atomic clock

One sort of public time signal is, of course, a striking clock. These clocks, however, are only as good as the clockwork that activates them; they have improved substantially since the first surviving clocks from the fourteenth century. For many members of the general public, a public clock such as Big Ben was the only time standard they needed. When more accurate public time signals were desired for use in navigation, a number of traditional audible or visible time signals were established for the purpose of allowing navigators to set their chronometers by. These publi ...

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Time signal, Time signal - Audible and visible time signals, Time signal - Electrical and electronic time signals, Time signal - Reference

Read more here: » Time signal: Encyclopedia II - Time signal - Audible and visible time signals

In the era when national broadcasting networks operated over point-to-point terrestrial microwave links, the time announcements were very accurate. Today, however, satellite and digital networks often have latencies on the order of a half second or a second. In places where a car radio can receive more than one station broadcasting the same national news program, when switching between them one often either misses part of a word or hears part of the same word twice due to such variations. Also, once upon a time every radio station had ...

See also:

Radio clock, Radio clock - Operation, Radio clock - Terrestrial time signals, Radio clock - Loran Clocks, Radio clock - GPS clocks, Radio clock - Other access

Read more here: » Radio clock: Encyclopedia II - Radio clock - Other access

The second (symbol: s) is the SI base unit of time. It is often abbreviated sec. in non-SI usage. Second - Definition. The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. Leap second, Orders of magnitude (time), UTC, Atomic clock Second - Origin. Originally, the second was known as a "second minute", ...

Including:

• Second - Definition
• Second - Origin
• Second - Conversions
• Second - Explanation

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The Hebrew calendar (Hebrew: הלוח העברי) or Jewish calendar is the annual calendar used in Judaism. It determines the dates of the Jewish holidays, the appropriate Torah portions for public reading, Yahrzeits (the date to commemorate the death of a relative), and the specific daily Psalms which some customarily read. Two major forms of the calendar have been used: an observational form used prior to the destruction of the Second Temple in 70, and based on witnesses observing ...

Including:

• Hebrew calendar - History
• Hebrew calendar - Biblical period
• Hebrew calendar - Babylonian exile
• Hebrew calendar - Second Temple era
• Hebrew calendar - Roman Era
• Hebrew calendar - Alexandrian Jewish calendar
• Hebrew calendar - Transition period
• Hebrew calendar - When does the year begin?
• Hebrew calendar - Modern calendar
• Hebrew calendar - Epoch
• Hebrew calendar - Measurement of the month
• Hebrew calendar - Pattern of calendar years
• Hebrew calendar - Measurement of hours
• Hebrew calendar - Measurement of lunar conjunctions/molads
• Hebrew calendar - Metonic cycle
• Hebrew calendar - Special holiday rules
• Hebrew calendar - Karaite interpretation
• Hebrew calendar - Accuracy

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A clock (from the Latin cloca, "bell") is an instrument for measuring time. A clock is usually a physical instrument; an especially accurate one is called a chronometer. The clock in its modern form (24 hour clock) has been in use since at least the 14th century. Clock can refer to an abstract system of time measurement (see calendar for other measurements). Modern clocks define constant units of time: an hour is always sixty minutes, of sixty seconds each. Clock - History. The clock is one of the ol ...

Including:

• Clock - History
• Clock - Purposes
• Clock - Ideal clocks
• Clock - Navigation
• Clock - Types
• Clock - Analog clocks
• Clock - Digital clocks
• Clock - Modern clocks
• Clock - Specific types of clocks

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Radio clocks depend on time signal radio stations, which usually have the following attributes: they refer their broadcast frequency to the frequency standard they broadcast seconds 'pips' to identify the start of second intervals also broadcast time codes as a way of identifying seconds intervals they publish exact geographic references for each antenna, so the radio signal's time-of-flight can be estimated. A variety of frequencies helps reception no matter what the ionospheric weather. Radio ...

See also:

Radio clock, Radio clock - Operation, Radio clock - Terrestrial time signals, Radio clock - Loran Clocks, Radio clock - GPS clocks, Radio clock - Other access

Read more here: » Radio clock: Encyclopedia II - Radio clock - Operation

Celestial navigation, also known as astronavigation, is a position fixing technique that was the first system devised to help sailors locate themselves on a featureless ocean. Celestial navigation uses angular measurements (sights) between the horizon and a common celestial object. The Sun is most often measured. Skilled navigators can use the Moon, planets or one of 57 "navigational stars" that are described in nautical almanacs. Sights on the moon, planets and stars allow navigation to occur at night or when clouds obscure ot ...

