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Topic: Julian day

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Julian date

Julian calendar

Julian year

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Proleptic Gregorian calendar

Revised Julian calendar

Indiction cycle

Astronomical year numbering

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	Julian day - Wikipedia, the free encyclopedia
		The Modified Julian Day (MJD) is the number of days (with decimal fraction of the day) that have elapsed since midnight at the beginning of Wednesday November 17, 1858.
		Astronomers adopted Herschel's Julian Days in the late nineteenth century, but used the meridian of Greenwich instead of Alexandria, after the former was made the Prime Meridian by international conference in 1884.
		Julian days are typically used by astronomers to date astronomical observations, thus eliminating the complications resulting from using standard calendar periods like eras, years, months, or weeks.
	en.wikipedia.org /wiki/Julian_day (1937 words)

	Julian Day
		Julian Days are a way of reckoning the current date by a simple count of the number of days that have passed since some remote, arbitrary date.
		Julian Days are very useful because they make it easy to determine the number of days between two events by simply subtracting their Julian Day numbers.
		Julian Days can also be used to tell time; the time of day is expressed as a fraction of a full day, with 12:00 noon (not midnight) as the zero point.
	docs.kde.org /stable/en/kdeedu/kstars/ai-julianday.html (383 words)

	Boulder Community Network, Y2K, Julian and Gregorian Day Numbers
		The system of Julian days should not be confused with the simpler system of the same name which associates a date with the number of days elapsed since January 1st of the same year (according to which 2000-12-31 is day 366 ù of the year 2000).
		The Julian Day number system was invented by Joseph Justus Scaliger (born 1540-08-05 J in Agen, France, died 1609-01-21 J in Leiden, Holland), who during his life immersed himself in Greek, Latin, Persian and Jewish literature.
		Days are integer values in the range 1-31, months are integers in the range 1-12, and years are positive or negative integers.
	bcn.boulder.co.us /y2k/y2kbcalc.htm (1530 words)

	Julian Date Converter
		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.
		The omission of ten days of calendar dates was necessitated by the astronomical error built up by the Julian calendar over its many centuries of use, due to its too-frequent leap years.
	aa.usno.navy.mil /data/docs/JulianDate.html (570 words)

	Calendopaedia - The Julian Calender
		A day was accordingly taken from February and given to August; and in order that three months of thirty-one days might not come together, September and November were reduced to thirty days, and thirty-one given to October and December.
		The additional day which occurred every fourth year was given to February, being the shortest month, and was inserted in the calendar between the 24th and 25th day.
		February having then twenty-nine days, the 25th was the 6th of the calends of March, sexto calendas; the preceding, which was the additional or intercalary day, was called bis-sexto calendas,--hence the term bissextile, which is still employed to distinguish the year of 366 days.
	www.geocities.com /CapeCanaveral/Lab/7671/julian.htm (1229 words)

	Modified Julian Day Converter
		For Financial dates and legal dates, days between dates, days before a date or days after a date, day of the week for a given date in history, involving the last 2 centuries approximately, we suggest that you use our Julian to current day and date calculator.
		Julian Day Number is an integer counter of the days beginning at noon on January 1, 4713 B.C. (no, even though I may look like it, I was not there...), which is Julian Day Number 0.
		The Julian Date (as opposed to Julian Day) is the non-integer extension of the Day Number to include a real fraction of day, allowing a continuous time unit.
	www.csgnetwork.com /julianmodifdateconv.html (505 words)

	Julian Day
		The Julian day method was invented by Josefh Justus Scaliger and he named it "Julian" in honor of his father Julius Scaliger.
		Julian Ephemeris Day (JDE or JED) is the JD coresponds to an instant of time measured in the Terrestrial Dynamical Time scale.
		Sidereal Julian Day is Julian Day in which its days are sidereal days instead of mean solar days.
	wise-obs.tau.ac.il /~eran/Wise/Util/Julian_Day.html (148 words)

	Julian Date -- from Eric Weisstein's World of Astronomy
		The number of days since noon on January 1, -4712, i.e., January 1, 4713 BC (Seidelmann 1992).
		The first cycle was the 28 year period over which the Julian calendar repeats days of the week (the so-called solar number).
		Formulas for computing the Julian Date from year, month, and day in the Julian and Gregorian calendars are given below.
	scienceworld.wolfram.com /astronomy/JulianDate.html (394 words)

