Epoch (reference date)

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Topic: Epoch (reference date)

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	J2000.0 - Enpsychlopedia
		Since the right ascension and declination of stars are constantly changing due to precession, (and, for relatively nearby stars due to proper motion), astronomers always specify these with reference to a particular epoch.
		Novices are sometimes confused by finding that the Earth's rotational North pole does not point quite at the J2000 celestial pole at the epoch J2000.0; the reason is that the true pole of epoch suffers nutation ("is nutated") away from the mean one.
		The earlier epoch that was in standard use was the B1950.0 epoch.
	www.grohol.com /psypsych/wiki/J2000

	AllRefer.com - Pleistocene epoch (Geology And Oceanography) - Encyclopedia
		More articles from AllRefer Reference on Pleistocene epoch
		You are here : AllRefer.com > Reference > Encyclopedia > Geology And Oceanography > Pleistocene epoch
		Since the interglacial periods of the Pleistocene were of longer duration than the time elapsed since the end of the Pleistocene 11,000 years ago, it is sometimes suggested that the Holocene, or Recent, epoch, which is occurring now, may be merely another such interglacial stage and that the glaciers may return at some future time.
	reference.allrefer.com /encyclopedia/P/Pleistoc.html (248 words)

	Ordnance Survey Ireland :: Geodetic services :: Overview :: GPS Reference Systems
		Thus different co-ordinate systems are established, within the defining reference frame, linked to the epoch of the observation, and transformations have been defined between them, which move positions from those determined at the time of observations to a common system at a defined epoch.
		WGS84 is a geocentric reference ellipsoid and a geodetic datum, in that it defines the centre of mass of the earth as its origin, and the direction of the earth's axis as the minor axis of the reference ellipsoid.
		The adoption of regional or local reference ellipsoids results in different positions for the same point along common boundaries between two different regions.
	www.osi.ie /gps/overview/gps.asp (918 words)

	epoch - OneLook Dictionary Search
		Words similar to epoch: era, age, date of reference, period, more...
		noun: (astronomy) the precise date that is the point of reference for which information (as coordinates of a celestial body) is referred
		Phrases that include epoch: epoch making, pleistocene epoch, holocene epoch, miocene epoch, oligocene epoch, more...
	www.onelook.com /cgi-bin/cgiwrap/bware/dofind.cgi?word=epoch (304 words)

	epoch (HyperDic hyper-dictionary)
		(astronomy) the precise date that is the point of reference for which information (as coordinates of a celestial body) is referred.
		(astronomy) the precise date that is the point of reference for which information (as coordinates of a celestial body) is referred
		Holocene, Holocene epoch, Recent, Recent epoch; Pleistocene, Pleistocene epoch, Glacial epoch; Pliocene, Pliocene epoch; Miocene, Miocene epoch; Oligocene, Oligocene epoch; Eocene, Eocene epoch; Paleocene, Paleocene epoch
	www.hyperdic.net /dic/epoch.htm (162 words)

	refsys_gb
		The reference frame of coordinates determined from point positioning will be identical to the reference frame of the satellite orbits, which is used to determine the satellite positions at signal emission time.
		In addition, each of these systems, consisting of a set of theoretical definitions, can only be used in practice if it has an associated reference frame.
		If the coordinates of the reference stations refer to a different reference frame than the satellite orbits, then the relation between both references needs to be known.
	www.gps.oma.be /gb/refsys_gb.htm (162 words)

	refsys_gb
		The reference frame of coordinates determined from point positioning will be identical to the reference frame of the satellite orbits, which is used to determine the satellite positions at signal emission time.
		In addition, each of these systems, consisting of a set of theoretical definitions, can only be used in practice if it has an associated reference frame.
		If the coordinates of the reference stations refer to a different reference frame than the satellite orbits, then the relation between both references needs to be known.
	www.gps.oma.be /gb/refsys_gb.htm (162 words)

	Epoch - Wikipedia, the free encyclopedia
		an epoch date, an instant of origin chosen as the reference from which time is measured in a calendar era or in a computer system.
		an epoch (astronomy), a moment in time for which celestial coordinates or orbital elements are specified.
		Epoch (comics), a supervillian written in DC comics also known as the Lord of Time
	www.wikipedia.org /wiki/Epoch (184 words)

	Epoch - Wikipedia, the free encyclopedia
		In computing and telecommunications, an epoch date is a specific date and time used as the reference for all other times.
		The epoch of a calendar era is the year, day, or instant from which the later (and earlier) years of a calendar are counted.
		In astronomy, an epoch (astronomy) is a moment in time for which celestial coordinates or orbital elements are specified.
	en.wikipedia.org /wiki/Epoch (333 words)

