User:Marshallsumter/Radiation astronomy/Clocks

A clock or a timepiece is a device used to measure and indicate time.

The verge escapement made possible the first mechanical clocks around 1300 in Europe, which kept time with oscillating timekeepers like balance wheels.

Theory of clocks
Def. the "study that relates with [of time, and] the art, science and technology of timekeeping or [and] timekeepers (e.g. [such as] a clock [clocks], watches or [and] sundial[s] )" is called horology.

Def. an "instrument used to measure or keep [that measures or keeps] track of time; a non-wearable timepiece" or "an electrical signal that synchronizes timing among digital circuits of semiconductor chips or modules" is called a clock.

Atomic clocks
A key value on the time axis for collecting physical data is the starting time. “Incandescents reach full brightness a fraction of a second after being switched on.”

An atomic clock is a clock device that uses an electronic transition frequency in the microwave, optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element. Atomic clocks are the most accurate time standard and frequency standards known, and are used as primary standards for international Time dissemination (time distribution services), to control the wave frequency of television broadcasts, and in global navigation satellite systems such as GPS.

The FOCS 1 continuous cold cesium fountain atomic clock started operating in 2004 at an uncertainty of one second in 30 million years. The clock is in Switzerland.

Clock drives
"[A] Clock drive is a regulatory mechanism used to move an equatorial mounted telescope along one axis of rotation to keep the telescope in exact sync with the apparent motion of the celestial sky diurnal motion"

Clock drives work by rotating a telescope mount's polar axis, the axis parallel to the Earth's polar axis (also called the right ascension axis) in the opposite direction to the Earth's rotation one revolution every 23 hours and 56 minutes (called sidereal day), thereby canceling that motion. This allows the telescope to stay fixed on a certain point in the sky without having to be constantly re-aimed due to the Earth's rotation. The mechanism itself used to be clockwork but nowadays is usually electrically driven. Clock drives can be light and portable for smaller telescopes or can be exceedingly heavy and complex for larger ones such as the 60 inch telescope at the Mount Wilson Observatory. Clock-driven equatorial platforms are sometimes used in non-tracking type mounts, such are altazimuth mounts.

Electric clocks
In 1814, Sir Francis Ronalds of London invented the first electric clock. It was powered with dry piles, a high voltage battery with Oxford Electric Bell (extremely long life) but the disadvantage of its electrical properties varying with the weather. He trialled various means of regulating the electricity and these models proved to be reliable across a range of meteorological conditions.

The first synchronous electric clock, MA, kept time from the oscillations of the power grid.

Precision regulator clock in the image second down on the right with electromagnetically-driven pendulum, is by Alexander Bain, London, around 1845 (Deutsches Uhrenmuseum [German clock museum], Inventory No. 2004-162). One of the first electric clocks ever built. The pendulum was kept swinging by pulses of magnetic force from an electromagnet (solenoid) (visible, bottom) near the bob, powered by a battery, and controlled by switch contacts (visible, center) on the pendulum rod.

A synchronous electric clock does not contain a timekeeping oscillator such as a pendulum or balance wheel, but instead counts the oscillations of the AC utility current from its wall plug to keep time, with a small AC synchronous motor, which turns the clock's hands through a reduction gear train. The motor contains electromagnets which create a rotating magnetic field which turns an iron rotor, where the rotation rate of the motor shaft is synchronized to the utility frequency; 60 cycles per second (Hz) in North America and parts of South America, 50 cycles per second in most other countries and the gear train scales this rotation so the minute hand rotates once per hour; thus the synchronous clock can be regarded as not so much a timekeeper as a mechanical counter, whose hands display a running count of the number of cycles of alternating current.

The accuracy of synchronous clocks depends on how close electric utilities keep the frequency of their current to the nominal value of 50 or 60 hertz, although utility load variations cause frequency fluctuations which may result in errors of a few seconds during the course of a day, utilities periodically adjust the frequency of their current using UTC atomic clock time so that the total number of cycles in a day gives an average frequency that is exactly the nominal value, so synchronous clocks do not accumulate error. For example, European utilities control the frequency of their grid once a day to make the total number of cycles in 24 hours correct. U.S. utilities correct their frequency once the cumulative error has reached 3–10 sec, where this correction is known as the Time Error Correction (TEC).

