An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) Any of various systems for measuring and recording the passage of time by dividing the year into days, weeks, and months.
2) A table showing the months, weeks, and days in at least one specific year.
→ chronology.

M.E. calender, from O.Fr. calendier, from L. calendarium "account book," from kalendae "calends" the first day of the Roman month, from calare "to announce solemnly, call out," as the priests did in proclaiming the new moon that marked the calends, from PIE base *kele- "to call, shout" (cf. Skt. usakala "cock," lit. "dawn-calling;" Gk. kaleo "to call," kelados "noise," kledon "report, fame;" O.H.G. halan, O.N. kalla "to call;" O.E. hlowan "to low;" Lith. kalba "language").

Gâhšomâr, gâhšomâri, gâhmâr from gâh "time," Mid.Pers. gâh, gâs, + šomâr, mâr "reckoning," → calculate.
Sâlnâmé, from sâl, → year, + nâmé "a writing, letter, book."

A period of 24 hours, from one midnight to the following midnight.

→ calendar; → day.

One of the periods into which a calendar is divided, ordinarily 12, but in earlier systems 10 (the first Roman calendar under Romulus) or 13 (ancient Iranian calendar using a month intercalation).

→ calendar; → month.

The time interval between the new year's day in a given calendar system and the day before the following new year's day. In the Gregorian system the calendar year begins on January 1 and ends on December 31. In the Iranian calendar it begins on Farvardin 1, the day closest to the spring equinox and ends on Esfand 29 or 30.

→ calendar; → year.

A → lunisolar calendar (Chinese: yīnyáng li), which is now mainly used for determining cultural festivals. It is based on astronomical observations of the Sun's annual apparent motion (→ ecliptic) and → lunar phases. The calendar starts at Chinese New Year and consists of 12 or 13 → lunar months. The ecliptic is divided into 24 sections (jiéqi) of 15° each. In general, Chinese New Year falls on the day of the second new Moon after the → winter solstice on approximately December 22. Since 12 months are about 11 days shorter than the → tropical year, a → leap month is inserted to keep the calendar in tune with the seasons. An ordinary → lunar year has 353-355 days while a → leap year has 383-385 days. Therefore, the → solstices and → equinoxes move 11 (or 10 or 12) days later. Each 13-month leap year is about 19 days too long, so the solstices and equinoxes jump 19 (or 18 or 20) days earlier. Each year is assigned a name consisting of two components within a 60-year cycle. The first component is a celestial stem. The second component is a terrestrial branch; it features the names of animals in a zodiac cycle consisting of 12 animals. Each of the two components is used sequentially. Therefore, the first year of the 60-year cycle becomes jia-zi, the second year is yi-chou, and so on. One starts from the beginning when the end of a component is reached. The 60th year is gui-hai. The current 60-year cycle started on 2 February 1984. The leap year must be inserted if there are 13 new moons from the start of the 11th month in the first year to the start of the 11th month in the second year. The beginnings of the Chinese calendar can be traced back to the 14th century BC. Legend has it that the Emperor Huang-di invented the calendar in 2637 BC. The calendar has been adopted by several southeast Asian cultures. The Chinese calendar has undergone several reforms, the last one in 1645. For more details, see, e.g., Helmer Aslaksen, The Mathematics of the Chinese calendar, e-paper.

Chinese adj. of China, from Pers. Cin [Chin], from Qin the first imperial dynasty of China (221 to 206 BC); → calendar.

A → lunisolar calendar in which the years are named after each of the following twelve animals: rat, ox, tiger, hare, dragon, snake, horse, sheep, monkey, cock, dog, pig. An animal presides over one year in the twelve-year cycle, which is then repeated. The calendar was/is mainly used by central Asian cultures (Khotanese, Sogdians, Buddhists, Kucheans, Mongols, and Chinese). It was also used in Iran after the Mongol invasion in the thirteenth century.

→ duodecennial; → animal; → calendar.

A calendar composed by Fabre d'Eglantine and others during the French Revolution which divided the year into 12 months of 30 days each, with five odd days called → Sansculottides. The year started at → autumnal equinox and the months were: Vendémiaire (Vintage), Brumaire (Fog), Frimaire (Frost), Nivôse (Snow), Pluviôse (Rain), Ventôse (Wind), Germinal (Buds), Floréal (Flowers), Prairial (Meadows), Messidor (Harvest), Termidor (Heat), Fructidor (Fruits). The week consisted of 10 days, and was called a Décade; each 10th day of Décade (called Décadi) was a day of rest. The calendar was used by the French government for about 12 years, from late 1793 to 1805, when it was suppressed by Napoleon.

