What type of calendar does the us use

But Protestant countries were wary of this new popish initiative, seeing it as a suspicious Catholic intrusion. When they finally did, they had to erase 11 days. Sweden only made the change in Turkey was split between the Julian and Islamic calendars until During the French Revolution, meanwhile, leaders in France decided to purge their calendars of any religious overtones.

The new French Republican calendar , adopted in , had 12 identical months of 30 days. Weeks had 10 days in them. And there were five or six extra days at the end of each year for holidays.

The calendar also renamed the months, with monikers like Brumaire or Thermidor. That funky calendar, alas, was abandoned in and only revived briefly by the Paris Commune in Nowadays, the Gregorian calendar has largely conquered the world, and most countries now follow it for coordination purposes.

Saudi Arabia just switched over this month from the Islamic calendar, since the elimination of 11 days would help save money on civil servant pay for the budget-crunched kingdom.

The Eastern Orthodox Church, meanwhile, still follows a version of the Julian calendar — which means that Christmas falls 13 days later than in the Gregorian calendar. The Gregorian calendar also has a bunch of oddities.

Unlike the French Republican calendar, our months are uneven, some 31 days, some 30, plus the monstrosity that is February.

Some reformers have suggested we change the calendar to correct these blemishes. At Johns Hopkins University, Steve Hanke and Richard Henry have proposed the Hanke-Henry Permanent Calendar , which would have days every year plus a "leap week" tacked on every five or six years to adjust for the error. The advantage here, they say, is that the calendar would be the same every year. October 4 would always fall on a Wednesday, for instance.

No need for confusing updates to calendars. If worst comes to worst, we can always convene again in and remove that pesky day. We also have leap seconds to contend with. It technically takes Earth a bit longer than 24 hours to complete a full rotation: 86, So in order to keep our clocks matched up with solar noon, when the sun is highest in the sky, a leap second gets added every few years.

This calendar is the official calendar of Israel and is the liturgical calendar of the Jewish faith. In principle the beginning of each month is determined by a tabular New Moon molad that is based on an adopted mean value of the lunation cycle.

To ensure that religious festivals occur in appropriate seasons, months are intercalated according to the Metonic cycle, in which lunations occur in nineteen years. By tradition, days of the week are designated by number, with only the seventh day, Sabbath, having a specific name.

Days are reckoned from sunset to sunset, so that day 1 begins at sunset on Saturday and ends at sunset on Sunday. The Sabbath begins at sunset on Friday and ends at sunset on Saturday. Years are counted from the Era of Creation, or Era Mundi, which corresponds to October 7 on the Julian proleptic calendar. Each year consists of twelve or thirteen months, with months consisting of 29 or 30 days. An intercalary month is introduced in years 3, 6, 8, 11, 14, 17, and 19 in a nineteen-year cycle of lunations.

The initial year of the calendar, A. Anno Mundi 1, is year 1 of the nineteen-year cycle. The calendar for a given year is established by determining the day of the week of Tishri 1 first day of Rosh Hashanah or New Year's Day and the number of days in the year.

Years are classified according to the number of days in the year see Table 3. Table 3. Tishri 30 7. Nisan 30 2. Iyar 29 3. Sivan 30 4. Tevet 29 Tammuz 29 5. Shevat 30 Av 30 6. Full male month: a month comprising 30 days. Ordinary year: a year comprising 12 months, with a total of , , or days. Leap year: a year comprising 13 months, with a total of , , or days.

Complete year shelemah : a year in which the months of Heshvan and Kislev both contain 30 days. Deficient year haser : a year in which the months of Heshvan and Kislev both contain 29 days. Regular year kesidrah : a year in which Heshvan has 29 days and Kislev has 30 days. Halakim singular, helek : "parts" of an hour; there are halakim per hour. Molad plural, moladot : "birth" of the Moon, taken to mean the time of conjunction for modern calendric purposes. Dehiyyah plural, dehiyyot : "postponement"; a rule delaying 1 Tishri until after the molad.

The months of Heshvan and Kislev vary in length to satisfy requirements for the length of the year see Table 3.

For calendrical calculations, the day begins at 6 P. Terminology is explained in Table 3. Calendrical calculations are referred to the meridian of Jerusalem -- 2 hours 21 minutes east of Greenwich. Rules for constructing the Hebrew calendar are given in the sections that follow. Cohen , Resnikoff , and Spier provide reliable guides to the rules of calculation. This is determined by the day of the Tishri molad and the four rules of postponements dehiyyot.

The dehiyyot can postpone Tishri 1 until one or two days following the molad. Tabular new moons maladot are reckoned from the Tishri molad of the year A. The adopted value of the mean lunation is 29 days, 12 hours, halakim To avoid rounding and truncation errors, calculation should be done in halakim rather than decimals of a day, since the adopted lunation constant is expressed exactly in halakim. Lunation constants required in calculations are shown in Table 3.

