Information AboutMonth |
|
The month is a unit of Time , used with Calendar s, which is approximately as long as some natural Period related to the motion of the Moon . The traditional concept arose with the cycle of Moon Phase s; such months (lunations) are ''synodic'' months and last ~29.53 Day s. From Excavated Tally Stick s, researchers have deduced that people counted days in relation to the Moon's phases as early as the Paleolithic age. Synodic months are still the basis of many calendars. Astronomical background The motion of the Moon in its Orbit is very complicated and its period is not constant. Moreover, many cultures (most notably those using the ancient Hebrew (Jewish) Calendar and the Islamic Calendar ) start a month with the first appearance of the thin crescent of the New Moon after sunset over the western horizon. The date and time of this actual observation depends on the exact geographical longitude as well as latitude, atmospheric conditions, the visual acuity of the observers, etc. Therefore the beginning and lengths of months in these calendars can not be accurately predicted. Most Jews currently follow a precalculated calendar, but the Karaites rely on actual moon observations. Sidereal month The actual period of the Moon's orbit as measured in a fixed frame of reference is known as a ''sidereal'' month, because it is the time it takes the Moon to return to the same position on the s, characterized by Asterism s (apparent groups of stars), one for each day that the Moon follows its track among the stars. Tropical month It is customary to specify positions of celestial bodies with respect to the vernal of the Sun . Anomalistic month Like all orbits, the Moon's is an ellipse rather than a circle. However, the orientation (as well as the shape) of this orbit is not fixed. In particular, the position of the extreme points (the line of the and Apogee ), makes a full circle in about nine years. It takes the Moon longer to return to the same apsis because it moved ahead during one revolution. This longer period is called the ''anomalistic'' month, and has an average length of 27.554 551 days (27 d 13 h 18 min 33.2 s), or about 27 1/2 days. The apparent diameter of the Moon varies with this period, and therefore this type of month has some relevance for the prediction of Eclipse s (see Saros ), whose extent, duration, and appearance (whether total or annular) depend on the exact apparent diameter of the Moon. The apparent diameter of the Full Moon varies with the Full Moon Cycle which is the beat period of the synodic and anomalistic month, and also the period after which the apsides point to the Sun again. Draconic month The orbit of the Moon lies in a plane that is tilted with respect to the plane of the is possible. The "draconic/draconitic" month refers to the mythological dragon that lives in the nodes and regularly eats the Sun or Moon during an eclipse. Synodic month The cause of Moon Phase s is that from the Earth we see the part of the Moon that is illuminated by the Sun from different angles as the Moon traverses its orbit. So the appearance depends on the position of the Moon with respect to the Sun (as seen from the Earth). Because the Earth orbits the Sun, it takes the Moon extra time (after completing a sidereal month, i. e. a full circle) to catch up and return to the same position with respect to the Sun. This longer period is called the ''synodic'' month (from Greek ''syn hodô'' or σὺν ὁδῴ, meaning "with the way", i. e. the Moon travelling with the Sun). Because of the perturbations of the orbits of the Earth and Moon, the actual time between Lunation s may range from about 29.27 to about 29.83 days. The long-term average duration is 29.530 588 days (29 d 12 h 44 min 2.8 s), or about 29 ½ days. Month lengths Here is a list of the average length of the various astronomical lunar months Derived from ELP2000-85: M. Chapront-Touzé, J. Chapront (1991): ''Lunar tables and programs from 4000 B. C. to A. D. 8000''. Willmann-Bell, Richmond VA; ISBN 0-943396-33-6. These are not constant, so a first-order (linear) approximation of the secular change is provided: Valid for the epoch ): ''Note:'' time expressed in Ephemeris Time (more precisely Terrestrial Time ) with days of 86400 SI Second s. y is years since the epoch (2000), expressed in Julian years of 365.25 days. Note that for calendrical calculations, one would probably use days measured in the time scale of Universal Time , which follows the somewhat unpredictable rotation of the Earth, and progressively accumulates a difference with ephemeris time called ΔT . Calendrical consequences For more details on this topic, see Lunar Calendar and Lunisolar Calendar . At the simplest level, all lunar calendars are based on the approximation that 2 lunations last 59 days: a 30 day full month followed by a 29 day '''hollow month''' — but this is only marginally accurate and quickly needs correction by using larger cycles, or the equivalent of Leap Day s. Second, the synodic month does not fit easily into the Year , which makes constructing accurate, rule-based lunisolar calendars difficult. The most common solution to this problem is the Metonic Cycle , which takes advantage of the fact that 235 lunations are approximately 19 Tropical Year s (which add