A time standard is a specification for measuring time: either the rate at which time passes; or points in time; or both. In modern times, several time specifications have been officially recognized as standards, where formerly they were matters of custom and practice. An example of a kind of time standard can be a time scale, specifying a method for measuring divisions of time. A standard for civil time can specify both time intervals and time-of-day.

Standardized time measurements are made using a clock to count periods of some cyclic change, which may be either the changes of a natural phenomenon or of an artificial machine.

Historically, time standards were often based on the Earth's rotational period. From the late 17th century to the 19th century it was assumed that the Earth's daily rotational rate was constant.^[1] Astronomical observations of several kinds, including eclipse records, studied in the 19th century, raised suspicions that the rate at which Earth rotates is gradually slowing and also shows small-scale irregularities, and this was confirmed in the early twentieth century.^[2] Time standards based on Earth rotation were replaced (or initially supplemented) for astronomical use from 1952 onwards by an ephemeris time standard based on the Earth's orbital period and in practice on the motion of the Moon. The invention in 1955 of the caesium atomic clock has led to the replacement of older and purely astronomical time standards, for most practical purposes, by newer time standards based wholly or partly on atomic time.

Various types of second and day are used as the basic time interval for most time scales. Other intervals of time (minutes, hours, and years) are usually defined in terms of these two.

Time standards based on Earth rotation[link]

Apparent solar time ('apparent' is often used in English-language sources, but 'true' in French astronomical literature^[3]) is based on the solar day, which is the period between one solar noon (passage of the real Sun across the meridian) and the next. A solar day is approximately 24 hours of mean time. Because the Earth's orbit around the sun is elliptical, and because of the obliquity of the Earth's axis relative to the plane of the orbit (the ecliptic), the apparent solar day varies a few dozen seconds above or below the mean value of 24 hours. As the variation accumulates over a few weeks, there are differences as large as 16 minutes between apparent solar time and mean solar time (see Equation of time). However, these variations cancel out over a year. There are also other perturbations such as Earth's wobble, but these are less than a second per year.

Sidereal time is time by the stars. A sidereal rotation is the time it takes the Earth to make one revolution with respect to the stars, approximately 23 hours 56 minutes 4 seconds. For accurate astronomical work on land, it was usual to observe sidereal time rather than solar time to measure mean solar time, because the observations of 'fixed' stars could be measured and reduced more accurately than observations of the Sun (in spite of the need to make various small compensations, for refraction, aberration, precession, nutation and proper motion). It is well known that observations of the Sun pose substantial obstacles to the achievement of accuracy in measurement.^[4] In former times, before the distribution of accurate time signals, it was part of the routine work at any observatory to observe the sidereal times of meridian transit of selected 'clock stars' (of well-known position and movement), and to use these to correct observatory clocks running local mean sidereal time; but nowadays local sidereal time is usually generated by computer, based on time signals.^[5]

Mean solar time was originally apparent solar time corrected by the equation of time. Mean solar time was sometimes derived, especially at sea for navigational purposes, by observing apparent solar time and then adding to it a calculated correction, the equation of time, which compensated for two known irregularities, caused by the ellipticity of the Earth's orbit and the obliquity of the Earth's equator and polar axis to the ecliptic (which is the plane of the Earth's orbit around the sun).

Greenwich Mean Time (GMT) was originally mean time deduced from meridian observations made at the Royal Greenwich Observatory (RGO). The principal meridian of that observatory was chosen in 1884 by the International Meridian Conference to be the Prime Meridian. GMT either by that name or as 'mean time at Greenwich' used to be an international time standard, but is no longer so; it was initially renamed in 1928 as Universal Time (UT) (partly as a result of ambiguities arising from the changed practice of starting the astronomical day at midnight instead of at noon, adopted as from 1 January 1925). The more current refined version of UT, UT1, is still in reality mean time at Greenwich. Greenwich Mean Time is still the legal time in the UK (in winter, and as adjusted by one hour for summer time). But Coordinated Universal Time (UTC) (an atomic-based time scale which is always kept within 0.9 second of UT1) is in common actual use in the UK, and the name GMT is often inaccurately used to refer to it. (See articles Greenwich Mean Time, Universal Time, Coordinated Universal Time and the sources they cite.)

