Year and Subdivisions A. AD, BC, CE, and BCE · AD: Anno Domini: After the birth of Christ: BC: Before Christ; CE: Common or Christian Era; and BCE: Before Common or Christian Era (to avoid Christ in terms of his birth) · Adoption of birth of Christ as epoch (initial, start) 6th century scholar Dionysius Exiguus compiled table of values for Easter. · Dionysius chose to number the years since the birth of Christ, rather than honor the persecutor Diocletian (284-305) · Dionysius (wrongly) fixed Jesus' birth with respect to Diocletian's reign in such a manner that it falls on 25 December 753 AUC (ab urbe condita, i.e. since the founding of Rome), thus making the current era start with C.E. 1 on 1 January 754 AUC. · There is no year zero, thus 1 BC to 1 AD; also Jesus was really probably born 7BCE (?) · Easter: celebration of death and resurrection in C.E. 30; first Sunday after the first full moon after vernal equinox. · Astronomers: Instead of 1 B.C.E. they use 0, instead of 2 B.C.E. they use -1, instead of 3 B.C.E. they use -2, etc. B. “Our Year”: based on the earth's motion around sun. The time from one fixed point to the next is called a tropical year (mean interval between vernal equinoxes), length is currently 365.242190 days, but it varies. Around 1900 its length was 365.242196 days, and around 2100 it will be 365.242184 days · Solar Calendar: based on tropical year, sidereal · Lunar Calendar: synodic month: from one new moon to the next, varies: in 1900: 29.5305886 days, 2100 it will be 29.5305891 days, synodic · Lunisolar Calendar: tries to have tropical year coincide with lunar months; length of the tropical year is not a multiple of the length of the synodic month. Means addition of months and/or days, 19 tropical years is 234.997 synodic months · Millennium: first millennium started in 1 AD – 1000AD, second is 1001 – 2000 millennium, third is 2001-3000 · Leap year: 970 leap years for every 4000 years by Gregorian calendar C. Julian Period · The Julian period (and the Julian day number) must not be confused with the Julian calendar (7980 years) · Joseph Justus Scaliger (1540-1609): interested in assigning every year a positive value without worrying about BCE/CE; invented what is today known as the Julian Period. o Starts on 1 January 4713 B.C.E. (Julian calendar) and lasts for 7980 years. C.E. 2000 is thus year 6713 in the Julian period. After 7980 years the number starts from 1 again. o In 4713 B.C.E. the Indiction, the Golden Number, and the Solar Number were all 1. The next times this happens is 15 x 19 x 28 = 7980 years later, in C.E. 3268 · Indiction Number: [(Y+2) mod15] + 1 (first used by Constantine the Great on 1 September 312AD) used in the middle ages to specify the position of a year in a 15 year taxation cycle by emperor, ceased to be used in 1806. Had nothing to do with astronomy · Golden Number: [Y mod 19 + 1 = 5] · Solar Number: [(Y + 8) mod 28 + 1 = 20] D. Month · Length and how many days relate to type of calendar and civilization · Origins of current Gregorian months: (Mostly derived from Latin) o January (Januarius): god Janus; February (Februarius): Februa (purification festival); March (Martius): god Mars; April (Aprilis) after Aphrodite or latin word aperire (to open), May (Maius): goddess Maia; June (Junius): goddess Juno; July (Julius): after Julius Caesar in 44 BCE; prior name was Quintilius from quintus meaning 5 in old Roman Calendar, August (Augustus) after emperor Augustus in 8 BCE, prior name was Sextilis from sextus meaning 6 in old Roman Calendar; September: septum (7th month in old Roman calendar), October: octo (8 in old Roman calendar ). November: Novem (9th in old roman calendar); December: decem (10th in old Roman calendar) · Week/month not based on each other: lunar month is not a 28 day cycle and 29.5306 days cannot be neatly subdivided into weekly blocks of complete days, 12 months is about 11 days shorter than tropical year) E. Week: Jewish cosmology vs. ancient astrology · Jewish: seven days of creation; Hebrew word for week shavu’a interchangeable with Sabbath shabbath which came from verb sh-b-th which means to cease from labor; practice of working 6 days and resting on seventh “practiced by God when creating universe” but probably most likely a product of Exile period in Jewish history (586 BC) · Need for continuous week for “settled” life and social organization continuity could not be interrupted by such natural phenomena as the lunar cycle; the break from relying of a multiple of a day as opposed to a approximation of a lunar month was a huge step; the first to do so was ancient Egyptians; · Seven planets of ancient astronomy: Saturn, Sun, Moon, Mars, Mercury, Jupiter, and Venus; moved