	Epoch date - Wikipedia, the free encyclopedia
		In telecommunications, an epoch date is a date in history chosen as the reference date from which time is measured.
		Another famous epoch date is January 1, 1970, the date from which Unix time is measured.
		One example of an epoch date is the beginning instant of January 1, 1900, Universal Time, for Transmission Control Protocol/Internet Protocol (TCP/IP).
	www.wikipedia.org /wiki/Epoch_date (123 words)

	year
		The sidereal year is the time for the Earth to complete one revolution of its orbit, as measured in a fixed frame of reference (such as the fixed stars, Latin sidus).
		An approximate formula to compute the current time in Besselian years from the Julian day is:
		The Besselian year is a tropical year that starts when the mean Sun reaches the ecliptic longitude of 280°.
	www.yourencyclopedia.net /Year.html (1019 words)

	Epoch date -- Facts, Info, and Encyclopedia article
		In ((often plural) systems used in transmitting messages over a distance electronically) telecommunication, an epoch date is a (A meeting arranged in advance) date in history, chosen as the reference date from which (The continuum of experience in which events pass from the future through the present to the past) time is measured.
		Note 2: TCP/IP programs exchange date or time-of-day (A message received and understood) information with time expressed as the number of seconds past the epoch date.
		See also (A unit of geological time) epoch, (A major division of geological time; an era is usually divided into two or more periods) era
	www.absoluteastronomy.com /encyclopedia/e/ep/epoch_date.htm (128 words)

	10.4 PRECESS - Astronomical Coordinate Conversion
		The FK4 system is tied to the equatorial coordinate system for Besselian epoch B1950.0, while the more accurate FK5 system is tied to the equatorial system for Julian epoch J2000.0.
		This definition depends on epoch because of precession; its practical implementation also depends on the set of fundamental reference stars used to measure coordinates.
		Ecliptic coordinates are weakly epoch dependent, so the user may wish to use a specific epoch to define the orbital plane rather than the default B1950.0.
	ledas-cxc.star.le.ac.uk /udocs/docs/PG/html/node76.html (1449 words)

	Glossary of astronomical terms
		An excellent reference on this topic is Astronomical Photometry: A Guide, by C. Sterken and J. Manfroid (1992, Dordrecht: Kluwer Academic Publishers).
		Due to precession, this point moves over time, so positions of stars in catalogues and on atlases are usually referred to a "mean equator and equinox" of a specified standard epoch.
		In astronomy, the measurement of the light emitting from astronomical objects, generally in the visible or infrared bands, in which a specific or general wavelength band is normally specified.
	cfa-www.harvard.edu /icq/ICQGlossary.html (3501 words)

	ZDP: Object Reference
		A DateTime object's value must generally be between Jan 1, 1970 (or your local machine epoch) and Jan 2038 to produce a valid time.time() style value.
		Return the permission mapping for the object This is a list of dictionaries with: permission_name, The name of the native object permission class_permission, The class permission the permission is mapped to.
		The first item is the object's id, the second is it path relative to the 'obj' argument.
	zdp.zope.org /projects/zqr/ZQR/objectreference (3501 words)

	Brewer, E. Cobham. Dictionary of Phrase & Fable. Julian Period
		B.C. dates to the Julian, we must subtract them from 4713, but our
		A.D. dates we must add to that number.
		Shaw, G.B. Stein, G. Stevenson, R.L. Wells, H.G. Reference > Brewer’s Dictionary > Julian Period
	www.bartleby.com /81/9352.html (3501 words)

	Reworking the clock command
		The Julian epoch is chosen because many existing calendar algorithms, such as those published in the second edition of Reingold [ 2 ], use Julian day number as their internal representation.
		You are probably doing that already, but manipulating dates internally via julian dates (just doubles in fact expressing date/time as the number of days and fractions thereof) makes life quite a bit easier.
		Most systems return absolute time as a count of nominal seconds of UTC from some epoch, ignoring leap seconds; two times that are a day apart will show precisely 86400 seconds (never 86399 nor 86401) between them, even if a leap second has occurred in between.
	wiki.tcl.tk /2495 (3501 words)

	Glossary of astronomical terms
		See separate definitions for Besselian year and Julian year.) The differences in an object's position when given in equinoxes 1950.0 and 2000.0 amounts to several arc minutes.
		For the purposes of the positions of objects dealt with in these ICQ/CBAT/MPC Web pages, the positions are almost always given for "equinox J2000.0", meaning that the reference system is that at the beginning of the year 2000; prior to 1992, most astronomers were using "equinox B1950.0".
		Due to precession, this point moves over time, so positions of stars in catalogues and on atlases are usually referred to a "mean equator and equinox" of a specified standard epoch.
	cfa-www.harvard.edu /iau/icq/ICQGlossary.html (3501 words)

	Second
		Reference to the year 1900 does not mean that this is the epoch of a mean solar day of 86,400 seconds.
		Rather, it is the epoch of the tropical year of 31,556,925.9747 seconds of ephemeris time.
		The Earth's motion was described in Newcomb's Tables of the Sun/, which provides a formula for the motion of the Sun at the epoch 1900 based on astronomical observations made during the eighteenth and nineteenth centuries.
	www.infothis.com /find/Second (772 words)

