How many seconds are in a year?
Year
In astronomy, the Julian year is a unit of time; it is defined as 365.25 days of exactly 86,400 seconds (SI base unit), totalling exactly 31,557,600 seconds in the Julian astronomical year.
Year
This differs from the above definition of 365.25 days by about 20 parts per million. The joint document says that definitions such as the Julian year "bear an inherent, pre-programmed obsolescence because of the variability of Earth’s orbital movement", but then proposes using the length of the tropical year as of 2000 AD (specified down to the millisecond), which suffers from the same problem. (The tropical year oscillates with time by more than a minute.)
Metre per second
The SI unit symbols are m·s, m s, m/s, or , sometimes (unofficially) abbreviated as . Where metres per second are several orders of magnitude too slow to be convenient, such as in astronomical measurements, velocities may be given in kilometres per second, where is 1000 metres per second, sometimes unofficially abbreviated as "kps".
February 29
Although most modern calendar years have 365 days, a complete revolution around the Sun (one solar year) takes approximately 365 days and 6 hours. An extra 24 hours thus accumulates every four years, requiring that an extra calendar day be added to align the calendar with the Sun's apparent position. Without the added day, in future years the seasons would occur later in the calendar, eventually leading to confusion about when to undertake activities dependent on weather, ecology, or hours of daylight.
Second
A time scale in which the seconds are not exactly equal to atomic seconds is UT1, a form of universal time. UT1 is defined by the rotation of the earth with respect to the sun, and does not contain any leap seconds. UT1 always differs from UTC by less than a second.
Inch per second
The inch per second is a unit of speed or velocity. It expresses the distance  in inches ("in") traveled or displaced, divided by time in seconds ("s", or "sec"). The equivalent SI unit is the metre per second.
Year and a day rule
A year and a day is a minimum incarceration sentence for felonies in many jurisdictions, and is one of the main features distinguishing felonies from misdemeanors. For some crimes, this is the minimum penalty, as traditionally in English-speaking, common law countries, misdemeanors may not entail a sentence of a year or more (hence, "eleven months and twenty-nine days") whereas felonies are traditionally punished by incarceration of over one year, hence "a year and a day." Furthermore, in many jurisdictions, prisoners are eligible for parole only if their sentences are longer than a year; by imposing a sentence of a year and a day, judges can offer defendants a chance at parole. In the United States federal system, only sentences exceeding one year allow prisoners to obtain early release for good time while incarcerated. As a result, a sentence of a year and a day can lead to less time served than a sentence of a year.
Jewish Talmudic Calendar
The Jewish Talmudic Calendar, in agreement with the Almagest and the writings of Kidinnu, assumes that a month is uniformly of the length of an average synodic month, taken as exactly 29 days (about 29.530594 days, which is less than half a second from the modern scientific estimate); it also assumes that a tropical year is exactly 12 times that, i.e. about 365.2468 days. Thus it overestimates the length of the tropical year (365.2422 days) by 0.0046 days (about 7 minutes) per year, or about one day in 216 years. This error is less than the Julian years (365.2500 days) make (0.0078 days/year, or one day in 128 years), but much more than what the Gregorian years (365.2425 days/year) make (0.0003 days/year, or one day in 3333 years).
Seconds pendulum
A seconds pendulum is a pendulum whose period is precisely two seconds; one second for a swing in one direction and one second for the return swing, a frequency of 1/2 Hz. A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position. When released, the restoring force combined with the pendulum's mass causes it to oscillate about the equilibrium position, swinging back and forth. The time for one complete cycle, a left swing and a right swing, is called the period. The period depends on the length of the pendulum, and also to a slight degree on its weight distribution (the moment of inertia about its own center of mass) and the amplitude (width) of the pendulum's swing.
Year
The Galactic year is the time it takes Earth's solar system to revolve once around the galactic center. It comprises roughly 230 million Earth years.
List of humorous units of measurement
The beard-second is a unit of length inspired by the light-year, but applicable to extremely short distances such as those in integrated circuits. The beard-second is defined as the length an average beard grows in one second. Kemp Bennett Kolb defines the distance as exactly 100 angstroms (10 nanometers). as does Nordling and Österman's "Physics Handbook". However, Google Calculator supports the beard-second for unit conversions using the value 5 nm.
Tidal acceleration
For the earth-sun system, this gives 1x10 meters per second, or 3 meters in 1 million years. This is a 1% increase in the earth-sun distance in half a billion years. The decrease in the earth orbital angular momentum is 2x10sec, or equivalently for a 1-year period, 1 second in 1 billion years.
Second
Multiples of seconds are usually counted in hours and minutes. Fractions of a second are usually counted in tenths or hundredths. In scientific work, small fractions of a second are counted in milliseconds (thousandths), microseconds (millionths), nanoseconds (billionths), and sometimes smaller units of a second.
An everyday experience with small fractions of a second is a 1-gigahertz microprocessor which has a cycle time of 1 nanosecond. Camera shutter speeds usually range from second to second.
Rotation period
Earth's rotation period relative to the fixed stars, called its "stellar day" by the International Earth Rotation and Reference Systems Service (IERS), is seconds of mean solar time (UT1) Earth's rotation period relative to the precessing or moving mean vernal equinox, its "sidereal day", is seconds of mean solar time (UT1) Thus the sidereal day is shorter than the stellar day by about 8.4 ms. The length of the mean solar day in SI seconds is available from the IERS for the periods 1623–2005 and 1962–2005.
Recently (1999–2005) the average annual length of the mean solar day in excess of 86400 SI seconds has varied between 0.3 ms and 1 ms, which must be added to both the stellar and sidereal days given in mean solar time above to obtain their lengths in SI seconds.
Second
Although the historical definition of the unit was based on this division of the Earth's rotation cycle, the formal definition in the International System of Units (SI) is a much steadier timekeeper: 1 second is defined to be exactly "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" (at a temperature of 0 K).