Including:

• Celestial navigation - How it works
• Celestial navigation - Angular Measurement
• Celestial navigation - Practical Navigation
• Celestial navigation - Latitude
• Celestial navigation - Longitude
• Celestial navigation - Modern Celestial Navigation

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Braunschweig [ˈbraunʃvaik] (English Brunswick) is a city of 245,500 people (as of December 31, 2004), located in Lower Saxony, Germany. It is located north of the Harz mountains at the farthest navigable point of the Oker river, which connects to the North Sea via the rivers Aller and Weser. Braunschweig - History. The date and circumstances of the town's foundation are unknown. Tradition maintains that Braunschweig was created thr ...

Including:

• Braunschweig - History
• Braunschweig - Historical population
• Braunschweig - Sights
• Braunschweig - Miscellaneous

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Very Long Baseline Interferometry (VLBI) is a type of interferometry in which the data received at each antenna in the array is paired with timing information, usually from a local atomic clock, and then stored for later analysis on magnetic tape or hard disk. At that later time, the data are correlated with data from other antennas similarly recorded, to produce the resulting image. The resolution achievable using interferometry is proportional to the distance between the antennas furthest apart in the array. The VLBI technique enabl ...

Including:

• Very Long Baseline Interferometry - Space VLBI
• Very Long Baseline Interferometry - How VLBI Works

Read more here: » Very Long Baseline Interferometry: Encyclopedia - Very Long Baseline Interferometry

Many modern radio clocks use the GPS satellite positioning system to provide more accurate time than can be obtained from these terrestrial radio stations. These GPS clocks combine time estimates from multiple satellite atomic clocks with error estimates maintained by a network of ground stations. Because they compute the time and position simultaneously from readings from several sources, GPS clocks can automatically compensate for line-of-sight delay and many radio propagation defects, and can achieve sub-microsecond accuracy under ...

See also:

Radio clock, Radio clock - Operation, Radio clock - Terrestrial time signals, Radio clock - Loran Clocks, Radio clock - GPS clocks, Radio clock - Other access

Read more here: » Radio clock: Encyclopedia II - Radio clock - GPS clocks

Standard time came into existence in the United States on November 18, 1883. Earlier, on October 11, 1883, the General Time Convention, forerunner to the American Railway Association, approved a plan that divided the United States into several time zones. On that November day, the United States Naval Observatory telegraphed a signal that coordinated noon at Eastern standard time with 11 AM Central, 10 AM Mountain, and 9 AM Pacific standard time. A March, 1905 issue of The Techical World describes the role of the United States N ...

See also:

Time signal, Time signal - Audible and visible time signals, Time signal - Electrical and electronic time signals, Time signal - Reference

Read more here: » Time signal: Encyclopedia II - Time signal - Electrical and electronic time signals

Masers serve as high precision frequency references. These "atomic frequency standards" are one form of atomic clock. They are also used as electronic amplifiers in radio telescopes. Maser - Hydrogen maser. Today, the most important type of maser is the hydrogen maser which is currently used as an atomic frequency standard. Together with other types of atomic clocks, they constitute the "Temps Atomic International" or TAI. This is the international time scale, which is coordinated by the Bureau International ...

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Maser, Maser - History, Maser - Technology, Maser - Some common types of masers, Maser - Astrophysical Masers, Maser - Uses, Maser - Hydrogen maser, Maser - Terminology, Maser - Masers in science fiction

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On the planet Skaro, the renegade Time Lord known as the Master is put on trial by the Daleks, and executed. His last wish is for his remains to be returned to Gallifrey by his greatest enemy, the Doctor. In the TARDIS, the Seventh Doctor stows the urn containing the Master's remains in a container, locking it with his sonic screwdriver, then settles in for the trip back to the Time Lords' planet. As he relaxes, however, he does not see the container shake and shatter. A gelatinous slug-like creature oozes out of the container and ent ...

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Doctor Who 1996, Doctor Who 1996 - Synopsis, Doctor Who 1996 - Plot, Doctor Who 1996 - Notes, Doctor Who 1996 - Controversy, Doctor Who 1996 - Novelisation

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Interrupts originated as a way to avoid wasting the processors valuable time in polling loops, waiting for external events. Instead, an interrupt signals the processor when an event occurs, allowing the processor to process other work while the event is pending. Interrupts may be implemented in hardware as a distinct system with control lines, or they may be integrated into the memory subsystem. If implemented in hardware, a Programmable Interrupt Controller (PIC) or Advanced Programmable Interrupt Controller (APIC) is connected to bo ...

