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Topic: Julian epoch

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Besselian epoch

Julian date

Year

Gregorian Calendar

J2000

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	Epoch (astronomy) - Wikipedia, the free encyclopedia
		The prefix "J" indicates that it is a Julian epoch.
		The "B" in the prefix indicates that it is a Besselian epoch, as opposed to a Julian epoch.
		The "J" in the prefix indicates that it is a Julian epoch, as opposed to a Besselian epoch.
	en.wikipedia.org /wiki/Epoch_(astronomy) (934 words)

	Julian year (astronomy) - Wikipedia, the free encyclopedia
		Julian years are used primarily for convenience in ephemeris work where stating a number of days would be unwieldy (for instance, it is easier to express the orbital period of Pluto as 248 Julian years rather than 90,590 days).
		A Julian day (or Julian date) is not a unit of time, but simply a running count of days with an arbitrarily chosen starting point in the distant past, with each day numbering one greater than the previous; it's a way to specify a date without reference to months or years.
		The Julian epoch J2000.0 is synchronized to exactly 12:00 TT (close to but not exactly Greenwich mean noon) on January 1, 2000 in the Gregorian (not Julian!) calendar, and future epochs can be calculated and named according to the number of days since then, divided by 365.25.
	en.wikipedia.org /wiki/Julian_year_(astronomy) (690 words)

	julian - definition by dict.die.net
		Julian calendar, the calendar as adjusted by Julius C[ae]sar, in which the year was made to consist of 365 days, each fourth year having 366 days.
		Julian epoch, the epoch of the commencement of the Julian calendar, or 46 b.
		Julian year, the year of 365 days, 6 hours, adopted in the Julian calendar, and in use until superseded by the Gregorian year, as established in the reformed or Gregorian calendar.
	dict.die.net /julian (121 words)

	ccget
		Julian equinoxes are prefixed by a J or j, Besselian equinoxes by a B or b.
		Epoch is the epoch of the observation and may be a Julian epoch, a Besselian epoch, or a Julian date.
		Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
	stsdas.stsci.edu /cgi-bin/gethelp.cgi?ccget (2264 words)

	Emperor Julian & Neo-Platonism
		Authorities agree that Julian was much loved as a just and humane ruler, adored by his troops for his fairness and consideration for their welfare, never asking them to do anything that he would not do himself.
		Julian's brief but active reign was at an end; yet the impetus he had given his reforms carried their influence in some degree into the after years.
		Julian emphasizes continually that Helios brings about the various activities of his solar realm, not directly to the beings, but through the means of countless other gods (angels, daemons, heroes, and others in the nature of archetypes who do not come into incarnation) -- what we might call the forces of nature.
	library.flawlesslogic.com /julian_2.htm (3995 words)

	[No title]
		Julian Julian calendar Gregorian The two calendars most frequently used by astronomers are the Julian and Gregorian calendars.
		The "J" indicates a Julian epoch, as distinguished from the older "B" or Besselian epoch.
		Julian epochs measure the year as 365.25 days exactly, the length of a year in the old Julian calendar; Besselian epochs have 365.2421988 days, matching a "real" (tropical) year.
	www.projectpluto.com /gloss/help_11.htm (2902 words)

	Epoch (Site not responding. Last check: 2007-10-31)
		Both sorts of epoch superficially resemble years AD but are not tied to the civil (Gregorian) calendar; to distinguish them from ordinary calendar-years there is often a ``.0'' suffix (as in ``1950.0''), although any other fractional part is perfectly legal (e.g.
		The new system, Julian epoch, was adopted as part of the IAU 1976 revisions (about which more will be said in due course) and came formally into use at the beginning of 1984.
		It uses the Julian year of exactly 365.25 days; Julian epoch 2000 is defined to be 2000 January 1.5 in the TT timescale.
	star-www.rl.ac.uk /star/docs/sun67.htx/node209.html (349 words)