Universal Time (UT) is a time scale based on the mean solar day, defined to be as uniform as possible despite variations in Earth's rotation.

• UT0 is the rotational time of a particular place of observation. It is observed as the diurnal motion of stars or extraterrestrial radio sources.
• UT1 is computed by correcting UT0 for the effect of polar motion on the longitude of the observing site. It varies from uniformity because of the irregularities in Earth's rotation.

Time standards for planetary motion calculations[link]

Ephemeris time and its successor time scales described below have all been intended for astronomical use, e.g. in planetary motion calculations, with aims including uniformity, in particular, freedom from irregularities of Earth rotation. Some of these standards are examples of dynamical time scales and/or of coordinate time scales.

• Ephemeris Time (ET) was from 1952 to 1976 an official time scale standard of the International Astronomical Union; it was a dynamical time scale based on the orbital motion of the Earth around the Sun, from which the ephemeris second was derived as a defined fraction of the tropical year. This ephemeris second was the standard for the SI second from 1956 to 1967, and it was also the source for calibration of the caesium atomic clock; its length has been closely duplicated, to within 1 part in 10¹⁰, in the size of the current SI second referred to atomic time.^[6] This Ephemeris Time standard was non-relativistic and did not fulfil growing needs for relativistic coordinate time scales. It was in use for the official almanacs and planetary ephemerides from 1960 to 1983, and was replaced in official almanacs for 1984 and after, by numerically integrated Jet Propulsion Laboratory Development Ephemeris DE200 (based on the JPL relativistic coordinate time scale T_eph).

For applications at the Earth's surface, ET's official replacement was Terrestrial Dynamical Time (TDT), since redefined as Terrestrial Time (TT). For the calculation of ephemerides, TDB was officially recommended to replace ET, but deficiencies were found in the definition of TDB (though not affecting T_eph), and these led to the IAU defining and recommending further time scales, Barycentric Coordinate Time (TCB) for use in the solar system as a whole, and Geocentric Coordinate Time (TCG) for use in the vicinity of the Earth. As defined, TCB (as observed from the Earth's surface) is of divergent rate relative to all of ET, T_eph and TDT/TT;^[7] and the same is true, to a lesser extent, of TCG. The ephemerides of sun, moon and planets in current widespread and official use continue to be those calculated at the Jet Propulsion Laboratory (updated as from 2003 to DE405) using as argument T_eph.

• Terrestrial Dynamic Time (TDT) replaced Ephemeris Time and maintained continuity with it. TDT is a uniform atomic time scale, whose unit is the SI second. TDT is tied in its rate to the SI second, as is International Atomic Time (TAI), but because TAI was somewhat arbitrarily defined at its inception in 1958 to be initially equal to a refined version of UT, TT is offset from TAI, by a constant 32.184 seconds. The offset provided a continuity from Ephemeris Time to TDT. TDT has since been redefined as Terrestrial Time (TT).
• Barycentric Dynamical Time (TDB) is similar to TDT but includes relativistic corrections that move the origin to the barycenter. TDB differs from TT only in periodic terms. The difference is at most 2 milliseconds.

In 1991, in order to clarify the relationships between space-time coordinates, new time scales were introduced, each with a different frame of reference. Terrestrial Time is time at Earth's surface. Geocentric Coordinate Time is a coordinate time scale at Earth's center. Barycentric Coordinate Time is a coordinate time scale at the center of mass of the solar system, which is called the barycenter. Barycentric Dynamical Time is a dynamical time at the barycenter.^[8]

• Terrestrial Time (TT) is the time scale which had formerly been called Terrestrial Dynamical Time. It is now defined as a coordinate time scale at Earth's surface.
• Geocentric Coordinate Time (TCG) is a coordinate time having its spatial origin at the center of Earth's mass. TCG is linearly related to TT as: TCG - TT = L_G * (JD -2443144.5) * 86400 seconds, with the scale difference L_G defined as 6.969290134e-10 exactly.
• Barycentric Coordinate Time (TCB) is a coordinate time having its spatial origin at the solar system barycenter. TCB differs from TT in rate and other mostly periodic terms. Neglecting the periodic terms, in the sense of an average over a long period of time the two are related by: TCB - TT = L_B * (JD -2443144.5) * 86400 seconds. According to IAU the best estimate of the scale difference L_B is 1.55051976772e-08.