See also:

Interrupt, Interrupt - Overview, Interrupt - Typical uses

Read more here: » Interrupt: Encyclopedia II - Interrupt - Overview

"In 1981 Casio began designing a new kind of wristwatch, based on the "Triple Ten" concept: A minimum of 10 year battery life, 10 bar water resistance, and the ability to withstand the shock of a 10 meter freefall. This resulted in the "Gravity Shock" wristwatch, or G-shock series." [Source: Carlos Perez, Time-Zone, (August 2002)] Traditionally, G-Shock timekeeping displays were exclusively digital, intended to be sold at re ...

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G-Shock, G-Shock - History, G-Shock - Today, G-Shock - Models/Series

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Some well-known music-radio formats are Top 40, Freeform Rock and AOR (Album Oriented Rock). It turns out that most other stations (such as Rhythm & Blues) use a variation of one of these formats with a different playlist. The way stations advertise themselves is not standardized. Some critical interpretation is needed to recognize classic formulas in the midst of the commercial glitz. See List of music radio formats for further details, and note that there is a great deal of format evolution as music tastes a ...

See also:

Music radio, Music radio - How it works, Music radio - Cost of programming, Music radio - Commercial Radio, Music radio - Programming, Music radio - Types of program segment, Music radio - Programming by Time, Music radio - Music formats, Music radio - Top 40, Music radio - Freeform and progressive rock, Music radio - AOR Album-Oriented Rock, Music radio - Oldies Standards and Classic rock, Music radio - Classical pop easy-listening jazz dance, Music radio - Alternative and Modern Rock, Music radio - Country Music, Music radio - Urban Hip-Hop/R&B, Music radio - Public Radio formats, Music radio - Promotional usages, Music radio - Song picking, Music radio - Technology

Read more here: » Music radio: Encyclopedia II - Music radio - Music formats

An early predecessor were the ground based LORAN and Omega systems, which used terrestrial longwave radio transmitters instead of satellites. These systems broadcast a radio pulse from a known "master" location, followed by repeated pulses from a number of "slave" stations. The delay between the reception and sending of the signal at the slaves was carefully controlled, allowing the receivers to compare the delay between reception and the delay between sending. From this the di ...

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Satellite navigation system, Satellite navigation system - History and theory, Satellite navigation system - Civil and military uses, Satellite navigation system - Current and proposed satellite navigation systems, Satellite navigation system - GPS, Satellite navigation system - GLONASS, Satellite navigation system - Galileo, Satellite navigation system - EGNOS, Satellite navigation system - Beidou, Satellite navigation system - DORIS, Satellite navigation system - Topics to be covered

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Essen spent all his working life at the National Physical Laboratory but caused some embarrassment to his employers in (1971) when he published The Special Theory of Relativity: A Critical Analysis in which he questioned Einstein's theories. He retired in 1972 and died in Great Bookham, Surrey. ...

See also:

Louis Essen, Louis Essen - Early work, Louis Essen - The speed of light, Louis Essen - Atomic clocks, Louis Essen - Time standards, Louis Essen - Later life, Louis Essen - Honours

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In principle any conductor (wire) carrying an alternating current will radiate a radio signal. Thus a basic transmitter is just an oscillator connected directly to a wire antenna. Since transmitters require excellent frequency stability, there are usually several amplifier stages between oscillator and antenna. The intermediate amplifier stages prevent changes in the antenna circuit from affecting the frequency of the oscillator. Often the transmitter frequency is not the frequency produced by the oscillator, but one of its harmonics. ...

See also:

Transmitter, Transmitter - History, Transmitter - Electromagnetic concepts, Transmitter - Skin effect and waveguides, Transmitter - Cooling of final stages, Transmitter - Protection equipment, Transmitter - Building, Transmitter - Legal and Regulatory Aspects, Transmitter - Planning, Transmitter - Transmitters in Culture, Transmitter - Records, Transmitter - Broadcasting

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The clock is one of the oldest human inventions. In principle, it requires no more than some physical process which will proceed at a known rate, and a way to gauge how long that process has been continuing. As the seasons and the phases of the moon can be used to measure the passage of longer periods of time, shorter processes could be used to measure off hours and minutes. The sundial, which measures the time of day by the direction of shadows cast by the sun, was widely known in ancient times. Candles and sticks of incense which burn down at approximately predictable speeds have also been used as clocks. In an hourglass fine sand pours through a ...

See also:

Clock, Clock - History, Clock - Types, Clock - Analog clocks, Clock - Digital clocks, Clock - Purposes, Clock - Ideal clocks, Clock - Navigation, Clock - Modern clocks, Clock - Specific types of clocks

Read more here: » Clock: Encyclopedia II - Clock - History