M.E. Frensh, French, O.E. Frencisc "of the Franks," from Frank; republican, from republic, from Fr. république, from L. respublica, from res publica "public interest, the state," from res "affair, matter, thing" + publica, feminine of publicus "public;" → calendar.

A → solar calendar in which the year length is assumed to be 365.2425 solar days. It is now used as the civil calendar in most countries. The Gregorian calendar is a revision of the → Julian calendar instituted in a papal bull by Pope Gregory XIII in 1582. The reason for the calendar change was to correct for drift in the dates of significant religious observations (primarily Easter) and to prevent further drift in the dates.

Named after Pope Gregory XIII (1502-1585), an Italian, born Ugo Boncompagni, Pope from 1572 to 1585, who ordered the reform of the Julian calendar; → calendar.

A → lunisolar calendar used by Jews for religious purposes. The year consists of 12 months alternating between 29 and 30 days, making a year of 354 days. In order to conform to the → solar year, a → leap month is included every third year. A month begins the day the new moon is first seen. The years are counted from the time of "creation," believed by Jewish theologians to have occurred in the year 3761 B.C. Also called → Jewish calendar.

Hebrew, from O.E., from O.Fr. Ebreu, from L. Hebraeus, from Gk. Hebraios, from Aramaic 'ebhrai, corresponding to Heb. 'ibhri "an Israelite," literally "one from the other side," in reference to the River Euphrates, or perhaps simply denoting "immigrant;" from 'ebher "region on the other or opposite side;" → calendar.

Gâhšomâr, → calendar; yahud→ Jewish calendar.

The most accurate solar calendar in use, which is based on two successive passages of the Sun through the true vernal equinox. The year length, defined by an ingenious intercalation system devised by the mathematician Omar Khayyâm (A.D. 1048-1131), is 365.2424.. solar days, in perfect agreement with the → vernal-equinox year of 365.24236 solar days (epoch +2000). This interval should not be confounded with the → tropical year of 365.2422 solar days. The most remarkable feature of the calendar is Nowruz, the spring festival, which has its profound roots in the Zoroastrian worldview. Same as → Persian calendar. Click here for more details.

Iranian, of or pertaining to Iran "(land of) the Aryans," as below; → calendar.

Gâhšomâr, → calendar; Irâni adj. of Irân, from Mid.Pers. Êrân "(land of) the Aryans," pluriel of êr "noble, hero," êrîh "nobility, good conduct;" Parthian Mid.Pers. aryân; O.Pers. ariya- "Aryan;" Av. airya- "Aryan;" cf. Skt. ārya- "noble, honorable, respectable."

A religious and strictly → lunar calendar which follows the visibility of the lunar crescent after → conjunction and ignores the seasons (see also → synodic month). The year, which consists of 12 months of 29 or 30 days, is approximately 354 days long (→ lunar year of 354.3672 days). Because the calendar follows a purely lunar cycle, each month begins 10 or 11 days earlier each year in relation to the 365-day → solar year. As a result, the cycle of 12 lunar months regresses through the seasons over a period of 33 years. For religious purposes, Muslims begin the months with the first visibility of the lunar crescent. The month length may be 30 or 29 days during four or three successive months respectively. However, astronomers consider a calendar with months of alternately 30 and 29 days. The 33-year period contains 11 → leap years of 355 days. The origin of the Islamic era is considered to be the migration (Hijra) of Prophet Muhammad from Mecca to Medina on 16 July, A.D. 622. It was Caliph Umar (died 644) who, 17 years after the actual event, poised the migration as the beginning of the Muslim era.

From Islam, literally "submission" (to God); → calendar.

An Iranian solar calendar, based on two successive passages of the Sun through the true → vernal equinox. It results from a reform undertaken by a group of astronomers led by Omar Khayyam (A.D. 1048-1131). The current → Iranian calendar is an improved version of the Jalali calendar.

Jalali, from the name of the ruler Jalâleddin Malek Šâh of the Saljuqid dynasty, who ordered the reform; → calendar.

Same as → Hebrew calendar

Jewish, adj. of jew, from M.E. jewe, giu, gyu, ju, from O.Fr. juiu, juieu, gyu, from L.L. judeus, from L. juaeus, from Gk. ioudaios, from Aramaic yehudhai, from Heb. yəhudhi "Jew," from Yəhudah "Judah," literally "celebrated," name of Jacob's fourth son and of the tribe descended from him; → calendar.