	Julian Day Numbers
		Julian Day Numbers, or the Julian Date (JD), is the absolute count of days that have elapsed since Noon 1 January 4713 BC on the Julian Calendar, or on what may more strictly be called the Julian "Proleptic" Calendar, meaning the Julian Calendar as applied to an era prior to its actual use.
		Thus, the Julian Day Number for 21 September 1997 on the Gregorian Calendar is 59 + 2,450,667 + -13 = 2,450,713.
		Since the Julian Day begins at Noon (the pre-1925 convention of the Astronomical or Nautical Day), the Day Number for the corresponding Civil Day may be obtained by substracting 0.5 = 2,450,765.5.
	www.friesian.com /numbers.htm (1559 words)

	Julian Real Estate - Harry Reese - Julian Information
		Julian is a mountain community of 3012 people located near the geographic center of San Diego County.
		Telephones started ringing in 1896, the first Apple Days was celebrated in 1909, the concrete road from Ramona reached town in 1926, electricity came in 1931, the water company formed in 1951, and it turned into the Julian Community Service District in 1965.
		Julian has always been a recreational area set in a saddle of the mountains between the coast and desert.
	www.julian-realestate.com /html/julian.html (1064 words)

	Julian day number and Julian period
		To set day one of the first Julian period, Scaliger calculated backwards to find the date on which all three of the cycles began on the same day (the beginning of the world?).
		The Julian Day number is not a measure of time; it is actually a unit of count, a count of days.
		It is often said that Scaliger named the Julian period after his father, but at the end of the introductory section to Book V of De Emendatione Temporum he explicitly states that he named his period after the Julian year.
	www.sizes.com /time/dayJulianr.htm (988 words)

	Astronomy Answers: Julian Day Number
		In astronomical formulas that contain a date, it is not convenient to write that date as a combination of years, months, and days, especially because not all years have the same number of days and not all months have the same number of days.
		Such information (the number of calendar years, months, and days) is not sufficient to calculate the exact number of days for all calendars, because not every year contains the same number of days as every other year, and not every month contains the same number of days as every other month (in all calendars).
		calendar days later than the first date (both in the same calendar, the Gregorian Calendar or the Jewish Calendar or the administrative Islamic Calendar), where you just subtract the year number, month number, and day number of the second date from those of the first date (which must be later).
	www.astro.uu.nl /~strous/AA/en/reken/juliaansedag.html (949 words)

	MODIFIED JULIAN DATE (via CobWeb/3.1 planetlab2.isi.jhu.edu) (Site not responding. Last check: 2007-10-22)
		In the case of the Julian day count, the name was given because at the time, the Julian calendar was in use and, therefore, the epoch of the day count was fixed in respect to it.
		Note that this day count conforms with the astronomical convention starting the day at noon, in contrast with the civil practice where the day starts with midnight (in popular use the belief is widespread that the day ends with midnight, but this is not the proper scientific use).
		The Julian Period is given by the time it takes from one coincidence to the next of a solar cycle (28), a lunar cycle (19), and the ancient Roman Indiction (a tax cycle of 15 years).
	tycho.usno.navy.mil.cob-web.org:8888 /mjd.html (919 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)).
		It is convenient for astronomers to use since it is not necessary to worry about odd numbers of days in a month, leap years, etc. Once you have the Julian Day Number of a particular date in history, it is easy to calculate time elapsed between it and any other Julian Day Number.
		This is the Julian Day Number for the beginning of the date in question at 0 hours, Greenwich time.
	quasar.as.utexas.edu /BillInfo/JulianDatesG.html (672 words)

	Date Algorithms - Julian Day Number - Implementation Examples (Site not responding. Last check: 2007-10-22)
		This can be shown to be an instance of our derived algorithm provided the Julian Day numbers is greater than or equal to 1867215.75, that is, for dates from February 29.25, 400 in the proleptic Gregorian calendar.
		This can be shown to be an instance of the previously derived algorithm provided the Julian Day numbers is greater than or equal to 1867215.75, that is, for dates from February 29.25, 400 in the proleptic Gregorian calendar.
		This algorithm is only valid for Julian Day numbers greater than or equal to -0.5, that is, dates from noon of January 1, -4712 in the proleptic Julian calendar.
	vsg.cape.com /~pbaum/date/injdimp.htm (1927 words)

	The Julian and Gregorian Calendars
		The difference of the length of the Julian calendar year from the length of the real solar year is thus 0.0078 days (11.23 minutes) in the former case and 0.0076 days (10.94 minutes) in the latter case.
		Ten days were omitted from the calendar, and it was decreed that the day following (Thursday) October 4, 1582 (which is October 5, 1582, in the old calendar) would thenceforth be known as (Friday) October 15, 1582.
		The number of days omitted determines the date for the Spring equinox, an omission of ten days resulting in a date usually of March 20th.
	www.hermetic.ch /cal_stud/cal_art.html (3479 words)