In the graph at bottom left, the shaded areas indicate periods of Daylight Savings Time.

GoTo mount drives
In amateur astronomy, "GoTo" refers to a type of telescope mount and related software which can automatically point a telescope to astronomical objects that the user selects. Both axes of a GoTo mount are motor driven and are controlled by either a microprocessor-based integrated controller or a personal computer, as opposed to the single axis semi-automated tracking of a traditional clock drive mount. This allows the user to command the mount to point the telescope to a right ascension and declination that the user inputs or have the mount itself point the telescope to objects in a pre-programmed data base including ones from the Messier catalogue, the New General Catalogue, and even major solar system bodies (the Sun, Moon, and planets).

Sheppard Gate Clock
The Shepherd Gate Clock (51.47793°N, -0.00141°W) is mounted on the wall outside the gate of the Royal Observatory, Greenwich, building in Greenwich, Greater London.

The system was first developed for the 1851 Great Exhibition (aka the Crystal Palace Exhibition in London), which lead the installation of a Shepherd Master and Slave clock system at the observatory. The time comes from the Shepherd Master Clock inside the observatory. In 1866 the time signal from the Shepherd Master Clock were sent across the Atlantic via cable to America.

The master clock, at first called the Normal Clock or Master Clock, but later known as the Mean Solar Standard Clock, sent pulses every second to sympathetic or slave clocks in the Chronometer Room, the Dwelling House (Flamsteed House), and at the gate (the Gate Clock).

From 1866 time signals were also sent to US Harvard University via the new transatlantic submarine cable.

The function of the Shepherd master clock:

This clock keeps in motion a sympathetic galvanic clock in the Chronometer room, which, therefore, is sensibly correct; and thus the chronometers are compared with a clock which requires no numerical correction.

The same Normal Clock maintains in sympathetic movement the large clock at the entrance-gate, two other clocks in the Observatory, and a clock at the London Bridge Terminus of the South-Eastern Railway.

It sends galvanic signals every day along all the principal railways diverging from London. It drops the Greenwich Ball and the Ball on the Offices of the Eastern Telegraph Company in the Strand.

All these various effects are produced without sensible error of time; and I cannot but feel a satisfaction in thinking that the Royal Observatory is thus quietly contributing to the punctuality of business through a large portion of this busy country.

Shortt–Synchronome clocks
The Shortt–Synchronome clock in the image on the right was purchased in 1929 and used in physicist Paul R. Heyl's measurement of the gravitational constant. On the left is the primary pendulum in its vacuum tank.

The Shortt–Synchronome free pendulum clock was a complex precision electromechanical pendulum clock invented in 1921 by British railway engineer William Hamilton Shortt in collaboration with horologist Frank Hope-Jones, and manufactured by the Synchronome Co., Ltd. of London, UK. They were the most accurate pendulum clocks ever commercially produced, and became the highest standard for timekeeping between the 1920s and the 1940s, after which mechanical clocks were superseded by quartz time standards. They were used worldwide in astronomical observatories, naval observatories, in scientific research, and as a primary standard for national time dissemination services. The Shortt was the first clock to be a more accurate timekeeper than the Earth itself; it was used in 1926 to detect tiny seasonal changes in the Earth's rotation rate. Shortt clocks achieved accuracy of around a second per year, although a recent measurement indicated they were even more accurate, where about 100 were produced between 1922 and 1956.

Sundials
The image at right shows a sun dial from Ai Khanoum, Afghanistan, dated to the 3rd century BCE, ~2300 b2k. The image at left is also from Ai Khanoum, Afghanistan, showing its workings.

"[T]he earliest known sundial [is] from an Egyptian burial dated in the fifteenth century B.C. Sometimes called a shadow clock, or an L-board because of its shape [with] relatively crude performance." A "[f]ragment of a late Egyptian sundial [from] about 3000 B.C." exists.