By subtracting off the weeks, these constants give the shift in weekdays that occurs after each cycle. The dehiyyot are as follows: a If the Tishri molad falls on day 1, 4, or 6, then Tishri 1 is postponed one day. If this causes Tishri 1 to fall on day 1, 4, or 6, then Tishri 1 is postponed an additional day to satisfy dehiyyah a. Dehiyyah b is an artifact of the ancient practice of beginning each month with the sighting of the lunar crescent.

It is assumed that if the molad i. Dehiyyah c prevents an ordinary year from exceeding days. If the Tishri molad of an ordinary year occurs on Tuesday at or after A. According to dehiyyah b , Tishri 1 of the next year must be postponed to Sunday, which by dehiyyah a occasions a further postponement to Monday. This results in an ordinary year of days. Postponing Tishri 1 from Tuesday to Thursday produces a year of days. Dehiyyah d prevents a leap year from falling short of days.

Therefore, by dehiyyot b and a , Tishri 1 beginning the leap year was postponed to Thursday. To prevent a leap year of days, dehiyyah d postpones by one day the beginning of the ordinary year. A thorough discussion of both the functional and religious aspects of the dehiyyot is provided by Cohen The number of excess days identifies the year as being deficient, regular, or complete, respectively.

A leap year consists of 54 weeks plus 5, 6, or 7 days, which again are designated deficient, regular, or complete, respectively. The length of a year can therefore be determined by comparing the weekday of Tishri 1 with that of the next Tishri 1. First consider an ordinary year. The weekday shift after twelve lunations is For example if a Tishri molad of an ordinary year occurs on day 2 at 0 hours 0 halakim 6 P.

The first Tishri molad does not require application of the dehiyyot , so Tishri 1 occurs on day 2. Because of dehiyyah a , the following Tishri 1 is delayed by one day to day 7, five weekdays after the previous Tishri 1. Since this characterizes a complete year, the months of Heshvan and Kislev both contain 30 days. The weekday shift after thirteen lunations is If the Tishri molad of a leap year occurred on day 4 at 20 hours halakim , the next Tishri molad will occur on day 3 at 18 hours 9 halakim.

Becuase of dehiyyot b , Tishri 1 of the leap year is postponed two days to day 6. Because of dehiyyot c , Tishri 1 of the following year is postponed two days to day 5. This six-day difference characterizes a regular year, so that Heshvan has 29 days and Kislev has 30 days. At that time the patriarch Hillel II, breaking with tradition, disseminated rules for calculating the calendar. Prior to that time the calendar was regarded as a secret science of the religious authorities.

The exact details of Hillel's calendar have not come down to us, but it is generally considered to include rules for intercalation over nineteen-year cycles. Up to the tenth century A. Information on calendrical practices prior to Hillel is fragmentary and often contradictory. The earliest evidence indicates a calendar based on observations of Moon phases. Since the Bible mentions seasonal festivals, there must have been intercalation. There was likely an evolution of conflicting calendrical practices.

The Babylonian exile, in the first half of the sixth century B. This is visible today in the names of the months. The Babylonian influence may also have led to the practice of intercalating leap months. During the period of the Sanhedrin, a committee of the Sanhedrin met to evaluate reports of sightings of the lunar crescent. If sightings were not possible, the new month was begun 30 days after the beginning of the previous month. Decisions on intercalation were influenced, if not determined entirely, by the state of vegetation and animal life.

Although eight-year, nineteen-year, and longer- period intercalation cycles may have been instituted at various times prior to Hillel II, there is little evidence that they were employed consistently over long time spans.

Return to Index to Calendars 4. The Islamic Calendar The Islamic calendar is a purely lunar calendar in which months correspond to the lunar phase cycle. As a result, the cycle of twelve lunar months regresses through the seasons over a period of about 33 years. For religious purposes, Muslims begin the months with the first visibility of the lunar crescent after conjunction. For civil purposes a tabulated calendar that approximates the lunar phase cycle is often used. The seven-day week is observed with each day beginning at sunset.

Weekdays are specified by number, with day 1 beginning at sunset on Saturday and ending at sunset on Sunday. Day 5, which is called Jum'a, is the day for congregational prayers. Unlike the Sabbath days of the Christians and Jews, however, Jum'a is not a day of rest. Jum'a begins at sunset on Thursday and ends at sunset on Friday.

This epoch, 1 A. This is called the astronomical Hijra epoch. Chronological tables e. In both cases the Islamic day begins at sunset of the previous day. For religious purposes, each month begins in principle with the first sighting of the lunar crescent after the New Moon. This is particularly important for establishing the beginning and end of Ramadan. Because of uncertainties due to weather, however, a new month may be declared thirty days after the beginning of the preceding month.