Because the Earth's rotation varies and is also slowing ever so slightly, a leap second is periodically added to clock time to keep clocks in sync with Earth's rotation.
Day
A day, a unit of time, is approximately the period of time during which the Earth completes one rotation around its axis with respect to the Sun ("solar day"). In 1960, the second was redefined in terms of the orbital motion of the Earth in year 1900, and was designated the SI base unit of time. The unit of measurement "day", was redefined as 86 400 SI seconds and symbolized "d". In 1967, the second and so the day were redefined by atomic electron transition. A civil day is usually 86 400 seconds, plus or minus a possible leap second in Coordinated Universal Time (UTC), and occasionally plus or minus an hour in those locations that change from or to daylight saving time.
Decimal time
In principle, time spans greater than one second are given in units such as kiloseconds (ks), myriasecond (mys), megaseconds (Ms), gigaseconds (Gs), and so on. (The myriasecond is based on the "myria-" prefix, which represented a multiple of 10000 but was made obsolete in the mid-20th century.) Occasionally, these units can be found in technical literature, but traditional units like minutes, hours, days and years are much more common, and are accepted for use with SI.
Words per minute
Research done in 2012 measured the speed at which subjects read a text aloud, and found the average speed across 17 different languages to be 184±29 wpm or 863±234 characters per minute. However, for the languages that use the Latin or Cyrillic alphabets, the number of wpm varied, as low as 161±18 for Finnish and as high as 228±30 for English. The reason for this is different word structures in each language (longer words in such languages as Finnish and shorter words in English). However, the number of characters per minute tends to be around 1000 for all the tested languages. For the tested Asian languages that use particular writing systems (Arabic, Hebrew, Chinese, Japanese) these numbers are lower.
Leap year
The length of a day is also occasionally changed by the insertion of leap seconds into Coordinated Universal Time (UTC), owing to the variability of Earth's rotational period. Unlike leap days, leap seconds are not introduced on a regular schedule, since the variability in the length of the day is not entirely predictable.
Astronomical unit
In 1983, the International Committee for Weights and Measures (CIPM) modified the International System of Units (SI, or "modern" metric system) to make the metre defined as the distance travelled in a vacuum by light in 1/299792458 second. This replaced the previous definition, valid between 1960 and 1983, which was that the metre equalled a certain number of wavelengths of a certain emission line of krypton-86. (The reason for the change was an improved method of measuring the speed of light.) The speed of light could then be expressed exactly as "c" = , a standard also adopted by the IERS numerical standards. From this definition and the 2009 IAU standard, the time for light to traverse an AU is found to be τ = , more than 8 minutes. By multiplication, the best IAU 2009 estimate was "A" = "c"τ = , based on a comparison of JPL and IAA–RAS ephemerides.
Minute
The minute is a unit of time or angle. As a unit of time, the minute is most of times equal to (the first sexagesimal fraction) of an hour, or 60 seconds. In the UTC time standard, a minute on rare occasions has 61 seconds, a consequence of leap seconds (there is a provision to insert a negative leap second, which would result in a 59-second minute, but this has never happened in more than 40 years under this system). As a unit of angle, the minute of arc is equal to of a degree, or 60 seconds (of arc). Although not an SI unit for either time or angle, the minute is accepted for use with SI units for both. The SI symbols for "minute" or "minutes" are min for time measurement, and the prime symbol after a number, e.g. 5′, for angle measurement. The prime is also sometimes used informally to denote minutes of time.
Uncertainty parameter
648 000 is the number of arc seconds in a half circle, so a value greater than 9 would mean that we would have basically no idea where the object will be in 10 years.
Year
The anomalistic year is the time taken for the Earth to complete one revolution with respect to its apsides. The orbit of the Earth is elliptical; the extreme points, called apsides, are the perihelion, where the Earth is closest to the Sun (January 3 in 2011), and the aphelion, where the Earth is farthest from the Sun (July 4 in 2011). The anomalistic year is usually defined as the time between perihelion passages. Its average duration is days (365 d 6 h 13 min 52.6 s) (at the epoch J2011.0).
Year
In the Unified Code for Units of Measure, the symbol, "a" (without subscript), always refers to the Julian year, "a", of exactly seconds.
Surya Siddhanta
The "Surya Siddhanta" calculates the solar year to be 365 days 6 hours 12 minutes and 36.56 seconds. On average, according to the text, the lunar month equals 27 days 7 hours 39 minutes 12.63 seconds. It states that the lunar month varies over time, and this needs to be factored in for accurate time keeping.
List of humorous units of measurement
According to Gian-Carlo Rota, the mathematician John von Neumann used the term microcentury to denote the maximum length of a lecture. One microcentury is 52 minutes and 35.7 seconds – one millionth of a century.
Minute and second of arc
A minute of arc, arcminute (arcmin), arc minute, or minute arc is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn – it is for this reason that the Earth's circumference is almost exactly 21,600 nautical miles. A minute of arc is of a radian.
Rotation period
Earth's rotation period relative to the Sun (its mean solar day) consists of 86,400 seconds of mean solar time, by definition. Each of these seconds is slightly longer than an SI second because Earth's solar day is now slightly longer than it was during the 19th century, due to tidal deceleration. The mean solar second between 1750 and 1892 was chosen in 1895 by Simon Newcomb as the independent unit of time in his Tables of the Sun. These tables were used to calculate the world's ephemerides between 1900 and 1983, so this second became known as the ephemeris second. The SI second was made equal to the ephemeris second in 1967.
Year
A calendar year is an approximation of the number of days of the Earth's orbital period as counted in a given calendar. The Gregorian calendar, or modern calendar, presents its calendar year to be either a common year of 365 days or a leap year of 366 days, as do the Julian calendars; "see" below. For the Gregorian calendar, the average length of the calendar year (the mean year) across the complete leap cycle of 400 years is 365.2425 days. The ISO standard ISO 80000-3, Annex C, supports the symbol "a" (for Latin "annus") to represent a year of either 365 or 366 days. In English, the abbreviations "y" and "yr" are commonly used.