Time balls
The first time ball was erected at Portsmouth, England, in 1829 by its inventor Robert Wauchope, a captain in the Royal Navy. Others followed in the major ports of the United Kingdom (including Liverpool) and around the maritime world. One was installed in 1833 at the Royal Observatory, Greenwich in London by the Astronomer Royal, John Pond, originally to enable tall ships in the Thames to set their marine chronometers, and the time ball has dropped at 1 p.m. every day since then. Wauchope submitted his scheme to American and French ambassadors when they visited England. The United States Naval Observatory was established in Washington, D.C., and the first American time ball went into service in 1845.

Time balls were usually dropped at 1 p.m. (although in the United States they were dropped at noon), raised half way about 5 minutes earlier to alert the ships, then with 2–3 minutes to go they were raised the whole way, with the time recorded when the ball began descending, not when it reached the bottom.

With the commencement of radio time signals (in Britain from 1924), time balls gradually became obsolete and many were demolished in the 1920s.

Verge escapements
Def. the "spindle of a watch balance, especially one with pallets, as in the old vertical escapement" is called a verge.

Def. the "contrivance in a timepiece (winding wristwatch) which connects the train of wheel work with the pendulum or balance, giving to the latter the impulse by which it is kept in vibration" is called an escapement.

The verge escapement consists of a wheel shaped like a crown, called the escape wheel, with sawtooth-shaped teeth protruding axially toward the front, and with its axis oriented horizontally. In front of it is a vertical rod, the verge, with two metal plates, the pallets, that engage the teeth of the escape wheel at opposite sides. The pallets are not parallel, but are oriented with an angle in between them so only one catches the teeth at a time. Attached to the verge at its top is an inertial oscillator, a balance wheel or in the earliest clocks a foliot, a horizontal beam with weights on either end. This is the timekeeper of the clock.

The verge (or crown wheel) escapement is the earliest known type of mechanical escapement, the mechanism in a mechanical clock that controls its rate by allowing the gear train to advance at regular intervals or 'ticks', origin is unknown, used from the late 13th century until the mid 19th century in clocks and pocketwatches, from the Latin virga, meaning stick or rod.

Its invention is important in the history of technology, because it made possible the development of all-mechanical clocks which caused a shift from measuring time by continuous processes, such as the flow of liquid in water clocks, to repetitive, oscillatory processes, such as the swing of pendulums, which had the potential to be more accurate. Oscillating timekeepers are used in all modern timepieces.



The verge escapement dates from 13th-century Europe, where its invention led to the development of the first all-mechanical clocks. Starting in the 13th century, large tower clocks were built in European town squares, cathedrals, and monasteries. They kept time by using the verge escapement to drive a foliot, a primitive type of balance wheel. The foliot was a horizontal bar with weights near its ends affixed to a vertical bar called the verge which was suspended free to rotate. The verge escapement caused the foliot to oscillate back and forth about its vertical axis. The rate of the clock could be adjusted by moving the weights in or out on the foliot.

The verge escapement probably evolved from the alarum, which used the same mechanism to ring a bell and had appeared centuries earlier. There has been speculation that Villard de Honnecourt invented the verge escapement in 1237 with an illustration of a strange mechanism to turn an angel statue to follow the sun with its finger, but the consensus is that this was not an escapement.

It is believed that sometime in the late 13th century the verge escapement mechanism was applied to tower clocks, creating the first mechanical escapement clock. In spite of the fact that these clocks were celebrated objects of civic pride which were written about at the time, it may never be known when the new escapement was first used. This is because it has proven difficult to distinguish from the meager written documentation which of these early tower clocks were mechanical, and which were water clocks; the same Latin word, horologe, was used for both. None of the original mechanisms have survived unaltered. Sources differ on which was the first clock 'known' to be mechanical, depending on which manuscript evidence they regard as conclusive. One candidate is the Dunstable Priory clock in Bedfordshire, England built in 1283, because accounts say it was installed above the rood screen, where it would be difficult to replenish the water needed for a water clock. Another is the clock built at the Palace of the Visconti, Milan, Italy, in 1335. Astronomer Robertus Anglicus wrote in 1271 that clockmakers were trying to invent an escapement, but hadn't been successful yet. However, there is agreement that mechanical clocks existed by the late 13th century.

