By the early nineteenth century, the marine chronometer turned a vital instrument on all main naval and service provider ships, laying the inspiration for contemporary GPS-based navigation.
Electrical Clocks
Electrical clocks, which used electrical energy to energy the clock mechanism, supplied larger accuracy and wanted much less upkeep than mechanical clocks, and marked an enormous leap ahead in timing expertise.
The primary main breakthrough got here in 1841, when Scottish inventor Alexander Bain developed a clock that used electrical energy to drive its pendulum and equipment practice. Not like mechanical clocks, which required frequent winding, Bain’s design used an electrical impulse to maintain the pendulum swinging, making it extra environment friendly and lowering timekeeping errors attributable to mechanical friction.
Over the following few a long time, electrical clocks turned extra refined, resulting in synchronization programs that allowed a number of clocks in numerous places to remain completely in sync. By the early twentieth century, these synchronized electrical clocks had been extensively adopted in railway networks, factories, and broadcasting stations, the place exact timing was important.
Quartz Clocks
Essentially the most revolutionary development in electrical timekeeping got here in 1927, when Warren Marrison, a Canadian engineer, invented the quartz clock. As an alternative of utilizing a pendulum, the quartz clock relied on the vibrations of a quartz crystal when subjected to {an electrical} cost.
Quartz was a fantastic materials to make use of for timekeeping for just a few causes: its measurement doesn’t change a lot beneath temperature fluctuations, and it has pizoelectric properties, which suggests it will possibly oscillate when affected by an electrical present. In practically all quartz clocks and watches, this frequency is 32768 Hz.
Whenever you hear “crystal” you may suppose your watch has a tiny model of these crystals you see folks carrying (and leaving out to cost beneath the complete moon), however that is not completely the case. “Crystal” refers back to the molecular construction of the quartz, but it surely’s reduce right into a tuning fork form at a really small scale.
These vibrations had been discovered to be extremely secure and allowed for a degree of precision that far exceeded mechanical clocks. Quartz expertise paved the best way for contemporary digital clocks, atomic clocks, and are current in most wristwatches these days.
Atomic Clocks
Quartz clocks had been fairly correct, however nonetheless misplaced just a few seconds each month, which provides up over time. One thing extra correct was wanted as science and expertise superior, and the atomic clock was born.
Atomic clocks got here into being because of developments in quantum mechanics, which allowed physicists to grasp and manipulate the properties of atoms at totally different power ranges. They are often so correct {that a} clock will lose lower than a second over tens of millions of years. The primary atomic clock was developed in 1949 by Dr. Harold Lyons, a physicist. This clock used an ammonia absorption cell to drive the frequency of a quartz oscillator.
Atomic clocks perform by measuring the exact frequency of microwaves wanted to induce a specific power state transition in atoms. The commonest kind of atomic clock immediately makes use of cesium atoms, particularly the transition between two power states within the cesium-133 atom.
Cesium-133 is ideal for this utility for just a few causes. It has one free electron in it is outermost power degree, which suggests it may be excited by a really particular and really common frequency. It will also be vaporized at low temperatures, which is required for the inside of the clock to work correctly.
When cesium-133 atoms are uncovered to microwaves of a really exact and constant frequency, they bear a predictable change in power ranges. The state of the atoms is detected contained in the clock, and whether or not or not they’re excited tells the clock if the microwave frequency is appropriate.
In less complicated phrases, atomic clocks don’t truly depend seconds, they create them. Within the case of cesium atomic clocks, this frequency is strictly 9,192,631,770 cycles per second – a resonant frequency of cesium-133. This exact measurement is so dependable that in 1967, the Worldwide System of Models (SI) redefined the second based mostly on this property of cesium-133.
By producing a relentless, measurable frequency that corresponds to the second, these gadgets guarantee international synchronization that impacts the whole lot out of your smartphone to the infrastructure that governs international navigation and communication. This degree of precision is not only about preserving correct time — it’s about making a framework upon which a lot of our fashionable expertise depends.
Timing and GNSS
Each GNSS satellite tv for pc has a number of on-board atomic clocks which might be preserving excellent time whereas making an allowance for the relativistic results they’re experiencing. Which means GNSS can present time along with latitude, longitude, and altitude.
Time can be how GNSS works – it makes use of what is known as trilateration to find out your location. It measures the time it takes for a sign to journey out of your location to a number of close by satellites. With out precise and synchronous time, exact positioning is not attainable.
The GNSS Disciplined Oscillator makes use of the time information from GNSS satellites to steer an ultra-precise quartz oscillator contained in the system, which might get accuracy beneath a nanosecond. GNSS has a pure decision of about 20 ns. At 5 ns, you begin to depend on your native oscillator to do additional filtering. With the GNSSDO, you are in a position to do that with excessive precision.
Measurements and Requirements
The Origin of Models
Hours, minutes, seconds… these items didn’t simply seem out of skinny air. The second existed earlier than we measured cesium on the atomic degree – now we have simply standardized it. The apply of dividing the times into segments was frequent within the historic world, and there have been many various programs in use for it. Historic Egyptians divided the night time and day into 12 segments every, which various in size with the altering of the seasons. They used a sundial to trace the daytime, then used a set of 12 stars within the night time sky to trace the passage of time in a single day.
Why 12? There are a number of theories for this, but it surely almost certainly was a mix of each. There are 12 lunar cycles in a 12 months, and you may also depend to 12 on one hand utilizing every finger joint of the 4 fingers. Making daytime and nighttime hours equal in period didn’t catch on till the 14th century.
