An atomic clock is a clock device that uses an electron 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 and frequency standards known, and are used as primary standards for international time distribution services, to control the wave frequency of television broadcasts, and in global navigation satellite systems such as GPS.
The principle of operation of an atomic clock is based on atomic physics; it uses the microwave signal that electrons in atoms emit when they change energy levels. Early atomic clocks were based on masers at room temperature. Currently, the most accurate atomic clocks first cool the atoms to near absolute zero temperature by slowing them with lasers and probing them in atomic fountains in a microwave-filled cavity. An example of this is the NIST-F1 atomic clock, one of the national primary time and frequency standards of the United States.
The accuracy of an atomic clock depends on two factors. The first factor is temperature of the sample atoms—colder atoms move much more slowly, allowing longer probe times. The second factor is the frequency and intrinsic width of the electronic transition. Higher frequencies and narrow lines increase the precision.
National standards agencies in many countries maintain a network of atomic clocks which are intercompared and kept synchronized to an accuracy of 10−9 seconds per day (approximately 1 part in 1014). These clocks collectively define a continuous and stable time scale, the International Atomic Time (TAI). For civil time, another time scale is disseminated, Coordinated Universal Time (UTC). UTC is derived from TAI, but has added leap seconds from UT1, to account for the rotation of the Earth with respect to the solar time.
The idea of using atomic transitions to measure time was suggested by Lord Kelvin in 1879. Magnetic resonance, developed in the 1930s by Isidor Rabi, became the practical method for doing this. In 1945, Rabi first publicly suggested that atomic beam magnetic resonance might be used as the basis of a clock. The first atomic clock was an ammonia absorption line device at 23870.1 MHz built in 1949 at the U.S. National Bureau of Standards (NBS, now NIST). It was less accurate than existing quartz clocks, but served to demonstrate the concept. The first accurate atomic clock, a caesium standard based on a certain transition of the caesium-133 atom, was built by Louis Essen and Jack Parry in 1955 at the National Physical Laboratory in the UK. Calibration of the caesium standard atomic clock was carried out by the use of the astronomical time scale ephemeris time (ET). This led to the internationally agreed definition of the latest SI second being based on atomic time. Equality of the ET second with the (atomic clock) SI second has been verified to within 1 part in 1010. The SI second thus inherits the effect of decisions by the original designers of the ephemeris time scale, determining the length of the ET second.
Since the beginning of development in the 1950s, atomic clocks have been based on the hyperfine transitions in hydrogen-1, caesium-133, and rubidium-87. The first commercial atomic clock was the Atomichron, manufactured by the National Company. More than 50 were sold between 1956 and 1960. This bulky and expensive instrument was subsequently replaced by much smaller rack-mountable devices, such as the Hewlett-Packard model 5060 caesium frequency standard, released in 1964.
The Doomsday Clock is a symbol which represents the likelihood of a man-made global catastrophe. Maintained since 1947 by the members of the Bulletin of the Atomic Scientists’ Science and Security Board, the clock represents an analogy for the threat of global nuclear war. Since 2007, it has also reflected climate change and new developments in the life sciences and technology that could inflict irrevocable harm to humanity.
The clock represents the hypothetical global catastrophe as “midnight” and The Bulletin’s opinion on how close the world is to a global catastrophe as a number of “minutes” to midnight. Its original setting in 1947 was seven minutes to midnight. It has been set backward and forward 23 times since then, the smallest-ever number of minutes to midnight being two (in 1953 and 2018) and the largest seventeen (in 1991). As of January 2018, the clock is set at two minutes to midnight, due to “the looming threats of nuclear war and climate change.”
The Doomsday Clock’s origin can be traced to the international group of researchers called the Chicago Atomic Scientists, who had participated in the Manhattan Project. After the atomic bombings of Hiroshima and Nagasaki, they began publishing a mimeographed newsletter and then the magazine, Bulletin of the Atomic Scientists, which, since its inception, has depicted the clock on every cover. The clock was first represented in 1947, when The Bulletin co-founder Hyman Goldsmith asked artist Martyl Langsdorf (wife of Manhattan Project research associate and Szilárd petition signatory Alexander Langsdorf, Jr.) to design a cover for the magazine’s June 1947 issue. As Eugene Rabinowitch, another co-founder of The Bulletin, explained later,The Bulletin’s clock is not a gauge to register the ups and downs of the international power struggle; it is intended to reflect basic changes in the level of continuous danger in which mankind lives in the nuclear age…
Langsdorf chose a clock to reflect the urgency of the problem: like a countdown, the clock suggests that destruction will naturally occur unless someone takes action to stop it.In January 2007, designer Michael Bierut, who was on The Bulletin’s Governing Board, redesigned the clock to give it a more modern feel. In 2009, The Bulletin ceased its print edition and became one of the first print publications in the U.S. to become entirely digital; the clock is now found as part of the logo on The Bulletin’s website. Information about the Doomsday Clock Symposium, a timeline of the clock’s settings, and multimedia shows about the clock’s history and culture can also be found on The Bulletin’s website.
The 5th Doomsday Clock Symposium was held on November 14, 2013, in Washington, D.C.; it was a day-long event that was open to the public and featured panelists discussing various issues on the topic “Communicating Catastrophe”. There was also an evening event at the Hirshhorn Museum and Sculpture Garden in conjunction with the Hirshhorn’s current exhibit, “Damage Control: Art and Destruction Since 1950”. The panel discussions, held at the American Association for the Advancement of Science, were streamed live from The Bulletin’s website and can still be viewed there. Reflecting international events dangerous to humankind, the clock has been adjusted 22 times since its inception in 1947, when it was set to “seven minutes to midnight”.