The earliest description of an escapement, in Richard of Wallingford's 1327 manuscript Tractatus Horologii Astronomici on the clock he built at the Abbey of St. Albans, was not a verge, but a variation called a 'strob' escapement. It consisted of a pair of escape wheels on the same axle, with alternating radial teeth. The verge rod was suspended between them, with a short crosspiece that rotated first in one direction and then the other as the staggered teeth pushed past. Although no other example is known, it is possible that this design preceded the more usual verge in clocks.

For the first two hundred years or so of the mechanical clock's existence, the verge, with foliot or balance wheel, was the only escapement used in mechanical clocks. In the sixteenth century alternative escapements started to appear, but the verge remained the most used escapement for 350 years until mid-17th century advances in mechanics, resulted in the adoption of the pendulum, and later the anchor escapement. Since clocks were valuable, after the invention of the pendulum many verge clocks were rebuilt to use this more accurate timekeeping technology, so very few of the early verge and foliot clocks have survived unaltered to the present day.

How accurate the first verge and foliot clocks were is debatable, with estimates of one to two hours error per day being mentioned, although modern experiments with clocks of this construction show accuracies of minutes per day were achievable with enough care in design and maintenance. Early verge clocks were probably no more accurate than the previous water clocks, but they did not require water to be manually hauled to fill the reservoir, did not freeze in winter, and were a more promising technology for innovation. By the mid-17th century, when the pendulum replaced the foliot, the best verge and foliot clocks had achieved an accuracy of 15 minutes per day.

Most of the gross inaccuracy of the early verge and foliot clocks was not due to the escapement itself, but to the balance wheel (foliot) oscillator. The first use of pendulums in clocks around 1656 suddenly increased the accuracy of the verge clock from hours a day to minutes a day. Most clocks were rebuilt with their foliots replaced by pendulums, to the extent that it is difficult to find original verge and foliot clocks intact today. A similar increase in accuracy in verge watches followed the introduction of the balance spring in 1658.



As the clock's gears turn the crown wheel (see animation), one of its teeth catches on a pallet, pushing on it. This rotates the verge and foliot in one direction, and rotates the second pallet into the path of the teeth on the opposite side of the wheel, until the tooth slides off the end of the pallet, releasing it. Then the crown wheel rotates freely a short distance until a tooth on the wheel's opposite side contacts the second pallet, pushing on it. This reverses the direction of the verge rod and foliot, rotating the verge back the other direction, until this tooth pushes past the second pallet. Then the cycle repeats. The result is to change the rotary motion of the wheel to an oscillating motion of the verge and foliot. Each swing of the balance wheel thus allows one tooth of the escape wheel to pass, advancing the wheel train of the clock by a fixed amount, moving the hands forward at a constant rate. The moment of inertia of the foliot or balance wheel controls the oscillation rate, determining the rate of the clock. The escape wheel tooth, pushing against the pallet each swing, provides an impulse which replaces the energy lost by the foliot to friction, keeping it oscillating back and forth.

In a verge pendulum clock (see picture) which appeared after the pendulum was invented in 1656, the escapement was turned 90° so the verge rod was horizontal, while the escape wheel's axis was vertical, located under the verge rod. In the first pendulum clocks the pendulum was attached to the end of the verge rod instead of the balance wheel or foliot. In later pendulum clocks the pendulum was suspended by a short straight spring of metal ribbon from the clock frame, and a vertical arm attached to the end of the verge rod ended in a fork which embraced the pendulum rod; this avoided the friction of suspending the pendulum directly from the pivoted verge rod. Each swing of the pendulum released an escape wheel tooth.