Tropical year
The mean tropical year on January 1, 2000 was or 365 ephemeris days, 5 hours, 48 minutes, 45.19 seconds. This changes slowly; an expression suitable for calculating the length of a tropical year in ephemeris days, between 8000 BC and 12000 AD is
Hour
In the modern metric system, hours are an accepted unit of time equal to 3,600 seconds but an hour of Coordinated Universal Time (UTC) may incorporate a positive or negative leap second, making it last 3,599 or 3,601 seconds, in order to keep it within 0.9 seconds of universal time, which is based on measurements of the mean solar day at 0° longitude.
Time formatting and storage bugs
Certain problematic years occur so far in the future, well beyond the likely lifespan of the Earth, the Sun, humanity, and even past some predictions of the lifetime of the universe, that they are mainly referenced as matters of theoretical interest, jokes, or indications that a related problem is not truly solved for any reasonable definition of "solved".Note: these year values are based on an average year of exactly 365.2425 days, which matches the 4/100/400 leap year rules of the commonly used Gregorian calendar. Additional adjustments to the calendar over intervals this long are unavoidable, as the actual year is currently slightly shorter (about 365.242374 days) than assumed, the length of Earth's orbit around the Sun changes over time (tropical years are currently becoming shorter at a rate of about 0.53 seconds per century), and in any case, all of these times far exceed the likely existence of the Earth. So the year numbers should be considered approximate.
Oenopides
Oenopides put the Great Year at 59 years, corresponding to 730 months. This was a good approximation, but not a perfect one, since 59 (sidereal) years are equal to 21550.1 days, while 730 (synodical) months equal 21557.3 days. The difference therefore amounts to seven days. In addition there are the interfering variations in the lunar orbit. However, a 59-year period had the advantage that it corresponded quite closely to an integer number of orbital revolutions of several planets around the sun, which meant that their relative positions also repeated each Great Year cycle. Before Oenopides a Great Year of eight solar years was in use (= 99 months). Shortly after Oenopides, in 432 BC, Meton and Euctemon discovered the better value of 18 years, equal to 223 months (the so-called Saros period).
Year zero
All eras used with Hindu and Buddhist calendars, such as the Saka era or the Kali Yuga, begin with the year 0. All these calendars use elapsed, expired, or complete years, in contrast with most other calendars which use current years. A complete year had not yet elapsed for any date in the initial year of the epoch, thus the number 1 cannot be used. Instead, during the first year the indication of 0 years (elapsed) is given in order to show that the epoch is less than 1 year old. This is similar to the Western method of stating a person's age – people do not reach age one until one year has elapsed since birth (but their age during the year beginning at birth is specified in months or fractional years, not as age zero). However, if ages were specified in years and months, such a person would be said to be, for example, 0 years and 6 months or 0.5 years old. This is analogous to the way time is shown on a 24-hour clock: during the first hour of a day, the time elapsed is 0 hours, "n" minutes.
Tachymeter (watch)
where T is the tachymeter scale value; t is the time in seconds that it takes for the event to occur; and 3600 is the number of seconds in an hour.
As a sample calculation, if it takes 35 seconds to travel one mile, then the average speed is 103 miles/hour. On the watch, 35 seconds gives scale value 103. Similarly, if one kilometre takes 35 seconds then the average speed would be 103 km/hour.
Random password generator
In this case, the standard C function "rand", which is a pseudo-random number generator, is initially seeded using the C functions "time", but later iterations use "rand" instead. According to the ANSI C standard, "time" returns a value of type "time t", which is implementation defined, but most commonly a 32-bit integer containing the current number of seconds since January 1, 1970 ("see:" Unix time). There are about 31 million seconds in a year, so an attacker who knows the year (a simple matter in situations where frequent password changes are mandated by password policy) and the process ID that the password was generated with, faces a relatively small number, by cryptographic standards, of choices to test. If the attacker knows more accurately when the password was generated, he faces an even smaller number of candidates to test – a serious flaw in this implementation.
Cosmic year (Chinese astrology)
In anthroposophy, based on teachings by Rudolf Steiner, a cosmic year represents the Platonic year, a period of 25,920 years. This is the time required for the Sun's position at spring equinox to traverse the complete zodiac. So each zodiacal sign covers about 2160 years. The year 747 BCE marked the transition from Taurus to Aries and since 1453, the spring equinoctial sun is in Pisces. This cosmic cycle has a considerable influence on humanity in both physical and spiritual respects. For instance, the Aries period covered the Greek/Roman culture period ranging from the foundation of Rome (753 BCE) to the fall of Byzantium (1453), whereas the Taurus period marked the Egyptian/Chaldaean era. Another example is human breathing rhythm: an average of 18 cycles per minute represents 18 x 60 x 24 = 25,920 cycles per day. The number of daily sleep-wake-cycles of the conscious mind in an average human lifetime of 72 years adds up to the same platonic figure. Shao Yung's cosmic year represents exactly five platonic years (5x25,920=129,600).
Bubnoff unit
The Bubnoff unit (abbreviated B) is a unit of speed equal to 1 m / 10 a. In other words, 1 B is equal to 1 meter in 1,000,000 years, 1 millimeter in 1,000 years, or one micrometer per year. It was defined in 1969.
Millisecond
A millisecond (from milli- and second; symbol: ms) is a thousandth (0.001 or 10 or /) of a second.
Equation of time
During a year the equation of time varies as shown on the graph; its change from one year to the next is slight. Apparent time, and the sundial, can be ahead (fast) by as much as 16 min 33 s (around 3 November), or behind (slow) by as much as 14 min 6 s (around 12 February). The equation of time has zeros near 15 April, 13 June, 1 September and 25 December. Ignoring very slow changes in the Earth's orbit and rotation, these events are repeated at the same times every tropical year. However, due to the non-integer number of days in a year, these dates can vary by a day or so from year to year.