Constructed time standards[link]

International Atomic Time (TAI) is the primary international time standard from which other time standards, including UTC, are calculated. TAI is kept by the BIPM (International Bureau of Weights and Measures), and is based on the combined input of many atomic clocks around the world, each corrected for environmental and relativistic effects. It is the primary realisation of Terrestrial Time.

Coordinated Universal Time (UTC) is an atomic time scale designed to approximate Universal Time. UTC differs from TAI by an integral number of seconds. UTC is kept within 0.9 second of UT1 by the introduction of one-second steps to UTC, the "leap second". To date these steps have always been positive.

Standard time or civil time in a region deviates a fixed, round amount, usually a whole number of hours, from some form of Universal Time, now usually UTC. The offset is chosen such that a new day starts approximately while the sun is at the nadir. See Time zone. Alternatively the difference is not really fixed, but it changes twice a year a round amount, usually one hour, see Daylight saving time.

Other time scales[link]

Julian day number is a count of days elapsed since Greenwich mean noon on 1 January 4713 B.C., Julian proleptic calendar. The Julian Date is the Julian day number followed by the fraction of the day elapsed since the preceding noon. Conveniently for astronomers, this avoids the date skip during an observation night.

Modified Julian day (MJD) is defined as MJD = JD - 2400000.5. An MJD day thus begins at midnight, civil date. Julian dates can be expressed in UT, TAI, TDT, etc. and so for precise applications the timescale should be specified, e.g. MJD 49135.3824 TAI.

See also[link]

• Time signal
• Radio clock
• Orbital period as unit of time

Further reading[link]

1. ^ Before the time of John Flamsteed it was widely believed that the Earth's rotation had seasonal variations comparable in size with what is now called the equation of time. See articles on Vincent Wing and Thomas Streete for examples of astronomers before Flamsteed who believed this. The equation of time, correctly based on the two major components of the Sun's irregularity of apparent motion, i.e. the effect of the obliquity of the ecliptic and the effect of the Earth's orbital eccentricity, was not generally adopted until after John Flamsteed's tables of 1672/3, published with the posthumous edition of the works of Jeremiah Horrocks. See S Vince, "A Complete System of Astronomy", 2nd edition, volume 1, 1814, at p.49; see also Equation of time - history.
2. ^ See Ephemeris time - history, and sources shown there.
3. ^ See for example a recent description of "temps vrai" by the Bureau des Longitudes; and for an older example S Vince, 'A complete system of astronomy' (1814), esp. at page 46.
4. ^ See H A Harvey, "The Simpler Aspects of Celestial Mechanics", in Popular Astronomy 44 (1936), 533-541.
5. ^ A E Roy, D Clarke, 'Astronomy: Principles and Practice' (4th edition, 2003) at p.89.
6. ^ W Markowitz, R G Hall, L Essen, J V L Parry (1958), 'Frequency of caesium in terms of ephemeris time', Phys Rev Letters v1 (1958), 105-107; and Wm Markowitz (1988) 'Comparisons of ET(Solar), ET(Lunar), UT and TDT', in (eds.) A K Babcock & G A Wilkins, 'The Earth's Rotation and Reference Frames for Geodesy and Geophysics', IAU Symposia #128 (1988), at pp 413-418.
7. ^ P K Seidelmann & T Fukushima (1992), "Why new time scales?", Astronomy & Astrophysics vol.265 (1992), pages 833-838, including Fig. 1 at p.835, a graph giving an overview of the rate differences and offsets between various standard time scales, present and past, defined by the IAU.
8. ^ V Brumberg, S Kopeikin (1990), 'Relativistic time scales in the solar system', Celestial Mechanics and Dynamical Astronomy (1990), Vol. 48, 23-44

• Explanatory Supplement to the Astronomical Almanac, P. K. Seidelmann, ed., University Science Books, 1992, ISBN 0-935702-68-7

External links[link]

