Since the solar year 265242 days the civic calendar

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Since the solar year = 265.242 days, the civic calendar gradually crept ahead of the seasons 239 BC: Ptolemy III added another leap day every 4 years: 4 year *365.242 dats/years =4365 day civic year + 1 day – 11.5min 46 BC: an the advice of the Egyptian astronomer sosigenes, Julius Caesar incorporated the 4-year leap-day into the Julian Calendar (a 365-day calendar with 12 months of 28, 30 or 31 days) 16 th C: Pope Gregory XIII fixed the 11.5min error by decreeing : years divisible by 100 ( but not 400) are not leap years ( our modern Gregorian Calendar) The Origin of the 24-hour clock The Egyptians tracked time at night using a set of constellations which rise at approximately equal intervals. On average, 12 of these constellations rise each night, so the Egyptians divided night and day into 12 hours each Babylonian Astronomy (2000-331 BC) The Babylonians tracked the cycles of the sky, which they believed to foretell the future This was the origin of western astrology
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Each night, a record of the sky was entered a tablet, the daily records, combined with a book of interpretations, were used to predict the celestial events (and their oments) for the next year. The Babylonians divided the stars into groups (constellations) and passed on ther descriptions to the Ancient Greeks, from whom today’s constellation names originated. (diagram: CH 2-26) The constellation around the ecliptic held a special/significances, as the planets move along this strip of sky. The Ancient Greeks named these the zodac constellations (Greek “ circle of animals” ) Tycho Brahe (1546-1601) - Found errors in the predictions of both Ptolemaic and Copernican models. - Made the most accurate pre-telescopic measurements of planetary coordinates - His goal: to determine the true model of planetary motion. - Tycho observed that the coordinates of the 1572 supernovae (“Tycho’s Star”) remained fixed relative to other stars, which meant: It occurred in the orb of stars The orb of stars is not unchanging - The king of Denmark granted Tycho an island, where he built two elaborate observatories in order to conduct his high-precision cataloguing of the celestial bodies. - Even with his high-precision instruments, Tycho could not detect stellar parallax. - The smallest angular shift Tycho could measure was 1 degree/60 th , which meant: If Earth moves, a<1 degree/60 th for all stars From the parallax equation, d> 7000 AU for all stars (i.e. 700x Saturn’s distance) - Since 7000 AU seemed inconceivably large, Tycho concluded that Earth is fixed. - This led him to the Tychonic System, which is nearly geometrically equivalent to the Copernican and therefore just as accurate. - Pic next page…
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- Animation: The Copernican System - The initial obstacle to the acceptance of this system: the intersection of the “crystal orbs” – how could Mars pass through the Sun’s orb without shattering it?
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