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Julian Year (astronomy)
In astronomy, a Julian year (symbol: a) is a unit of measurement of time defined as exactly 365.25 days of 7004864000000000000♠86400 SI seconds each.[1][2][3][4] The length of the Julian year is the average length of the year in the Julian calendar
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
Julian calendar
or any other calendar
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Simon Newcomb
Simon Newcomb
Simon Newcomb
(March 12, 1835 – July 11, 1909) was a Canadian–American astronomer, applied mathematician and autodidactic polymath, who was Professor of Mathematics
Mathematics
in the U.S
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International Astronomical Union
The International
International
Astronomical Union (IAU; French: Union astronomique internationale, UAI) is an international association of professional astronomers, at the PhD level and beyond, active in professional research and education in astronomy.[2] Among other activities, it acts as the internationally recognized authority for assigning designations to celestial bodies (stars, planets, asteroids, etc.) and any surface features on them.[3] The IAU is a member of the International
International
Council for Science (ICSU). Its main objective is to promote and safeguard the science of astronomy in all its aspects through international cooperation. The IAU maintains friendly relations with organizations that include amateur astronomers in their membership
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Earth
Earth
Earth
is the third planet from the Sun
Sun
and the only object in the Universe
Universe
known to harbor life. According to radiometric dating and other sources of evidence, Earth
Earth
formed over 4.5 billion years ago.[24][25][26] Earth's gravity interacts with other objects in space, especially the Sun
Sun
and the Moon, Earth's only natural satellite. Earth
Earth
revolves around the Sun
Sun
in 365.26 days, a period known as an Earth
Earth
year
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Gregorian Calendar
The Gregorian calendar
Gregorian calendar
is internationally the most widely used civil calendar.[1][2][Note 1] It is named after Pope Gregory XIII, who introduced it in October
October
1582. It was a refinement to the Julian calendar[3] involving an approximately 0.002% correction in the length of the calendar year. The motivation for the reform was to stop the drift of the calendar with respect to the equinoxes and solstices—particularly the northern vernal equinox, which helps set the date for Easter. Transition to the Gregorian calendar
Gregorian calendar
would restore the holiday to the time of the year in which it was celebrated when introduced by the early Church. The reform was adopted initially by the Catholic countries of Europe
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Calendar Date
A calendar date is a reference to a particular day represented within a calendar system. The calendar date allows the specific day to be identified. The number of days between two dates may be calculated. For example, "24 April 2018" is ten days after "14 April 2018" in the Gregorian calendar. The date of a particular event depends on the observed time zone. For example, the air attack on Pearl Harbor that began at 7:48 a.m. Hawaiian time on December 7, 1941, took place at 3:18 a.m. December 8 in Japan (Japan Standard Time). A particular day may be represented by a different date in another calendar as in the Gregorian calendar
Gregorian calendar
and the Julian calendar, which have been used simultaneously in different places. In most calendar systems, the date consists of three parts: the day of month, month, and the year. There may also be additional parts, such as the day of week
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Newcomb's Tables Of The Sun
Newcomb's Tables of the Sun is the short title and running head of a work by the American astronomer and mathematician Simon Newcomb entitled "Tables of the Motion of the Earth
Earth
on its Axis and Around the Sun" on pages 1–169 of "Tables of the Four Inner Planets" (1895),[1] volume VI of the serial publication Astronomical Papers Prepared for the Use of the American Ephemeris and Nautical Almanac. The work contains Newcomb's mathematical development of the position of the Earth
Earth
in the Solar System, which is constructed from classical celestial mechanics as well as centuries of astronomical measurements. The bulk of the work, however, is a collection of tabulated precomputed values that provide the position of the sun at any point in time. Newcomb's Tables were the basis for practically all ephemerides of the Sun published from 1900 through 1983, including the annual almanacs of the U.S
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Astronomy
Astronomy
Astronomy
(from Greek: ἀστρονομία) is a natural science that studies celestial objects and phenomena. It applies mathematics, physics, and chemistry, in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, moons, stars, galaxies, and comets; the phenomena include supernova explosions, gamma ray bursts, and cosmic microwave background radiation. More generally, all phenomena that originate outside Earth's atmosphere
Earth's atmosphere