up to not quite 6940 days). However, a Metonic calendar (such as the Hebrew Calendar ) will drift against the seasons by about 1 day every 200 years. The problems of creating reliable lunar calendars may explain why Solar Calendar s, having months which no longer relate to the phase of the moon, and being based only on the more predictable motion of the sun against the sky, have generally replaced lunar calendars for civil use in most societies. Months in various calendars Julian and Gregorian calendars The Gregorian Calendar , like the Julian Calendar before it, has twelve months: # January , 31 Day s # February , 28 days, 29 in Leap Year s, or 30 on Certain Occasions In Related Calendars # March , 31 days # April , 30 days # May , 31 days # June , 30 days # July , 31 days # August , 31 days # September , 30 days # October , 31 days # November , 30 days # December , 31 days For the rationale behind the unusual day lengths, see February and August . Months existing in the Roman Calendar in the past include:
The famous Mnemonic '' Thirty Days Hath September '' is the most common way of teaching the lengths of the months. You can also use the knuckles of the four fingers of your hand and the spaces between them to remember the lengths of the months. First make a fist, then begin listing each month as you proceed across your hand. All months landing on a knuckle are 31 days long and those landing between them are not (it's up to you to figure out February). When you reach the knuckle of your little finger (July), go back to the first knuckle and continue with August. French Republican Calendar This calendar was proposed during the French Revolution, and used by the French government for about twelve years from late 1793. There were twelve months of 30 days each, grouped into three ten-day weeks called ''décades''. The five or six extra days needed to approximate the tropical year were placed after the months at the end of each year. A period of four years ending on a leap day was to be called a ''Franciade''. It began at the autumn equinox:
# Vendémiaire # Brumaire # Frimaire
# Nivôse # Pluviôse # Ventôse
# Germinal # Floréal # Prairial
# Messidor # Thermidor # Fructidor Islamic calendar There are also twelve months in the Islamic Calendar . They are named as follows: # Muharram Ul Haram (or shortened to Muharram) محرّم # Safar صفر # Rabi`-ul-Awwal (Rabi' I) ربيع الأول # Rabi`-ul-Akhir (or Rabi` al-THaany) (Rabi' II) ربيع الآخر أو ربيع الثاني # Jumaada-ul-Awwal (Jumaada I) جمادى الأول # Jumaada-ul-Akhir (or Jumaada al-THaany) (Jumaada II) جمادى الآخر أو جمادى الثاني # Rajab رجب # Sha'aban شعبان # Ramadhan رمضان # Shawwal شوّال # Dhul Qadah ذو القعدة (or Thw al-Qi`dah) # Dhul Hijja ذو الحجة (or Thw al-Hijjah) For details, please see Islamic Calendar . Hebrew Calendar The Hebrew Calendar has 12 or 13 months. # Nisan , 30 days # Iyyar , 29 days # Sivan , 30 days # Tammuz , 29 days # Av , 30 days # Elul , 29 days # Tishri , 30 days # Heshvan , 29/30 days # Kislev , 29/30 days # Tevet , 29 days # Shevat , 30 days # Adar 1 , 30 days, Intercalary month # Adar 2 , 29 days Adar 1 is only added in leap years. In ordinary years, Adar 2 is simply called Adar. Hindu Calendar The Hindu Calendar has various systems of naming the months. The months in the lunar calendar are: # Chaitra # Vaishaakha # Jyaishtha # Aashaadha # Shraavana # Bhaadrapada # Aashvayuja # Kaartika # Maargashiirsha # Pausha # Maagha # Phaalguna These are also the names used in the Indian National Calendar for the newly redefined months. The names in the solar calendar are just the names of the Zodiac sign in which the sun travels. They are # Mesha # Vrishabha # Mithuna # Kataka # Simha # Kanyaa # Tulaa # Vrishcika # Dhanus # Makara # Kumbha # Miina Iranian/Persian calendar The Iranian / Persian Calendar , currently used in Iran and Afghanistan , also has 12 months. The Persian names are included in the parentheses. # Farvardin (فروردین), 31 days # Ordibehesht (اردیبهشت), 31 days # Khordad (خرداد), 31 days # Tir (تیر), 31 days # Mordad (مرداد), 31 days # Shahrivar (شهریور), 31 days # Mehr (مهر), 30 days # Aban (آبان), 30 days # Azar (آذر), 30 days # Dey (دی), 30 days # Bahman (بهمن), 30 days # Esfand (اسفند), 29 days, 30 in leap years Icelandic/Old Norse calendar The old Icelandic calendar is not in official use anymore, but some holidays and annual feasts are still calculated according to it in Iceland. It has 12 months, broken down into two groups of six.
# Gormánuður (mid October - mid November, "slaughter month" or " Gór 's month") # Ýlir (mid November - mid December, " Yule month") # Mörsugur (mid December - mid January, "fat sucking month") # Þorri (mid January - mid February, "frozen snow month") # Góa (mid February - mid March, "Góa's month, see Nór ") # Einmánuður (mid March - mid April, "lone" or "single month")
# Harpa (mid April - mid May, Harpa is a female name, probably a forgotten goddess, first day of Harpa is celebrated as Sumardagurinn Fyrsti ) # Skerpla (mid May - mid June, another forgotten goddess) # Sólmánuður (mid June - mid July, " Sun month") # Heyannir (mid July - mid August, " Hay business month") # Tvímánuður (mid August - mid September, "two" or "second month") # Haustmánuður (mid September - mid October, "autumn month") Notes See also |