	Julian epoch
		It is often convenient to used the standard epoch, J2000.0, for example, in star catalogs.
		The prefix "J" is added to distinguish this epoch from the more complicated Besselian epoch (see Besselian year) used before 1984.
		The standard epoch is defined as J2000.0 = 2000 January 1.5 = 2000 January 1 12h TDB.
	www.daviddarling.info /encyclopedia/J/Julian_epoch.html (168 words)

	TDDB28 Kursmaterial
		Thus the Besselian epoch is always somewhat out of sync with the wall calendar (B1950.0 occured at 1950 Jan 0.923).
		Either epoch measure is only a convenient approximation to our civil calendar and the Julian epoch corresponds as accurately to the wall calendar as the Besselian for the first hundred years or so ("standard epochs" are typically updated every 50 years).
		While all equinox epochs are equally valid for measurement, using standard epochs facilitates intercomparison of datasets.
	www.ida.liu.se /~TDDB28/mtrl/lab/astro_coord.sv.shtml (1747 words)

	Julian Date Converter (Site not responding. Last check: 2007-10-31)
		Julian dates (abbreviated JD) are simply a continuous count of days and fractions since noon Universal Time on January 1, 4713 BCE (on the Julian calendar).
		This application assumes that the changeover from the Julian calendar to the Gregorian calendar occurred in October of 1582, according to the scheme instituted by Pope Gregory XIII.
		Thus, there is a ten-day gap in calendar dates, but no discontinuity in Julian dates or days of the week: 4 October 1582 (Julian) is a Thursday, which begins at JD 2299159.5; and 15 October 1582 (Gregorian) is a Friday, which begins at JD 2299160.5.
	aa.usno.navy.mil /data/docs/JulianDate.html (570 words)

	CSPICE Routines: UTC2ET_C
		Although this routine is intended primarily for the conversion of epochs during the "space age" it may also be used to convert much earlier epochs.
		However, before using this routine to convert epochs prior to 1972 you must be sure that the assumptions made by in the implementation are consistent with the accuracy of the input calendar string.
		Prior to that epoch the Julian calendar was used for the recording of epochs.
	www.gps.caltech.edu /~marsdata/cspice/utc2et_c.html (738 words)

	Coordinate Converter Help
		The epoch of the equinox to be used as the special coordinate system.
		The epoch may be preceded by a B or J to indicate a Besselian or Julian input epoch.
		The epoch of observation is assumed to be 1950.
	heasarc.gsfc.nasa.gov /Tools/convcoord_help.html (1126 words)

	Glossary of astronomical terms
		The recent change to Julian year usage in dynamical astronomy (and the J2000.0 equinox) took effect in solar-system ephemerides of the Minor Planet Center and Central Bureau for Astronomical Telegrams on Jan. 1, 1992.
		Either of the two points (vernal, autumnal) on the celestial sphere where the ecliptic (which is the apparent path of the sun on the sky) intersects the celestial equator.
		When this dynamical, artificial "Julian year" is employed, a letter "J" prefixes the year.
	cfa-www.harvard.edu /icq/ICQGlossary.html (3501 words)

	Epochs and Eras
		The Islamic era begins with 16 July 622, Julian, although sometimes 15 July 622 is regarded as the beginning of that era.
		As in the Islamic calendar, in the Persian calendar the years are counted beginning with the Julian year 622.
		But the exact epoch is not 15 or 16 July, but 22 March 622, Julian, the day of the vernal equinox that year.
	www.ortelius.de /kalender/era_en.php (1664 words)

	ephemeris.com Space and Time, Solar System (Site not responding. Last check: 2007-10-31)
		Besselian epochs are written staring with a 'B', for example, B1950.0.
		As an example, take the Julian Epoch J2000.0, which is JD 2451545.0.
		This tilt is called the Obliquity of the Ecliptic, and is defined for the epoch J2000.0 as being 23.4392911 degrees (approximately 23.5 degrees).
	ephemeris.com /space-time.html (1774 words)