• Systems of Time by Dr. Demetrios Matsakis, Director, Time Service Dept., United States Naval Observatory
• USNO article on the definition of seconds and leap seconds
• A history of astronomical time scales by Steve Allen
• Astronomical times
• Why is a minute divided into 60 seconds, an hour into 60 minutes, yet there are only 24 hours in a day? Ask the Experts - March 5, 2007. SCIENTIFIC AMERICAN

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This biographical article needs additional citations for verification. Please help by adding reliable sources. Contentious material about living persons that is unsourced or poorly sourced must be removed immediately, especially if potentially libelous or harmful. (May 2008)

Kathy Mattea
Background information
Birth name	Kathleen Alice Mattea
Born	(1959-06-21) June 21, 1959 (age 53) South Charleston, West Virginia, United States
Origin	Cross Lanes, West Virginia, USA
Genres	Country
Occupations	Singer-songwriter
Instruments	Vocals Guitar
Years active	1975–present
Labels	Mercury Nashville MCA Narada
Associated acts	Tim O'Brien
Website	mattea.com

Kathleen Alice "Kathy" Mattea (pronounced ma-TAY-a)^[1] (born June 21, 1958, in South Charleston, West Virginia) is an American country music and bluegrass performer who often brings folk, Celtic and traditional country sounds to her music. Active since 1983 as a recording artist, she has recorded seventeen albums and has charted more than thirty singles on the Billboard Hot Country Singles & Tracks charts. This total includes the number one hits "Goin' Gone", "Eighteen Wheels and a Dozen Roses", "Come From the Heart" and "Burnin' Old Memories", as well as twelve additional Top Ten singles.

Life & career[link]

This section requires expansion with: Critical reception, info on each album, vocal and musical stylings.

Mattea was born in South Charleston, West Virginia, because it had the nearest hospital to her parents' home in Cross Lanes, where she grew up, graduating from nearby Nitro High School. She discovered her love of singing at Girl Scout camp. In 1976, while attending West Virginia University, she joined the bluegrass band Pennsboro, and two years later dropped out of school to move to Nashville. She worked as a tour guide at the Country Music Hall of Fame, did backup vocal work for Bobby Goldsboro, and sang demos for several Nashville songwriters and publishers including Nashville songwriter/producer Byron Hill who brought her to the attention of Frank Jones (then head of Mercury Records), who signed her to her first record deal in 1983.

Mattea's third album, 1986's folky Walk the Way the Wind Blows, proved to be her breakthrough both critically and commercially. Her cover of Nanci Griffith's "Love at the Five and Dime" was her first major hit, reaching #3 (and in addition, earned Griffith notice as a songwriter), and the album produced three other top ten songs: "Walk the Way the Wind Blows" (#10), "You're the Power"(#5), and "Train of Memories" (#6). "Love at the Five and Dime" also drew attention because well-known country singer Don Williams sang harmony vocals on the track.

Further hit songs include her first #1, "Goin' Gone"; the truck-driving song "Eighteen Wheels and a Dozen Roses" (1988); "Come From the Heart" and "Burnin' Old Memories" (both #1 hits in 1989); "She Came From Fort Worth" (1990); "Lonesome Standard Time" (1992); "Walking Away a Winner" (1994); "Nobody's Gonna Rain on Our Parade" (1994); "Maybe She's Human" (1994); and "455 Rocket" (1997, written by Gillian Welch^[2]). "Eighteen Wheels and a Dozen Roses" in late May 1988, became the first single by a solo female to spend multiple weeks at No. 1 on the Billboard country singles chart since Dolly Parton's "You're the Only One" in August 1979; both singles were on top of that chart for two weeks.

The heartrending "Where've You Been," which Mattea's husband Jon Vezner co-wrote with singer/songwriter Don Henry, reached #10 on the country chart and won her a 1990 Grammy for Best Female Country Vocal. Mattea is a repeat winner of the County Music Associations Female Vocalist of the Year, which she won on the success of "Eighteen Wheels and a Dozen Roses" and "Where've You Been."

Mattea won another Grammy in 1993 for her gospel-oriented Christmas album, Good News. Her first single from the album, "Mary, Did You Know?," went on to be covered by Kenny Rogers with Wynonna Judd, as well as Reba McEntire.