Astrological age
This means the Sun crosses the equator at the vernal equinox moving backwards against the fixed stars from one year to the next at the rate of one degree in seventy-two years, one constellation (on average) in about 2160 years, and the whole twelve signs in about 25,920 years, sometimes called a Platonic Year. However the length of the ages are decreasing with time as the rate of precession is increasing. Therefore, no two ages are of equal length.
Glasshouse (novel)
Kilosecond : 16 minutes
Metre per second
The metre per second (American English: meter per second) is an SI derived unit of both speed (scalar) and velocity (vector quantity which specifies both magnitude and a specific direction), defined by distance in metres divided by time in seconds.
Timeline of astronomy
The Hindu cosmological time cycles explained in the "Surya Siddhanta", give the average length of the sidereal year (the length of the Earth's revolution around the Sun) as 365.2563627 days, which is only 1.4 seconds longer than the modern value of 365.256363004 days. This remains the most accurate estimate for the length of the sidereal year anywhere in the world for over a thousand years.
Discworld (world)
The calendar is based on a Great Year, or Astronomical Year, defined as the time it takes for the Disc to revolve once on the backs of the elephants. This lasts 800 days and contains two of each season (Midsummer occurs at a given point when the sun passes directly overhead, midwinter when it passes perpendicularly. However most people, especially farmers, consider four seasons to be a year, so an Agricultural Year of 400 days is used for most purposes.
Yoruba people
Time is measured in "ìṣẹ́jú" (minutes), "wákàtí" (hours), "ọjọ́" (days), "ọ̀sẹ̀" (weeks), "oṣù" (months) and "ọdún" (years). There are 60 "ìṣẹ́jú" in 1 "wákàtí"; 24 "wákàtí" in 1 "ọjọ́"; 7 "ọjọ́" in 1 "ọ̀sẹ̀"; 4 "ọ̀sẹ̀" in 1 "oṣù" and 52 "ọ̀sẹ̀" in 1 "ọdún". There are 12 "oṣù" in 1 "ọdún".
The Yoruba week consist of five days. Of these, only four have names. Traditionally, the Yoruba count their week starting from the Ojó Ògún, this day is dedicated to Ògún. The second day is Ojó Jákúta the day is dedicated to Sàngó. The third day is known as the Ojó Òsè- this day is dedicated to Òrìshà ńlá (Obàtálá), while the fourth day is the Ojó Awo, in honour of Òrúnmìlà.
The Yoruba calendar (Kojoda) year starts from 3 June to 2 June of the following year. According to this calendar, the Gregorian year 2008 CE is the 10,050th year of Yoruba culture. To reconcile with the Gregorian calendar, Yoruba people also often measure time in seven days a week and four weeks a month:
Light-year
The light-year is a unit of length used to express astronomical distances and measures about 9.46 trillion kilometres (9.46 x 10 km) or 5.88 trillion miles (5.88 x 10 mi). As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Because it includes the word "year", the term light-year is sometimes misinterpreted as a unit of time.
List of unusual units of measurement
There have been numerous proposals and usage of decimal time, most of which were based on the day as the base unit. For instance, in dynastic China, the kè was a unit that represented of a day (it has since been refined to of a day, or 15 minutes). In France, a decimal time system in place from 1793 to 1805 divided the day into 10 hours, each divided into 100 minutes, in turn each divided into 100 seconds; the French Republican Calendar further extended this by assembling days into ten-day "weeks". Ordinal dates and Julian days, the latter of which has seen use in astronomy as it is not subject to leap year complications) allow for the expression of a decimal portion of the day. In the mid-1960s, to defeat the advantage of the recently introduced computers for the then popular rally racing in the Midwest, competition lag times in a few events were given in centids ( day, 864 seconds, 14.4 minutes), millids ( day, 86.4 seconds) and centims ( minute, 0.6 seconds) the latter two looking and sounding a bit like the related units of minutes and seconds. Decimal time proposals are frequently used in fiction, often in futuristic works.
Second
The second is the SI base unit of time, commonly understood and historically defined as of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each. Mechanical and electric clocks and watches usually have a face with 60 tickmarks representing seconds and minutes, traversed by a second hand and minute hand. Digital clocks and watches often have a two-digit counter that cycles through seconds. The second is also part of several other units of measurement like meters per second for velocity, meters per second per second for acceleration, and per second for frequency.
Mathematical coincidence
formula_24 seconds is a nano-century: 100 years × 365.25 days per year (0.25 is for a leap day every fourth year) × 24 hours per day × 3600 seconds per hour = 3,155,760,000 sec ≈ "π" sec × 10 within 0.45%.
Year 2038 problem
Alternative proposals have been made (some of which are in use), such as storing either milliseconds or microseconds since an epoch (typically either 1 January 1970 or 1 January 2000) in a signed 64-bit integer, providing a minimum range of 300,000 years at microsecond resolution. Other proposals for new time representations provide different precisions, ranges, and sizes (almost always wider than 32 bits), as well as solving other related problems, such as the handling of leap seconds. In particular, TAI64 is an implementation of the "Temps Atomique International" standard, the current international real-time standard for defining a second and frame of reference.
Axial precession
Hipparchus also studied precession in "On the Length of the Year". Two kinds of year are relevant to understanding his work. The tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). The sidereal year is the length of time that the Sun takes to return to the same position with respect to the stars of the celestial sphere. Precession causes the stars to change their longitude slightly each year, so the sidereal year is longer than the tropical year. Using observations of the equinoxes and solstices, Hipparchus found that the length of the tropical year was 365+1/4−1/300 days, or 365.24667 days (Evans 1998, p. 209). Comparing this with the length of the sidereal year, he calculated that the rate of precession was not less than 1° in a century. From this information, it is possible to calculate that his value for the sidereal year was 365+1/4+1/144 days (Toomer 1978, p. 218). By giving a minimum rate he may have been allowing for errors in observation.