	1913Dictionary.com > Julian (Site not responding. Last check: 2007-10-31)
		julian calendar, the calendar as adjusted by julius candaelig;sar, in which the year was made to consist of 365 days, each fourth year having 366 days.
		-- julian epoch, the epoch of the commencement of the julian calendar, or 46 b.
		-- julian year, the year of 365 days, 6 hours, adopted in the julian calendar, and in use until superseded by the gregorian year, as established in the reformed or gregorian calendar.
	www.1913dictionary.com /dictionary/word/julian (307 words)

	Section 5.4 Ephemeris Services
		MEME of Epoch: mean equator mean equinox referenced to the specified Julian epoch.
		TEME of Epoch: true equator mean equinox referenced to the specified Julian epoch.
		Displays the Start epoch, the Duration, and the Stop epoch of the ephemeris, and is linked to the epoch of the Spacecraft State display.
	www.integ.com /OasysManual/sect_5/sect5_4.htm (3011 words)

	[No title]
		Because such a star has, in general, a non-zero proper motion in the FK4 system, the routine requires the epoch at which the position in the FK4 system was determined.
		At epoch 2000, and measuring on the sky rather than in terms of dRA, the errors resulting from this simplification are less than 1 milliarcsecond in position and 1 milliarcsecond per century in proper motion.
		Conversions involving other epochs will require use of the appropriate precession routines before and after this routine is called.
	cfa-www.harvard.edu /~john/starbase/slalink.p.html (765 words)

	The Time
		Incidentally, the so-called “light year” (a unit of distance, not time) is the length of the path traveled by light in vacuum in one Julian year, which is therefore (taking into account the definition of the SI meter) exactly 9460730472580800 meters.
		Between 1955 and 1958, a joint experiment of the National Physical Laboratory (UK, where the first cesium frequency samples had be obtained) and the US Naval Observatory was conducted to measure the value of the cesium 133 atom's hyperfine transition frequency (in the then-standard ephemeris second).
		Before the Julian reform, it is about impossible to date anything; “July” was called Quinctilis before it was dedicated to C. Julius Cæsar, but the number of days in a month was very variable, and some years even had 13 months with Mercedonius being the 13th.
	www.madore.org /~david/misc/time.html (3957 words)

	Why March 21st?
		It is said that March 21st was selected as the ecclesiastical vernal equinox because the Church of Alexandria, whose staff were reputed to have astronomical expertise, reckoned that March 21st was the date of the equinox in 325 AD, the year of the First Council of Nicaea.
		The Gregorian and Revised Julian calendars will have identical dates until March 1st, 2800 (because 2800 will be a Gregorian leap year but will not be a Revised Julian leap year).
		In non-leap years on the Julian, Gregorian, and Revised Julian calendars, March 21st is day number 80, counting January 1 as day number 1, so 79 days elapse prior to March 21st.
	individual.utoronto.ca /kalendis/mar21.htm (1848 words)

	Julian Day Calculations (Gregorian Calendar)
		The Julian Day Count is a uniform count of days from a remote epoch in the past (-4712 January 1, 12 hours Greenwich Mean Time (Julian proleptic Calendar) = 4713 BCE January 1, 12 hours GMT (Julian proleptic Calendar) = 4714 BCE November 24, 12 hours GMT (Gregorian proleptic Calendar)).
		This is the Julian Day Number for the beginning of the date in question at 0 hours, Greenwich time.
		To convert a Julian Day Number to a Gregorian date, assume that it is for 0 hours, Greenwich time (so that it ends in 0.5).
	quasar.as.utexas.edu /BillInfo/JulianDatesG.html (672 words)