The escape wheel must have an odd number of teeth for the escapement to function. With an even number, two opposing teeth will contact the pallets at the same time, jamming the escapement. The usual angle between the pallets was 90° to 105°, resulting in a foliot or pendulum swing of around 80° to 100°. In order to reduce the pendulum's swing to make it more isochronous, the French used larger pallet angles, upward of 115°. This reduced the pendulum swing to around 50° and reduced recoil (below), but required the verge to be located so near the crown wheel that the teeth fell on the pallets very near the axis, reducing initial leverage and increasing friction, thus requiring lighter pendulums.

As might be expected from its early invention, the verge is the most inaccurate of the widely used escapements. It suffers from these problems:
 * Verge watches and clocks are sensitive to changes in the drive force; they slow down as the mainspring unwinds. This is called lack of isochronism. It was much worse in verge and foliot clocks due to the lack of a balance spring, but is a problem in all verge movements. In fact, the standard method of adjusting the rate of early verge watches was to alter the force of the mainspring. The cause of this problem is that the crown wheel teeth are always pushing on the pallets, driving the pendulum or balance wheel throughout its cycle; the timekeeping element is never allowed to swing freely. Thus a decreasing drive force causes the pendulum or balance wheel to swing back and forth more slowly. All verge watches and spring driven clocks required fusees to equalize the force of the mainspring to achieve even minimal accuracy.
 * The escapement has "recoil", meaning that the momentum of the foliot or pendulum pushes the crown wheel backward momentarily, causing the clock's wheel train to move backward, during part of its cycle. This increases friction and wear, resulting in inaccuracy. One way to tell whether an antique watch has a verge escapement is to observe the second hand closely; if it moves backward a little during each cycle, the watch is a verge. This is not necessarily the case in clocks, as there are some other pendulum escapements which exhibit recoil.
 * In pendulum clocks, the wide pendulum swing angles of 80°-100° required by the verge cause an additional lack of isochronism due to circular error.
 * The wide pendulum swings also cause a lot of air friction, reducing the accuracy of the pendulum, and requiring a lot of power to keep it going, increasing wear. So verge pendulum clocks had lighter bobs, which reduced accuracy.
 * Verge timepieces tend to accelerate as the crown wheel and the pallets wear down. This is particularly evident in verge watches from the mid-18th century onward. It is not in the least unusual for these watches, when run today, to gain many hours per day, or to simply spin as if there were no balance present. The reason for this is that as new escapements were invented, it became the fashion to have a thin watch. To achieve this in a verge watch requires the crown wheel to be made very small, magnifying the effects of wear.



Verge escapements were used in virtually all clocks and watches for 400 years. Then the increase in accuracy due to the introduction of the pendulum and balance spring in the mid 17th century focused attention on error caused by the escapement. By the 1820s, the verge was superseded by better escapements, though inexpensive verge watches continued to be made through the 19th century.

In pocketwatches, besides its inaccuracy, the vertical orientation of the crown wheel and the need for a bulky fusee made the verge movement unfashionably thick. French watchmakers adopted the thinner cylinder escapement, invented in 1695. In England, high end watches went to the duplex escapement, developed in 1782, but relatively inexpensive verge fusee watches continued to be produced until the mid 19th century, when the lever escapement took over. These later verge watches were colloquially called 'turnips' because of their bulky build.

The verge was only used briefly in pendulum clocks before it was replaced by the anchor escapement, invented around 1660 probably by Robert Hooke, and widely used beginning in 1680. The problem with the verge was that it required the pendulum to swing in a wide arc of 80° to 100°. Christiaan Huygens in 1674 showed that a pendulum swinging in a wide arc is an inaccurate timekeeper, because its period of swing is sensitive to small changes in the drive force provided by the clock mechanism.

Although the verge is not known for accuracy, it is capable of it. The first successful marine chronometers, H4 and H5, made by John Harrison in 1759 and 1770, used verge escapements with diamond pallets., In trials they were accurate to within a fifth of a second per day.

Today the verge is seen only in antique or antique-replica timepieces. Many original bracket clocks have their Victorian-era anchor escapement conversions undone and the original style of verge escapement restored. Clockmakers call this a verge reconversion.

Hypotheses

 * 1) Observers have been watching the skies and recording what they saw for more than 40,000 years.