Gregorian calendar
Calendar cycles repeat completely every 400 years, which equals 146,097 days. Of these 400 years, 303 are regular years of 365 days and 97 are leap years of 366 days. A mean calendar year is days = 365.2425 days, or 365 days, 5 hours, 49 minutes and 12 seconds.
Ephemeris day
An ephemeris day is a period of 86,400 SI seconds. The actual length of a solar day varies, and has a tendency to get longer as the tides slow the earth down (see Tidal acceleration). In the Système International (SI), the length of day during the late 19th century was used to define the second. (See ΔT.) In recent decades, the length of a solar day has usually been a couple of milliseconds more than an ephemeris day.
Cosmological decade
The cosmological decade can be expressed in log years per decade. In this definition, the 100th cosmological decade lasts from 10 years to 10 years after Time Zero. To convert to this format, simply divide by seconds per year; or in logarithmic terms, subtract 7.4991116 from the values listed above. Thus when CÐ is expressed in log( years/Ð ), the Planck time could also be expressed as 10 years = 10 years.
List of unusual units of measurement
George Gamow discussed measurements of time such as the "light-mile" and "light-foot", the time taken for light to travel the specified unit distance, defined by "reversing the procedure" used in defining a light-year. One light-nanosecond is roughly 30 centimeters (29.9792458 cm exactly), or about a foot (30.48 cm).
WWVB
The binary time code shows minute 0x064631A = 6578970 of the century. Dividing by 1440 minutes per day, this is minute 1050 (= 17×60 + 30) of day 4568 of the century. There are 365×12 + 3 = 4383 days in the 12 years before 2012, so this is day 185 of the year. This day number begins at 0 on January 1, rather than 1 like the BCD time code, so it encodes the same date.
Prophetic Year
Examples of use of the first definition:
Now this seventieth week is admittedly a period of seven years, and half of this period is three times described as "a time, times, and half a time," or "the dividing of times'"* twice as forty-two months;† and twice as 1,260 days.‡ But 1,260 days are exactly equal to forty-two months of thirty days, or three and a half years of 360 days, whereas three and a half Julian years contain 1,278 days. It follows therefore that the prophetic year is not the Julian year, but the ancient year of 360 days.§
(*) Dan. vii. 25; xii. 7; Rev. xii. 14.
† Rev. xi. 2' xiii. 5.
‡ Rev. xi. 3' xii. 6.
§ It is noteworthy that the prophecy was given at Babylon, and the Babylonian year consisted of twelve months of thirty days. That the prophetic year is not the ordinary year is no new discovery. It was noticed sixteen centuries ago by Julias Africanus in his "Chronography", wherein he explains the seventy weeks to be weeks of "Jewish" (lunar) years, beginning with the twentieth of Artaxerxes, the fourth year of the 83rd Olympiad, and ending in the second year of the 202nd Olympiad; 475 Julian years being equal to 490 lunar years.
The second and third definition can be said to follow from application of the day for a year principle.
Carnegie Unit and Student Hour
Per its original definition, the Carnegie Unit is 120 hours of class or contact time with an instructor over the course of a year at the secondary (American high school) level. Strictly speaking, this breaks down into a single one-hour meeting, on each of five days per week for a total of 24 weeks per year. However, knowing that classes usually meet for 50 minutes yields a value of 30 weeks per year. However, further complicating the computation is the fact that American schools typically meet 180 days, or 36 academic weeks, a year. A semester (one-half of a full year) earns 1/2 a Carnegie Unit.
Light-year
Distances between objects within a star system tend to be small fractions of a light year, and are usually expressed in astronomical units. However, smaller units of length can similarly be formed usefully by multiplying units of time by the speed of light. For example, the light-second, useful in astronomy, telecommunications and relativistic physics, is exactly metres or of a light-year. Units such as the light-minute, light-hour and light-day are sometimes used in popular science publications. The light-month, roughly one-twelfth of a light-year, is also used occasionally for approximate measures. The Hayden Planetarium specifies the light month more precisely as 30 days of light travel time.
Reeling In the Years
Each episode, running for about 25 minutes, reviews the events of a particular selected year, from 1962 to 2009. News archive footage features, along with subtitles as the means of narration, to recount important national and international events of the time. Music from the selected year plays across the footage, with occasional scenes of live performances or music videos, often (but by no means exclusively) by an Irish artist. No advertisements are shown during the broadcast (apart from the occasional old advertisement dating from the relevant year). Each decade takes at least eight months to make.
Unix time
Unix time is a single signed number which increments every second, without requiring the calculations to determine year, month, day of month, hour and minute required for intelligibility to humans.
Hipparchic cycle
The second is a calendar cycle: Hipparchus proposed a correction to the Calippic cycle (of 76 years), which itself was proposed as a correction to the Metonic cycle (of 19 years). He may have published it in the book "On the Length of the Year" (Περὶ ἐνιαυσίου μεγέθους), which is lost. From solstice observations, Hipparchus found that the tropical year is about of a day shorter than the days that Calippus used (see "Almagest" III.1). So he proposed to make a 1-day correction after 4 Calippic cycles, such that 304 years = 3760 lunations = 111035 days. This is a very decent approximation for an integer number of lunations in an integer number of days (error only 0.014 days). But it is in fact 1.37 days longer than 304 tropical years: the mean tropical year is actually about day (11 minutes 15 seconds) shorter than the Julian calendar year of days. These differences cannot be corrected with any cycle that is a multiple of the 19-year cycle of 235 lunations: it is an accumulation of the mismatch between years and months in the basic Metonic cycle, and the lunar months need to be shifted systematically by a day with respect to the solar year ("i.e." the Metonic cycle itself needs to be corrected) after every 228 years.