A digital clock is a type of clock that displays the time digitally (i.e. in numerals or other symbols), as opposed to an analog clock, where the time is indicated by the positions of rotating hands.
Digital clocks are often associated with electronic drives, but the “digital” description refers only to the display, not to the drive mechanism. (Both analog and digital clocks can be driven either mechanically or electronically, but “clockwork” mechanisms with digital displays are rare.)
The first digital pocket watch was the invention of Austrian engineer Josef Pallweber who created his “jump-hour” mechanism in 1883. Instead of a conventional dial, the jump-hour featured two windows in an enamel dial, through which the hours and minutes are visible on rotating discs. The second hand remained conventional. By 1885 Pallweber mechanism was already on the market in pocket watches by Cortébert and IWC; arguably contributing to the subsequent rise and commercial success of IWC. The principles of Pallweber jump-hour movement had appeared in wristwatches by the 1920s (Cortébert) and are still used today (Chronoswiss Digiteur). While the original inventor didn’t have a watch brand at the time, his name has since been resurrected by a newly established watch manufacturer.
Plato clocks used a similar idea but a different layout. These spring-wound pieces consisted of a glass cylinder with a column inside, affixed to which were small digital cards with numbers printed on them, which flipped as time passed. The Plato clocks were introduced at the St. Louis World Fair in 1904, produced by Ansonia Clock Company. Eugene Fitch of New York patented the clock design in 1903. 13 years earlier Josef Pallweber had patented the same invention using digital cards (different from his 1885 patent using moving disks) in Germany (DRP No. 54093). The German factory Aktiengesellschaft für Uhrenfabrikation Lenzkirch made such digital clocks in 1893 and 1894.
The earliest patent for a digital alarm clock was registered by D.E Protzmann and others on October 23, 1956, in the United States. Protzmann and his associates also patented another digital clock in 1970, which was said to use a minimal amount of moving parts. Two side-plates held digital numerals between them, while an electric motor and cam gear outside controlled movement.
In 1970, the first digital wristwatch with an LED display was mass-produced. Called the Pulsar, and produced by the Hamilton Watch Company, this watch was hinted at two years prior when the same company created a prototype digital watch for Kubrick’s 2001: A Space Odyssey. Throughout the 1970s, despite the initial hefty cost of digital watches, the popularity of said devices steadily rose
Have you ever asked yourself ‘when will I die?’, our advanced life expectancy calculator will accurately* predict your death date for you depending on where you live, how much you smoke and your lifestyle to predict your own death clock.
To predict your death date, simply input your date of birth, sex, smoking habits, your BMI and the country you live in. If you don’t know your BMI simply click the link and our calculator will work out your BMI for you.
The Death Clock is the internet’s friendly reminder that life is slipping away, second by second.
To estimate the amount of seconds you have left to live, the site uses a handful of questions: Date of birth, gender, BMI (body mass index), smoking habits, and general outlook on life — that for some reason are categorized as pessimistic, optimistic, and sadistic. The Death Clock’s calculations are based on a study that estimated the expected number of years lost due to obesity across the lifespan of an adult.
Before finding out the rough date of your funeral, the tool asks for your BMI information emphasizing the dangers of excessive weight gain — as they so eloquently put it “The Lethal Danger of Being Fat.”
Answering the questions honestly, The Death Clock announced my “Personal Day of Death” to happen on Sunday, June 24 2091 — giving me 2,293,545,812 seconds of life (tick tock, tick tock.)
The 24-hour clock is the convention of time keeping in which the day runs from midnight to midnight and is divided into 24 hours, indicated by the hours passed since midnight, from 0 to 23. This system is the most commonly used time notation in the world today, and is used by international standard ISO 8601.
A limited number of countries, particularly English-speaking, use the 12-hour clock, or a mixture of the 24- and 12-hour time systems. In countries where the 12-hour clock is still dominant, some professions prefer to use the 24-hour clock. For example, in the practice of medicine the 24-hour clock is generally used in documentation of care as it prevents any ambiguity as to when events occurred in a patient’s medical history. In the United States and a handful of other countries, it is popularly referred to as military time.
1.1 Midnight 00:00 and 24:00
1.2 Times after 24:00
1.3 Computer support
1.4 Military time
3 See also
5 External links
A Russian 24 hour watch for polar expeditions from 1969, made by Soviet watchmaker Raketa. Polar nights or days make it necessary to use a 24-hour scale instead of 12.
A time of day is written in the 24-hour notation in the form hh:mm (for example 01:23) or hh:mm:ss (for example, 01:23:45), where hh (00 to 23) is the number of full hours that have passed since midnight, mm (00 to 59) is the number of full minutes that have passed since the last full hour, and ss (00 to 59) is the number of seconds since the last full minute. In the case of a leap second, the value of ss may extend to 60. A leading zero is added for numbers under 10, but it is optional for the hours. The leading zero is very commonly used in computer applications, and always used when a specifications require it (for example, ISO 8601).
Where subsecond resolution is required, the seconds can be a decimal fraction; that is, the fractional part follows a decimal dot or comma, as in 01:23:45.678. The most commonly used separator symbol between hours, minutes and seconds is the colon, which is also the symbol used in ISO 8601. In the past, some European countries used the dot on the line as a separator, but most national standards on time notation have since then been changed to the international standard colon. In some contexts (including the U.S. military and some computer protocols), no separator is used and times are written as, for example, “2359”.
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