	TIME-BINDING: Second Paper
		Perhaps the clarifications on the private level do not clear up the public, or scientific, level which represents the creeds of a certain epoch, and so might be in agreement with the general development of the race.
		It is interesting to note that "epoch-making discoveries" are seldom if ever isolated; usually they come in bundles, being discovered by several individuals independently; they are "in the air," as we say—perhaps they are in the protoplasm more than in the air.
		We should not be surprised that, under such circumstances, the "motional" and "emotional" systems of science and philosophy, systems which make rigorous rationality impossible, are the remains of the pre-human, pre-cortex epoch of development.
	www.esgs.org /uk/art/ak8.htm (16725 words)

	JewelDate-0.1.php Function Reference
		Determine seconds since the UNIX epoch (00:00:00 01 Jan 1970 UTC) from the Gregorian Date.
		Determine Gregorian Date from the number of seconds since the UNIX epoch (00:00:00 01 Jan 1970 UTC).
		Return the Julian Date Number for the Ordinal day of year.
	jeweltools.sourceforge.net (16725 words)

	Coordinate Keywords
		Because the FK4 reference frame is not inertial--there is a small but significant rotation relative to distant objects--the epoch or time of observation is required to specify when the mean place was correct.
		keyword) is interpreted as a Besselian epoch and under FK5 as a Julian epoch.
		Use of this keyword permits greater precision than
	stdatu.stsci.edu /fits/users_guide/node60.html (199 words)

	EUREF Permanent GPS Network - Data & Products - Products
		The switch from one realization to its successor (for example from ITRF94 to ITRF96) is done simultaneously with the update of the reference frame used for the compution of the IGS orbits.
		The weekly combined EUREF solution, available in the ITRFxx, at the epoch of observation can be linked to the European Terrestrial Reference System ( ETRS89) by applying the " Guidelines for Reference Frame Fixing ".
		This guarantees the consistency between the reference frame used for the orbits (which are kept fixed for all EUREF computations) and the constraints on the coordinates.
	www.epncb.oma.be /_dataproducts/products (199 words)

	skycalc.c
		J2000, which\n"); printf("involves a small change of inertial reference frame!)\n\n"); } printf("Give epoch to precess from:"); scanf("%lf",&orig_epoch); printf("Give epoch to precess to:"); scanf("%lf",&final_epoch); dt = final_epoch - orig_epoch; while(rorig >= 0.) { printf("\nGive RA for %7.2f (h m s, -1 0 0 to exit):",orig_epoch); rorig = get_coord(); if(rorig
		An option to set the date and time to correspond to a given julian date was also added.
		The day and date are now based on the same rounding of the julian date, so they should always agree.
	zimmer.csufresno.edu /~fringwal/skycalc.c (199 words)

	Charles_lyell
		Principles of Geology: Being an Attempt to Explain the Former Changes of the Earth's Surface by Reference to Causes Now in Operation: 1830-1833
		The geological evidences of the antiquity of man,: With an outline of glacial and post-tertiary geology and remarks on the origin of species, with special...
		The Geological Evidences of the Antiquity of Man With an Outline of Glacial and Post-Tertiary Geology and Remarks on the Origin of Species
	books.mysic.com /Author/Charles_Lyell (199 words)

	McGraw-Hill AccessScience: Glacial epoch
		The most recent glacial epoch, better known as the Pleistocene glacial epoch, and also by the older term Quaternary period, encompassed at least the last 3
		n informal reference to a time during the history of the Earth when there were larger ice sheets (continental size) and mountain glaciers than there are today.
		Look here for more information about this article.
	dx.doi.org /10.1036/1097-8542.290100 (199 words)

	Globe of Blogs ::: Browse by Weblog Topic ::: Education and Reference ::: Mathematics
		Besselian Epoch Of My Digital Mind's Eye, The ::: Gerald
		Blog of a Rhode Island based math prof and long time Unix aficionado.
	www.globeofblogs.com /?x=topic&topic=82 (396 words)

	Merriam-Webster Online
		3 : an instant of time or a date selected as a point of reference (as in astronomy)
		Etymology: Medieval Latin epocha, from Greek epochE cessation, fixed point, from epechein to pause, hold back, from epi- + echein to hold -- more at
		For More Information on "epoch" go to Britannica.com
	www.m-w.com /cgi-bin/dictionary?book=Dictionary&va=epoch (158 words)

	EUREF Permanent GPS Network - Data & Products - Products
		The switch from one realization to its successor (for example from ITRF94 to ITRF96) is done simultaneously with the update of the reference frame used for the compution of the IGS orbits.
		The weekly combined EUREF solution, available in the ITRFxx, at the epoch of observation can be linked to the European Terrestrial Reference System ( ETRS89) by applying the " Guidelines for Reference Frame Fixing ".
		This guarantees the consistency between the reference frame used for the orbits (which are kept fixed for all EUREF computations) and the constraints on the coordinates.
	www.epncb.oma.be /_dataproducts/products (158 words)

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Topic: Epoch (reference date)

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