In 1994, Mattea collaborated with Suzy Bogguss, Alison Krauss, and Crosby, Stills, and Nash to contribute "Teach Your Children" to the AIDS benefit album Red Hot + Country produced by the Red Hot Organization. Also on that album, Mattea teamed up with Jackson Browne to contribute "Rock Me on the Water". Also through the '90s, she often collaborated with Scottish folksinger songwriter Dougie MacLean.

Mattea subsequently moved to MCA Nashville^[3] and, in 2000, released the ballad-heavy The Innocent Years, a heartfelt tribute to her ailing father. Wanting to explore her taste for Celtic folk, Mattea hopped labels to Narada, for whom she debuted in 2002 with the eclectic Roses.

With her social activism and her taste for songs with introspective lyrics, it has been often said that Mattea owes as much to the traditions of folk music as mainstream country.

Her 2008 release, Coal, combined her social activism with songs about coal-mining. It debuted at #64 on the country albums chart, and was nominated for a Grammy Award in the Traditional Folk category.

Kathy Mattea was honored as a member of the West Virginia Music Hall of Fame 2011 class of inductees. She enjoys strong support from a very active fan club, whose members refer to themselves as Matteaheads, and critical acclaim for her albums as she continues to tour and perform.

Social activism[link]

Mattea has been heavily involved in HIV/AIDS-related charities, beginning in the early 1990s, and is often credited with being among the first to champion this cause among the country music community. She is the recipient of the Minnie Pearl Humanitarian Award, and the Harvard AIDS Institute Leadership Award for this work.

She performed with Mary Chapin Carpenter on VH1's very first Save The Music concert, which also starred Bette Midler.

In 1991, Mattea took part in Voices That Care, a multi-artist project that featured other top names in music for a one-off single to raise money for the allied troops in the Gulf War. The project included Garth Brooks, Kenny Rogers, Randy Travis, and introduced Celine Dion to the American audience.

Mattea currently travels the country presenting Al Gore's An Inconvenient Truth and speaking to crowds about the importance of fighting global warming and the environmental and physical devastation of mountaintop removal coal mining.

Discography[link]

Further reading[link]

• Millard, Bob. (1998). "Kathy Mattea". In The Encyclopedia of Country Music. Paul Kingsbury, Editor. New York: Oxford University Press. pages 329–330.

References[link]

This biographical article needs additional citations for verification. Please help by adding reliable sources. Contentious material about living persons that is unsourced or poorly sourced must be removed immediately, especially if potentially libelous or harmful. (July 2008)

External links[link]

• Kathy Mattea's Official Website
• Kathy Mattea at the Internet Movie Database

Don Drummond (12 March 1932^[1][2][3] – 6 May 1969) was a Jamaican ska trombonist and composer. He was one of the original members of The Skatalites, and composed many of their tunes.

Drummond was born at the Jubilee Hospital in Kingston, Jamaica to Doris Monroe and Uriah Drummond.^[2] He was educated at Kingston's Alpha Boys School, where he later taught his younger schoolmate Rico Rodriguez to play the trombone.^[4]

His musical career began in 1950 with the Eric Dean's All-Stars.^[1] He continued into the 1960s with others, including Kenny Williams.

With the birth of ska Don joined The Skatalites. With Drummond's politicized conversion to the Rastafari movement, other band members followed his lead.^[5] He became a household name in Jamaica, before suffering mental problems. He was rated by pianist George Shearing to be amongst the world's top five trombone players.

In 1965 he was convicted of the murder of his longtime girlfriend, Anita "Marguerita" Mahfood, an exotic rhumba dancer and singer, on 1 January 1965. He was imprisoned at Belle Vue Asylum, Kingston where he remained until his death four years later. The official cause of death was "natural causes", possibly heart failure caused by malnutrition or improper medication,^[2] but other theories were put forward; some of his colleagues believed it was a government plot against the Kingston musical scene, and some believed that he was killed by gangsters as revenge for the murder of Mahfood.^[6]

References[link]

External links[link]

• Don Drummond at Allmusic
• Don Drummond discography at Discogs
• Short Don Drummond Biography
• Short biography at allaboutjazz.com
• Beyond The Mic: Don Drummond Remembered
• Splash and Ripple from Green Island: The Musical Legacy of Don Drummond