	The Year 2000 Transition
		One way is to make the assumption, for example, that any Keplerian Epoch year value 78 through 99 has a century value of 19, and any year value 00 through 77 has a century value of 20.
		In other orbital calculations, the Julian date difference between the Keplerian Epoch year value and the Julian day value for January 1, 2000 is used.
		Still, it is necessary to convert the two digit Epoch year value to a four digit year value to obtain the Epoch Julian date.
	www.amsat.org /amsat/features/y2k_transition.html (2644 words)

	General Functions (Site not responding. Last check: 2007-10-31)
		For approximate purposes, the result of this routine consists of an integral part which gives the year AD and a fractional part which represents the distance through that year, so that for instance 2000.5 is approximately 1 July 2000.
		For approximate purposes, the argument of this routine consists of an integral part which gives the year AD and a fractional part which represents the distance through that year, so that for instance 2000.5 is approximately 1 July 2000.
		For approximate purposes, the argument of this routine consists of an integral part which gives the year AD and a fractional part which represents the distance through that year, so that for instance 1950.5 is approximately 1 July 1950.
	www.star.bris.ac.uk /~mbt/topcat/sun253/generalJel.html (2206 words)

	Day Numbers
		The Julian epoch is not old enough for the purposes of computing Biblical dates while keeping the Julian day number positive.
		By assigning an Epoch here, all days since the first day of the first year of Adam are numbered with a positive number.
		The negative Julian Day number for the AA Number epoch can be seen in the previous report.
	www.bibletime.com /tool/spec/daybynumber/index.html (552 words)

	Appendix A The Input File
		The epoch is optional only if the information is supplied later in a time record (see next item).
		A Besselian epoch implies the pre IAU 1976 system (as used in the FK4 catalog) and a Julian epoch implies the post IAU 1976 system (as used in the FK5 catalog).
		In the absence of a prefix, epochs before 1984.0 are assumed to be in the Besselian timescale, and epochs from 1984.0 onwards are assumed to be in the Julian timescale.
	www.bisque.com /Help/CCDSoft/afxcore/appendix_a_the_input_file.htm (976 words)

	How to Build a Calendar \| polysyllabic (Site not responding. Last check: 2007-10-31)
		It's called the "julian date" (important note: this is not the same thing as the Julian calendar), and it's the number astronomers use to date things.
		This epoch was calculated by Hillel II in the 4th century CE, but did not become universal practice until the end of the Middle Ages.
		The Julian calendar was a modification by Julius Caesar of the Republican calendar.
	www.polysyllabic.com /?q=buildacal (22261 words)

	slalink.4 (Site not responding. Last check: 2007-10-31)
		The epoch BEPOCH is strictly speaking Besselian, but if a Julian epoch is supplied the result will be affected only to a negligible extent.
		Conversion from Julian epoch 2000.0 to Besselian epoch 1950.0 only is provided for.
		It is the intention that FK5 should be a close approximation to an inertial frame, so that distant objects have zero proper motion; such objects have (in general) non-zero proper motion in FK4, and this routine returns those fictitious proper motions.
	hea-www.harvard.edu /SXG/starbase_infolinks/slalink.4.html (530 words)

	Astro Function Index
		Input is Julian Century (use JCJ2000()), output Nutation in Longitude.
		Input is Julian Century (use JCJ2000()), output Nutation in Obliquity.
		Input is Julian Century (use JCJ2000()), output Obliquity in degrees.
	www.pietro.org /Astro_Util_StaticDemo/FunctionIndex.htm (651 words)

	[No title] (Site not responding. Last check: 2007-10-31)
		Epochs of this form are ; often given in the astronomical literature as B1950.0 or J2000.0, ; but they can be different.
		Julian year numbers are measured in years whose ; lengths are exactly 365.25 days of 86400 second lengths.
		; ; MJD - if set, then Julian days are expressed as "modified" Julian ; Days, or Julian days minus 2400000.5d.
	cow.physics.wisc.edu /~craigm/idl/down/jbepoch.txt (256 words)

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