Gâhšomâr→ calendar; yahud, from Ar., from Heb., as above.

A → solar calendar established by Julius Caesar in 46 B.C. to replace the → Roman calendar. It was inspired by the Egyptian calendar year of 365 days. The astronomer Sosigenes set up the months (January to December) and added an extra day in February every fourth year (→ leap year). This gave an average year of 365.25 days. The Julian calendar remained unchanged for 1,600 years, and was replaced by the → Gregorian calendar to correct its errors. The Roman calendar before the reform was running 80 days out of alignment with the seasons of a true year. Sosigenes fixed the calendar by having 445 days in the year 46 B.C., which brought the seasons in line with the calendar. The year 45 B.C. is known as the first leap year of the Julian calendar. However, Sosigenes' work was misinterpreted and they were placing leap years every 3 years instead of every 4 years.

Julian, adj. of L. Julius.

A calendar that is based on the cycles of the → lunar phase and involves the → lunar month and → lunar year. For example → Islamic calendar, → Vietnamese lunar calendar.

→ lunar; → calendar.

A calendar in which the → solar year consists of 12 or 13 lunar → synodic months. Lunisolar calendars are → solar calendars, but use the lunar month as the basic unit rather than the → solar day. The 13th → embolismic month is to keep lunar and solar cycles in pace with each other. The reason is that the solar year has about 365 days, but 12 lunar months amount to 354 days, which is about 11 days short of a year. The most well-known lunisolar calendars are the Babylonian, Hebrew, and Chinese.

From luni-, from → lunar, + → solar; → calendar.

A special calendar for time reckoning on Mars in which the year consists of 668 → sols (687 Earth days) and each sol has 24h 39m 35s. For convenience, sols are divided into a 24-hour clock. Each landed Mars mission keeps track of local solar time at its landing site, which depends upon the lander's longitude of Mars. The Martian year begins when Mars arrives at the → vernal point of the orbit in its northward journey; in other words, when the solar longitude Ls is 0°. Mars' other seasons begin when Ls = 90° at → summer solstice, 180° at → autumn equinox, and 270° at → winter solstice. The year counts begin at Mars Year 1, at the northern → vernal equinox of April 11, 1955. The second half of that year was marked by a major dust storm (→ Mars' dust storm). February 7, 2021 marked the start of Year 36 on Mars. Year 37 will start on Dec. 26, 2022, and Year 38 on Nov. 12, 2024. On Earth, spring, summer, autumn, and winter are all similar in length, because Earth's orbit is nearly circular (→ eccentricity = 0.0167), so it moves at nearly constant speed around the Sun. By contrast, Mars' elliptical orbit (→ eccentricity = 0.0934) makes its distance from the Sun change with time, and also makes it speed up and slow down in its orbit. Mars is at → aphelion (249,200,000 km from Sun) at Ls = 70°, near the northern summer solstice, and at → perihelion (206,700,000 km) at Ls = 250°, near the southern summer solstice. The Mars dust storm season begins just after perihelion at around Ls = 260°.

→ Mars; → calendar.

A complex calendar created by the ancient central American Mayas which uses three different dating systems in parallel: Long Count, Tzolkin, and Haab. Only Haab has a direct relationship with the length of the year. It is a solar → vague year consisting of 18 months of 20 days each, and an additional period of 5 → epagomenal days. Tzolkin is a calendar of 13 x 20 = 260 days running within Haab and is used for ritual purposes. A date is usually described by specifying its position in both the Tzolkin and Haab calendars. The least common multiple of the two calendars, called the Calendar Round, has 18,980 days, representing a cycle of 73 sacred years, or 52 vague years. The Long Count is the number of days since the start of the Maya era. There is disagreement about the beginning date of the Long Count. Most authorities agree, however, that the Long Count started in 3114 B.C., with several possible dates.

Maya, proper name; → calendar.

A chart or mechanical device that indicates the day of the week for any given date over a period of many years.

→ perpetual; → calendar.

Same as → Iranian calendar.

Persian, adj. of Persia, from O.Pers. Pārsa.

Irâni adj. of Irân, from Mid.Pers. Êrân "(land of) the Aryans," pluriel of êr "noble, hero," êrîh "nobility, good conduct;" Parthian Mid.Pers. aryân; O.Pers. ariya- "Aryan;" Av. airya- "Aryan;" cf. Skt. ārya- "noble, honorable, respectable."