Although various predictive procedures have been used for determining first visibility, they have always had an equivocal status. In practice, there is disagreement among countries, religious leaders, and scientists about whether to rely on observations, which are subject to error, or to use calculations, which may be based on poor models. Chronologists employ a thirty-year cyclic calendar in studying Islamic history. In this tabular calendar, there are eleven leap years in the thirty-year cycle.

Odd-numbered months have thirty days and even-numbered months have twenty-nine days, with a thirtieth day added to the twelfth month, Dhu al-Hijjah see Table 4. Years 2, 5, 7, 10, 13, 16, 18, 21, 24, 26, and 29 of the cycle are designated leap years. This type of calendar is also used as a civil calendar in some Muslim countries, though other years are sometimes used as leap years.

The mean length of the month of the thirty-year tabular calendar is about 2. Table 4. Safar 29 8. Sha'ban 29 3. Rabi'a I 30 9. Rabi'a II 29 Shawwal 29 5. Jumada I 30 Jumada II 29 This was a departure from the lunisolar calendar commonly used in the Arab world, in which months were based on first sightings of the lunar crescent, but an intercalary month was added as deemed necessary.

It is not known how the initial date was determined. However, calculations show that the astronomical New Moon i. Return to Index to Calendars 5. The Indian Calendar As a result of a calendar reform in A. However, the initial epoch is the Saka Era, a traditional epoch of Indian chronology. Months are named after the traditional Indian months and are offset from the beginning of Gregorian months see Table 5.

In addition to establishing a civil calendar, the Calendar Reform Committee set guidelines for religious calendars, which require calculations of the motions of the Sun and Moon. Tabulations of the religious holidays are prepared by the India Meteorological Department and published annually in The Indian Astronomical Ephemeris.

Despite the attempt to establish a unified calendar for all of India, many local variations exist. The Gregorian calendar continues in use for administrative purposes, and holidays are still determined according to regional, religious, and ethnic traditions Chatterjee, Normal years have days; leap years have In a leap year, an intercalary day is added to the end of Caitra.

To determine leap years, first add 78 to the Saka year. If this sum is evenly divisible by 4, the year is a leap year, unless the sum is a multiple of In the latter case, the year is not a leap year unless the sum is also a multiple of Table 5. Vaisakha 31 Vaisakha 1 April 21 3. Jyaistha 31 Jyaistha 1 May 22 4. Asadha 31 Asadha 1 June 22 5. Sravana 31 Sravana 1 July 23 6. Bhadra 31 Bhadra 1 August 23 7.

Asvina 30 Asvina 1 September 23 8. Kartika 30 Kartika 1 October 23 9. Agrahayana 30 Agrahayana 1 November 22 Pausa 30 Pausa 1 December 22 Magha 30 Magha 1 January 21 Most holidays occur on specified lunar dates tithis , as is explained later; a few occur on specified solar dates.

The calendrical methods presented here are those recommended by the Calendar Reform Committee They serve as the basis for the calendar published in The Indian Astronomical Ephemeris.

However, many local calendar makers continue to use traditional astronomical concepts and formulas, some of which date back years. The Calendar Reform Committee attempted to reconcile traditional calendrical practices with modern astronomical concepts.

According to their proposals, precession is accounted for and calculations of solar and lunar position are based on accurate modern methods. All astronomical calculations are performed with respect to a Central Station at longitude 82o30' East, latitude 23o11' North. For religious purposes solar days are reckoned from sunrise to sunrise. A solar month is defined as the interval required for the Sun's apparent longitude to increase by 30o, corresponding to the passage of the Sun through a zodiacal sign rasi.

The initial month of the year, Vaisakha, begins when the true longitude of the Sun is 23o 15' see Table 5. Because the Earth's orbit is elliptical, the lengths of the months vary from The short months all occur in the second half of the year around the time of the Earth's perihelion passage.

Duration Approx. However, several countries, including the US and Canada, count Sunday as the first day of the week. The Gregorian calendar's predecessor, the Julian Calendar , was replaced because it was too inaccurate. It did not properly reflect the actual time it takes the Earth to orbit once around the Sun, known as a tropical year.

The Julian calendar's formula to calculate leap years produced a leap year every four years. This is too often, and eventually, the Julian calendar was several days out of sync with the fixed dates for astronomical events like equinoxes and solstices.

The introduction of the Gregorian calendar allowed for the realignment with events like the vernal equinox and winter solstice. The Gregorian calendar was first adopted in Italy, Poland, Portugal, and Spain in , and included the following changes:.

In Europe's Protestant countries, however, people feared that the new calendar was an attempt by the Catholic Church to silence their movement.