	Julian Day and Date Time Calculator
		For Financial dates and legal dates, days between dates, days before a date or days after a date, day of the week for a given date in history, involving the last 2 centuries, use the AutoSelect mode.
		In astronomy, a JD (Julian Date) is defined as the contiguous count of days from January 1, 4713 B.C., Greenwich Mean Noon (equal to zero hours UTC).
		Also day 1 was chosen as January 1, 4713 B.C. because the Julian Calendar, the Lunar Calendar and the Roman Tax Calendar all coincided.
	www.csgnetwork.com /juliandaydate.html (824 words)

	Julian Day Planner
		The Julian Day Planner generally tries to be amusing while providing a decimal time system for day-to-day scheduling of your time.
		The Julian Day system is a simple count of days (and fractions thereof) since noon on Monday, 1 January 4713 BCE on the Julian calendar.
		OS X Tiger Dashboard widget clock that shows the current Julian Day and fraction, as well as a decimal analog clock; the lit portion of the dial denotes the hours of sunlight.
	waxwolf.com /jdt (993 words)

	2. The Christian Calendar
		In the Julian calendar the relationship between the days of the week and the dates of the year is repeated in cycles of 28 years.
		In the Julian calendar, the Epact is the age of the moon on 22 March.
		The Lilian day number is similar to the Julian day number, except that Lilian day number 1 started at midnight on the first day of the Gregorian calendar, that is, 15 October 1582.
	www.tondering.dk /claus/cal/node3.html (7730 words)

	Julian date - a definition from Whatis.com (Site not responding. Last check: 2007-10-22)
		1) Not to be confused with the Julian calendar, a Julian date or day number is the number of elapsed days since the beginning of a cycle of 7,980 years invented by Joseph Scaliger in 1583.
		It is not certain whether the Julian date or day number system was named after Joseph Scaliger's father, Julius Caesar Scaliger, or after the Julian calendar.
		Julian day numbers are widely used in astronomy.
	whatis.techtarget.com /definition/0,,sid9_gci212429,00.html (332 words)

	PDC Live - Modified Julian Day
		Julian Day numbering was invented in 1583 by the French scholar, Joseph Justus Scaliger.
		Days are numbered consecutively from zero within the Julian Period, without any subdivisions in to months or years.
		Although small, the Julian Calendar's error of 0.0078 days per year mounted up over the centuries until by the late 1500s, the error was a noticeable 12 days.
	pdc.ro.nu /mjd.html (794 words)

	Julian Day
		The Julian Day Number (JD) is the time measured in units of days that have elapsed since 12 hours, January 1, 4713 BCE (in the Julian calendar) or November 24, -4713, 12:00:00 UTC in the Gregorian calendar extended backward in time.
		The Julian Day Number is named for Julius Scaliger, the father of Josephus Justus Scaliger, who invented the concept (not Julius Ceasar).
		Scaliger chose the particular date in the remote past because it was before recorded history and because in that year, three important cycles coincided with their first year of the cycle.
	home.att.net /~srschmitt/script_julian_day.html (321 words)

	Modified Julian Dates (Site not responding. Last check: 2007-10-22)
		Julian Day Number is an integer counter of the days beginning at noon 1 January 4713 B.C., which is Julian Day Number 0.
		The Julian Date is simply the extension of the Day Number to include a real fraction of day, allowing a continuous time unit.
		To convert Julian Dates to month/day/year you might wish to use the Julian Day Calculator, a Java-based program that was written by the folks at Numerical Recipes.
	bowie.gsfc.nasa.gov /time (269 words)

	koshko.com -- Rick Wiegmann Koshko's personal web site -- calendar section
		Jean Meeus, in his book Astronomical Algorithms, defines the Julian Day number as "a continuous count of days and fractions thereof from the beginning of the year -4712".
		In other words, Julian Day 0.0 corresponds to exactly 12 hours on January 1, 4712 BC under the Julian Calendar system when you include a zero year when extending the calendar deep into history.
		The Julian period has nothing to do with the Julian Calendar except that it follows the Julian Calendar's leap year rule (one leap year every four years without exception) when counting those 7,980 years.
	www.koshko.com /calendar/julian-day.shtml (497 words)

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