regularly across sky o Greek verb “planasthai” to wander o Original Babylonian/Mesopotamia reason to develop astronomy tables was to design horoscopes, but there were no “day of Moon” o Astronomical week came after Alexander the Great’s conquest of western Asia (2nd century BC) o Astronomical practice to arrange in order: Saturn-Jupiter-Mars-Sun-Venus-Mercury-Moon, mathematical practice to subdivide daily cycle into 24 hours integrated, order due to geocentric distances (Saturn and Moon being farthest and nearest, incorrect), sequence of planetary days consists on planetary leaps (skipping two planets each time) · Spread of seven day week: growing popularity of astrology, church integrated Jewish and astrological weeks together o Sunday first day of week, “Lord’s day”, Early Christians were Jewish and observed both Sunday and Saturday until identity as both Christian and Jew was difficult to maintain, at this times social contrasts within calendars became established, however, chose to keep seven day week even though could have used Roman’s Eight day week o Islam spread seven day cycle to east coast of Africa, Sudan, Central Asia, North and West Africa, Mohammed’s choice of Friday for public worship may have been to separate from Jewish Saturday and Christian Sunday · Ancient Greek split month into 3-10 day weeks, Romans had market week of 8 days with 1 day of rest and celebration, French: 10 days in a week, Maya have 13 and 20 day weeks · USSR: tried a five day week (1929) and a six day week (1932), restored to seven day by 1940 F. Day · Subdivision of 24 hours was Egyptian mathematical practice · First clocks did not have minute hands, minute was not important until Industrial revolution · Daylight Saving (NOT savings) Time o Save energy, enjoy light later on summer evenings o USA 1925(most): begins at 2 am on the first Sunday in April, ends at 2 am on last Sunday in October change from 1:59 AM to 3:00 AM, EU (1996) begins at 1am according the Universal Time (Greenwich Mean Time) last Sunday in March and ends last Sunday in October, first conceived by Benjamin Franklin in 1784, seriously considered in 1907 by William Willett by advancing clocks 20 minutes four Sunday in April and turning them back by 20 minutes four Sundays in October to take advantage of the daylight, he lobbied for a year and died before it changed Major Calendars A. Early Greek (between 700 BC - 300 AD) · Astronomy: did not include physics, only sought to describe the heavens with mathematics, · Many Calendars: the day was first natural period of time, also periodic phases of the moon, but approximate length of year was necessary for agriculture o 12 months of 30 days, moon rapidly gets out of phase o By 600 BC: a year was 6 full months of 30 days and 6 empty months of 29 days o Solon (600 BC) based on two year cycle 13 months of 30 days and 12 months of 29 days (378 days/2 = 369 days) · Pythagoreans (500 BC): earth was a sphere, orbit of moon inclined to equator of earth, venues as evening star was same as morning star o Oenopides (450 BC) discovered ecliptic made a 24 degree angle with equator (refined by Eratosthenes 250 BC); 59 year calendar cycle with 730 months o Philolaus: 59 year cycle of 729 months: 729 = 27squared, 27 was number for moon and 9cubed since 9 was number for moon · Meton (432 BC) calendar based on 19 year cycle (similar to one we will talk about from Babylonian), also made observations of solstices to determine length of tropical year · Spherical geomtry (Autoycus) was next major development to aid in astronomy (330 BC) · Euclid worked on and wrote Phaenomena: elementary astronomy and times when stars in certain positions rise and set · 260 BC Alexandria: accuracy increases with acitve measuring, equatorial and ecliptic systems originate · Aristarchus (310BC – 230BC): ratio of distances to the moon and sun showed sun much further away , sun much larger than earth which may have led to the heliocentric theory (found little favor with Greeks) · Archimedes (287 BC-212 BC): designed planetarium. Measured diameter of sun · Eratosthenes (276 BC-194 BC): size of earth , accurately measured ecliptic, improved calendar B. Egyptian · Because of difficulties to align solar calendar and lunar calendar – Egyptians used three · First strictly lunar calendar, but this failed to predict flooding of Nile accurately: regulated lunar calendar by means of the guidance of a sidereal calendar. · ‘Discovered’ Sirius “Dog Star” whose “rising” corresponded to true solar year, only 12 minutes shorter, brightest “fixed” star · 8th century B.C.E., the Egyptian pharaoh’s primary advisor, the Vizier was to report when Sirius was absent from sky for approximately two weeks.