are within the purview of astronomy. A related but distinct subject, physical cosmology, is concerned with the study of the Universe
Universe
as a whole.[1] Astronomy
Astronomy
is one of the oldest of the natural sciences
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Tropical Year
A tropical year (also known as a solar year) is the time that the Sun takes to return to the same position in the cycle of seasons, as seen from Earth; for example, the time from vernal equinox to vernal equinox, or from summer solstice to summer solstice. Because of the precession of the equinoxes, the seasonal cycle does not remain exactly synchronized with the position of the Earth
Earth
in its orbit around the Sun. As a consequence, the tropical year is about 20 minutes shorter than the time it takes Earth
Earth
to complete one full orbit around the Sun
Sun
as measured with respect to the fixed stars (the sidereal year). Since antiquity, astronomers have progressively refined the definition of the tropical year
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International System Of Units
The International System of Units
International System of Units
(SI, abbreviated from the French Système international (d'unités)) is the modern form of the metric system, and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units (ampere, kelvin, second, metre, kilogram, candela, mole) and a set of twenty decimal prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system also specifies names for 22 derived units for other common physical quantities like lumen, watt, etc. The base units, except for one, are derived from invariant constants of nature, such as the speed of light and the triple point of water, which can be observed and measured with great accuracy
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Greenwich Mean Time
Greenwich
Greenwich
Mean Time
Time
(GMT) is the mean solar time at the Royal Observatory in Greenwich, London. GMT was formerly used as the international civil time standard, now superseded in that function by Coordinated Universal Time
Coordinated Universal Time
(UTC). Today GMT is considered equivalent to UTC for UK civil purposes (but this is not formalised) and for navigation is considered equivalent to UT1 (the modern form of mean solar time at 0° longitude); these two meanings can differ by up to 0.9 s
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Adoption Of The Gregorian Calendar
The adoption of the Gregorian Calendar
Calendar
was an event in the modern history of most nations and societies, marking a change from their traditional (or old style) dating system to the modern (or new style) dating system that is widely used around the world today. Some countries adopted the new calendar from 1582, some did not do so before the early twentieth century, and others did so at various dates between; however a number continue to use a different civil calendar. For many the new style calendar is only used for civil purposes and the old style calendar remains used in religious contexts
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Special
Special
Special
or the specials or variation, may refer to:.mw-parser-output .tocright float:right;clear:right;width:auto;background:none;padding:.5em 0 .8em 1.4em;margin-bottom:.5em .mw-parser-output .tocright-clear-left clear:left .mw-parser-output .tocright-clear-both clear:both .mw-parser-output .tocright-clear-none clear:none Contents1 Policing 2 Literature 3 Film and television 4 Music4.1 Albums 4.2 Songs5 Computing 6 Other uses 7 See alsoPolicing[edit] Specials, Ulster
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SI
The International System of Units
International System of Units
(SI, abbreviated from the French Système international (d'unités)) is the modern form of the metric system, and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units (ampere, kelvin, second, metre, kilogram, candela, mole) and a set of twenty decimal prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system also specifies names for 22 derived units for other common physical quantities like lumen, watt, etc. The base units, except for one, are derived from invariant constants of nature, such as the speed of light and the triple point of water, which can be observed and measured with great accuracy
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Day
A day, a unit of time, is approximately the period of time during which the Earth completes one rotation with respect to the Sun
Sun
(solar day).[1][2] 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.[3] A civil day is usually 86 400 seconds, plus or minus a possible leap second in Coordinated Universal Time
Time
(UTC), and occasionally plus or minus an hour in those locations that change from or to daylight saving time. In common usage, it is either an interval equal to 24 hours[4] or daytime, the consecutive period of time during which the Sun
Sun
is above the horizon
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Time
Time
Time
is the indefinite continued progress of existence and events that occur in apparently irreversible succession from the past through the present to the future.[1][2][3] Time
Time
is a component quantity of various measurements used to sequence e
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