What in regards to the smaller divisions of time? The Babylonians used a base 60 quantity system for astronomy, which is the place the minutes and seconds of astronomical diploma measurement come from, in addition to minutes and seconds of time. The quantity 60 is extraordinarily handy mathematically, divisible by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30. The phrase “minute” in latin means “first small half.” As you possibly can most likely guess, “second” means “second small half.” This conference caught on and is how we nonetheless measure not solely time, however levels.
Time Standardization
In all places on Earth has a neighborhood imply time, which is the photo voltaic time at a close-by meridian. When you’re just a few miles east of another person, technically you’re going to be midway by the Earth’s sunlight hours (what some might name midday) barely earlier than they’re. When you’re one diploma of latitude east of another person, you’ll see the solar rise 4 minutes earlier than they might. Till time zones had been launched within the nineteenth century, cities or cities stored their very own meridian time, which meant neighboring cities may have occasions that differed from one another by 4 minutes.
Most scientific developments all through American historical past boil all the way down to the navy or the railroad, and time zones aren’t any exception – this system-of-chaos time wasn’t good for the railroad. Whereas photo voltaic time continues to be used for astronomy and navigation, crossing nice distances on an everyday schedule with a number of stops wanted one thing extra streamlined.
Till 1883, every US railroad line selected its personal time customary, with telegraph workplaces alongside the strains receiving time alerts. Most strains from New York used New York time, most strains from Chicago used Chicago time, and all of the rail strains throughout the continent had been loyal to totally different time requirements. This was complicated.
In 1870, trainer Charles F. Dowd proposed time zones throughout the North American continent, first based mostly off of a meridian by Washington D.C., then revised to work round Greenwich Imply Time. These proposed zones spanned 15 levels of longitude, which converts to an hour (sound acquainted? timezones!).
A corporation of railroad management agreed to his proposal, and on Sunday, November 18, 1883, all United States and Canadian railroads would readjust their clocks and watches to replicate the brand new five-zone system on a telegraph sign from the Allegheny Observatory in Pittsburgh at precisely midday on the ninetieth meridian.
Dowd was actually form of only a man, so that is an inspirational story of the on a regular basis individual working to make infrastructure higher and making their concepts heard. Customary time didn’t exist in US legislation till 1918, which suggests it was clearly extra urgent of a problem than the constitutional modification that allowed some ladies to vote (1919). Ha.
Coordinated Common Time (UTC) is a globally standardized system that describes the offset of every area or zone’s photo voltaic time to the meridian that passes by Greenwich, England (GMT). This meridian was chosen on the Worldwide Meridian Convention of 1883 (oh, to be a fly on the wall!).
UTC relies on a weighted common of lots of of atomic clocks worldwide, and is inside about one second of imply photo voltaic time at 0° longitude. UTC is used because the worldwide customary for scientific use as properly, so issues like astronomical observations or time stamps on GPS transmissions are in UTC (and will be transformed to native time with software program).
Timekeeping Corrections
We’ve clearly performed lots of work ensuring time is measured as precisely as attainable, however there are issues we have now to account for and modifications we have to make to our definition and estimation of time to account for brand spanking new discoveries and inaccuracies.
Bissextile year occurs as soon as each 4 years (besides on years divisible by 100, except they’re additionally divisible by 400, for some cause), and exists as a result of our orbit across the solar isn’t precisely three hundred and sixty five days. The astronomical 12 months is rather less than 365.25 days, so if we add a day each 4 years we are able to keep on observe with our planet’s orbit.
Equally, leap seconds are single seconds sometimes added to UTC time to account for discrepancies between noticed photo voltaic time and Worldwide Atomic Time. The leap second was first launched in 1972. Since then, 27 leap seconds have been added to UTC, the newest occurring on December 31, 2016. All have to date been optimistic leap seconds, including a second to the tip of a UTC day. The Earth’s rotational velocity varies in response to climatic and geological occasions, so UTC leap seconds aren’t spaced usually and might’t be predicted. Including a leap second is often determined about six months beforehand by the Worldwide Earth Rotation and Reference Techniques Service (IERS). One other enjoyable acronym!
GPS satellites additionally must appropriate for relativistic results on time – each as a result of velocity and gravity. A clock in movement will tick extra slowly than one at relaxation, as will a clock nearer to a big physique of mass. With each particular and basic relativistic dilation collectively, GPS clocks expertise about 38 additional microseconds a day – not a lot, however that’ll add up. With out correcting this, GPS place information errors of 11km per day may accumulate.
To maintain time correctly for an on-Earth reference body, the frequency of the satellite tv for pc clocks is about decrease by 0.0045674 Hz in what’s known as “manufacturing unit offset”, the place the frequency of a satellite tv for pc clock is about to 10.22999999543 MHz so that it’ll tick in orbit on the identical fee as a ten.23 MHz atomic customary at sea degree on Earth.
Who Retains Time?
This can be a lot of data to maintain observe of. So, who manages these items?
As talked about above, the Worldwide Earth Rotation and Reference Techniques Service (IERS) controls the worldwide coordination of time by measuring photo voltaic time and mixing it with Worldwide Atomic Time to create UTC. The IERS tries to maintain UTC and Common Time inside 0.9 seconds of one another.
The U.S. Division of Transportation (DOT) oversees the USA’ time zones and Daylight Saving Time. The DOT’s secretary of transportation, in coordination with the states, determines which areas observe which period zones and in the event that they observe Daylight Saving Time.
The Nationwide Institute of Requirements and Know-how (NIST) is answerable for sustaining the USA’ official time in coordination with the U.S. Naval Observatory. NIST does this by constructing and working the nation’s most correct atomic clocks, which assist set UTC. NIST then gives time to the nation and the world by way of the web and radio. When you’ve got a watch that claims it is an atomic clock, extra doubtless than not it is simply getting the radio sign of the present time despatched out from NIST.