Indeed, from the values of the tropical year (365.2421896698 days) and the synodic month (29.530588853) cited in the respective articles of Wikipedia, it follows that the length of 228=12*19 tropical years is about 83275.22 days, shorter than the length of 12*235 synodic months, namely about 83276.26 days, by one day plus about one hour. In fact, an even better correction would be to correcting by two days every 437 years, rather than one day every 228 years. The length of 437=23*19 tropical years, about 159610.837 days, is shorter than that of 23*235 synodic months, about 159612.833 days, by almost exactly two days, up to only six minutes.
Mathematical coincidence
Another coincidence related to the gravitational acceleration "g" is that its value of approximately 9.8 m/s is equal to 1.03 light-year/year, which numerical value is close to 1. This is related to the fact that "g" is close to 10 in SI units (m/s), as mentioned above, combined with the fact that the number of seconds per year happens to be close to the numerical value of "c"/10, with "c" the speed of light in m/s. In fact, it has nothing to do with SI as "c/g" = 354 days, nearly, and 365/354 = 1.03.
Minute
Historically, the word "minute" comes from the Latin "pars minuta prima", meaning "first small part". This division of the hour can be further refined with a "second small part" (Latin: "pars minuta secunda"), and this is where the word "second" comes from. For even further refinement, the term "third" ( of a second) remains in some languages, for example Polish ("tercja") and Turkish ("salise"), although most modern usage subdivides seconds by using decimals. The symbol notation of the prime for minutes and double prime for seconds can be seen as indicating the first and second cut of the hour (similar to how the foot is the first cut of the yard or perhaps chain, with inches as the second cut). In 1267, the medieval scientist Roger Bacon, writing in Latin, defined the division of time between full moons as a number of hours, minutes, seconds, thirds, and fourths ("horae", "minuta", "secunda", "tertia", and "quarta") after noon on specified calendar dates.
Thomas Fuller (mental calculator)
First, when they asked him how many seconds there were in a year and a half, he answered in about two minutes, 47,304,000. Second, when they asked how many seconds a man has lived who is 70 years, 17 days and 12 hours old, he answered in a minute and a half 2,210,500,800. One of the men was working out the problems on paper, and informed Fuller that he was wrong, because the answer was much smaller. Fuller hastily replied, "'Top, massa, you forget de leap year." When the leap year was added in, the sums matched.
Cosmic year (Chinese astrology)
Vedic scriptures delineate a cosmic cycle of creation and destruction marked by 4 Yugas. There is considerable debate on the duration of one Yuga, varying from 1200 to 432,000 or millions years. Swami Sri Yukteswar Giri estimates the duration of two total cycles (an descending and an ascending part) to comprise 24000 years. According to Vamadeva David Frawley the Yuga cycle relates to the precession of the equinoxes, thus suggesting a relationship with the platonic year. In the interpretations of these and other vedic scholars, modern times (1700–1900) have witnessed the end of the dark "Iron Age" (Kali Yuga), a notion supported by Rudolf Steiner.
Atomic clock
For context, a femtosecond () is to a second what a second is to about 31.71 million () years and an attosecond () is to a second what a second is to about 31.71 billion () years.
Julian year (astronomy)
In astronomy, a Julian year (symbol: a) is a unit of measurement of time defined as exactly 365.25 days of SI seconds each. The length of the Julian year is the average length of the year in the Julian calendar that was used in Western societies until some centuries ago, and from which the unit is named. Nevertheless, because astronomical Julian years are measuring duration rather than designating dates, this Julian year does not correspond to years in the Julian calendar or any other calendar. Nor does it correspond to the many other ways of defining a year.
Year
The sidereal year is the time taken for the Earth to complete one revolution of its orbit, as measured against a fixed frame of reference (such as the fixed stars, Latin "sidera", singular "sidus"). Its average duration is days (365 d 6 h 9 min 9.76 s) (at the epoch J2000.0 = January 1, 2000, 12:00:00 TT).
Solar term
Because the Sun's speed along the ecliptic varies depending on the Earth-Sun distance, the number of days that it takes the Sun to travel between each pair of solar terms varies slightly throughout the year. Each solar term is divided into three (候 "hòu") (), so there are 72 pentads in a year. Each pentad consists of five, rarely six, days, and are mostly named after phenological (biological or botanical) phenomena corresponding to the pentad.
Speed of light
In 1983 the 17th CGPM found that wavelengths from frequency measurements and a given value for the speed of light are more reproducible than the previous standard. They kept the 1967 definition of second, so the caesium hyperfine frequency would now determine both the second and the metre. To do this, they redefined the metre as: "The metre is the length of the path travelled by light in vacuum during a time interval of 1/ of a second." As a result of this definition, the value of the speed of light in vacuum is exactly and has become a defined constant in the SI system of units. Improved experimental techniques that prior to 1983 would have measured the speed of light, no longer affect the known value of the speed of light in SI units, but instead allow a more precise realization of the metre by more accurately measuring the wavelength of Krypton-86 and other light sources.
Al-Battani
One of al-Battānī's best-known achievements in astronomy was the determination of the solar year as being 365 days, 5 hours, 46 minutes and 24 seconds which is only 2 minutes and 22 seconds off.
Speed of light
Astronomical distances are sometimes expressed in light-years, especially in popular science publications and media. A light-year is the distance light travels in one year, around 9461 billion kilometres, 5879 billion miles, or 0.3066 parsecs. In round figures, a light year is nearly 10 trillion kilometres or nearly 6 trillion miles. Proxima Centauri, the closest star to Earth after the Sun, is around 4.2 light-years away.
Day
A day, symbol "d", defined as 86 400 seconds, is not an SI unit, but is accepted for use with SI. The Second is the base unit of time in SI units.
Middle-earth
The Appendices make several references in both history and etymology of topics 'now' (in modern English languages) and 'then' (ancient languages);
The year no doubt was of the same length,¹ ["the footnote here reads": 365 days, 5 hours, 48 minutes, 46 seconds.] for long ago as those times are now reckoned in years and lives of men, they were not very remote according to the memory of the Earth.
Universal Time
The rotation of the Earth is somewhat irregular, and is very gradually slowing due to tidal acceleration. Furthermore, the length of the second was determined from observations of the Moon between 1750 and 1890. All of these factors cause the mean solar day, on the average, to be slightly longer than the nominal 86,400 SI seconds, the traditional number of seconds per day. As UT is slightly irregular in its rate, astronomers introduced Ephemeris Time, which has since been replaced by Terrestrial Time (TT). Because Universal Time is synchronous with night and day, and more precise atomic-frequency standards drift away from this, however, UT is still used to produce a correction (called a leap second) to atomic time, in order to obtain a broadcast form of civil time that carries atomic frequency. Thus, civil broadcast standards for time and frequency usually follow International Atomic Time closely, but occasionally step (or "leap") in order to prevent them from drifting too far from mean solar time.
Hebrew calendar
A Metonic cycle equates to 235 lunar months in each 19-year cycle. This gives an average of 6939 days, 16 hours, and 595 parts for each cycle. But due to the Rosh Hashanah postponement rules (preceding section) a cycle of 19 Jewish years can be either 6939, 6940, 6941, or 6942 days in duration. Since none of these values is evenly divisible by seven, the Jewish calendar repeats exactly only following 36,288 Metonic cycles, or 689,472 Jewish years. There is a near-repetition every 247 years, except for an excess of about 50 minutes (905 parts).
IRIG timecode
In IRIG G, bits 50–53 encode hundredths of seconds, and the years are encoded in bits 60–68.
Light-second
Just as the second forms the basis for other units of time, the light-second can form the basis for other units of length, ranging from the light-nanosecond (299.8 mm or just under one international foot) to the light-minute, light-hour and light-day, which are sometimes used in popular science publications. The more commonly used light-year is also presently defined to be equal to precisely light-seconds, since the definition of a year is based on a Julian year (not Gregorian year) of exactly 365.25 days, each of exactly SI seconds.
Cosmological decade
When CÐ is measured in log( seconds/Ð ), "CÐ" 1 begins at 10 seconds and lasts 90 seconds (until 100 seconds after Time Zero). "CÐ" 100, the 100th cosmological decade, lasts from 10 to 10 seconds after Time Zero. CÐ formula_1 is Time Zero.
Year
The Great Year, or equinoctial cycle, corresponds to a complete revolution of the equinoxes around the ecliptic. Its length is about 25,700 years.
Julian day
As stated above, the Julian date (JD) of any instant is the Julian day number for the preceding noon in Universal Time plus the fraction of the day since that instant. Ordinarily calculating the fractional portion of the JD is straightforward; the number of seconds that have elapsed in the day divided by the number of seconds in a day, 86,400. But if the UTC timescale is being used, a day containing a positive leap second contains 86,401 seconds (or in the unlikely event of a negative leap second, 86,399 seconds). One authoritative source, the Standards of Fundamental Astronomy (SOFA), deals with this issue by treating days containing a leap second as having a different length (86,401 or 86,399 seconds, as required). SOFA refers to the result of such a calculation as "quasi-JD".
Tropical year
In the 2nd century BC Hipparchus measured the time required for the Sun to travel from an equinox to the same equinox again. He reckoned the length of the year to be 1/300 of a day less than 365.25 days (365 days, 5 hours, 55 minutes, 12 seconds, or 365.24667 days). Hipparchus used this method because he was better able to detect the time of the equinoxes, compared to that of the solstices .
Earth's rotation
Earth rotates once in about 24 hours with respect to the Sun, but once every 23 hours, 56 minutes, and 4 seconds with respect to the stars (see below). Earth's rotation is slowing slightly with time; thus, a day was shorter in the past. This is due to the tidal effects the Moon has on Earth's rotation. Atomic clocks show that a modern day is longer by about 1.7 milliseconds than a century ago, slowly increasing the rate at which UTC is adjusted by leap seconds. Analysis of historical astronomical records shows a slowing trend of about 2.3 milliseconds per century since the 8th century BCE.
Century
A century (from the Latin "centum", meaning "one hundred"; abbreviated c.) is a period of 100 years. Centuries are numbered ordinally in English and many other languages.
Second
In 1956, the second was redefined in terms of a year relative to that epoch. The second was thus defined as "the fraction of the tropical year for 1900 January 0 at 12 hours ephemeris time". This definition was adopted as part of the International System of Units in 1960.
Light-year
The light-year unit appeared a few years after the first successful measurement of the distance to a star other than the Sun, by Friedrich Bessel in 1838. The star was 61 Cygni, and he used a heliometer designed by Joseph von Fraunhofer. The largest unit for expressing distances across space at that time was the astronomical unit, equal to the radius of the Earth's orbit or In those terms, trigonometric calculations based on 61 Cygni's parallax of 0.314 arcseconds, showed the distance to the star to be astronomical units ( or ). Bessel added that light employs 10.3 years to traverse this distance. He recognized that his readers would enjoy the mental picture of the approximate transit time for light, but he refrained from using the light-year as a unit. He may have resented expressing distances in light-years because it would deteriorate the accuracy of his parallax data due to multiplying with the uncertain parameter of the speed of light. The speed of light was not yet precisely known in 1838; its value changed in 1849 (Fizeau) and 1862 (Foucault). It was not yet considered to be a fundamental constant of nature, and the propagation of light through the aether or space was still enigmatic. The light-year unit appeared, however, in 1851 in a German popular astronomical article by Otto Ule. The paradox of a distance unit name ending on "year"' was explained by Ule by comparing it to a hiking road hour ("Wegstunde"). A contemporary German popular astronomical book also noticed that light-year is an odd name. In 1868 an English journal labelled the light-year as a unit used by the Germans. Eddington called the light-year an inconvenient and irrelevant unit, which had sometimes crept from popular use into technical investigations.
Decimal time
In 1754, Jean le Rond d'Alembert wrote in the "Encyclopédie":
In 1788, Claude Boniface Collignon proposed dividing the day into 10 hours or 1000 minutes, each new hour into 100 minutes, each new minute into 1000 seconds, and each new second into 1000 "tierces" (Latin for "third"). The distance the twilight zone travels in one such "tierce" at the equator, which would be one-billionth of the circumference of the earth, would be a new unit of length, provisionally called a half-handbreadth, equal to four modern centimetres. Further, the new "tierce" would be divided into 1000 "quatierces", which he called "microscopic points of time". He also suggested a week of 10 days and dividing the year into 10 "solar months".
Watt
The watt second is a unit of energy, equal to the joule.
One kilowatt hour is 3,600,000 watt seconds.
Lincos (artificial language)
The next section of the Lincos dictionary introduces a word for second, "Sec," by playing pulses of various lengths, followed by Sec, and the number of seconds, "until the receiver may be expected to remark that the numbers... are proportional to the durations," thus teaching both that Sec is a unit of time, and exactly how long it is. He then introduces means for measuring durations, referring to moments in time, and talking about past and future events.
Unit of time
These units do not have a consistent relationship with each other and require intercalation. For example, the year cannot be divided into 12 28-day months since 12 times 28 is 336, well short of 365. The lunar month (as defined by the moon's rotation) is not 28 days but 28.3 days. The year, defined in the Gregorian calendar as 365.24 days has to be adjusted with leap days and leap seconds. Consequently, these units are now all defined as multiples of seconds.
Coordinated Universal Time
As the Earth's rotation continues to slow, positive leap seconds will be required more frequently. The long-term rate of change of LOD is approximately +1.7 ms per century. At the end of the 21st century, LOD will be roughly 86,400.004 s, requiring leap seconds every 250 days. Over several centuries, the frequency of leap seconds will become problematic.
Coordinated Universal Time
UTC divides time into days, hours, minutes and seconds. Days are conventionally identified using the Gregorian calendar, but Julian day numbers can also be used. Each day contains 24 hours and each hour contains 60 minutes. The number of seconds in a minute is usually 60, but with an occasional leap second, it may be 61 or 59 instead. Thus, in the UTC time scale, the second and all smaller time units (millisecond, microsecond, etc.) are of constant duration, but the minute and all larger time units (hour, day, week, etc.) are of variable duration. Decisions to introduce a leap second are announced at least six months in advance in "Bulletin C" produced by the International Earth Rotation and Reference Systems Service. The leap seconds cannot be predicted far in advance due to the unpredictable rate of rotation of the Earth.
Light-second
The light-second is a convenient unit for measuring distances in the inner Solar System, since it corresponds very closely to the radiometric data used to determine them. (The match is not exact for an Earth-based observer because of a very small correction for the effects of relativity.) The value of the astronomical unit (roughly the distance between Earth and the Sun) in light-seconds is a fundamental measurement for the calculation of modern ephemerides (tables of planetary positions). It is usually quoted as "light-time for unit distance" in tables of astronomical constants, and its currently accepted value is  s.Multiples of the light-second can be defined, although apart from the light-year, they are more used in popular science publications than in research works. For example, a light-minute is 60 light-seconds, and the average distance between Earth and the Sun is 8.317 light-minutes.
Sidereal time
Another way to see this difference is to notice that, relative to the stars, the Sun appears to move around Earth once per year. Therefore, there is one fewer solar day per year than there are sidereal days. This makes a sidereal day approximately times the length of the 24-hour solar day, giving approximately 23 h 56 min 4.1 s (86,164.1 s).
Adhik Maas
The Moon takes about 27.3 days to make one complete orbit around the earth. The earth orbits around the sun once every 365.2422 days (= earth’s orbital speed of 29.79 km per second). The earth and the moon in 27.3 days have moved as a system about 1/12 of the way around the sun. This means that from one full moon to the next full moon, the moon must travel 2.2 extra days before it appears again as a full moon, due to the curve of the earth’s orbit around the sun. Ultimately this creates a variance of 10.87 days a year between a lunar year and a solar year. To compensate for this difference, the additional month is added after every 32.5 months on average.
Words per minute
Morse code uses variable length sequences of short and long duration "signals" (dots and dashes) to represent source information e.g. sequences for the letter "K" and numeral "2" are respectively () and (). This variability complicates the measurement of Morse code speed rated in words per minute. Using telegram messages, the average English word length is about five characters, each averaging 5.124 dot durations or baud. Spacing between words should also be considered, being seven dot durations in the USA and five in British territories. So the average British telegraph word was 30.67 dot times. So the baud rate of a Morse code is × word per minute rate.
Foot per second squared
The foot per second squared (plural "feet per second squared") is a unit of acceleration. It expresses change in velocity expressed in units of feet per second (ft/s) divided by time in seconds (s) (or the distance in feet (ft) traveled or displaced, divided by the time in seconds (s) squared). The corresponding unit in the International System of Units (SI) is the metre per second squared.
Femtosecond
A femtosecond is the SI unit of time equal to 10 or / of a second; that is, one quadrillionth, or one millionth of one billionth, of a second. For context, a femtosecond is to a second as a second is to about 31.71 million years; a ray of light travels approximately 0.3 µm (micrometers) in 1 femtosecond, a distance comparable to the diameter of a virus.
Earth's rotation
The average of the true solar day during the course of an entire year is the "mean solar day", which contains solar seconds. Currently, each of these seconds is slightly longer than an SI second because Earth's mean solar day is now slightly longer than it was during the 19th century due to tidal friction. The average length of the mean solar day since the introduction of the leap second in 1972 has been about 0 to 2 ms longer than 86,400 SI seconds. Random fluctuations due to core-mantle coupling have an amplitude of about 5 ms. The mean solar second between 1750 and 1892 was chosen in 1895 by Simon Newcomb as the independent unit of time in his Tables of the Sun. These tables were used to calculate the world's ephemerides between 1900 and 1983, so this second became known as the ephemeris second. In 1967 the SI second was made equal to the ephemeris second.