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NATS 1745: chapters 1-7 textbook/video notes

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York University
Natural Science
NATS 1745
Robin Metcalfe

NATS EXAM CHAPTERS 1-7 Chapter 1 Textbook Notes  Fajada Butte, ceremonial astronomical centre for ancient inhabitants of western north america  Winter and summer solstices and at equinoxes, sunlight shines through in bright sun daggers onto spiral patterns carved on the rock behind  Chaco Canyon where Fajada Butte is located reveals a number of alignments that relate to the sun and the sky  Ceremonial life in these ancient villages revolved around their observation of the sun and the moon, provided a calendar for farmers etc  Around 1000 AD this canyon was the centre of astronomy  Great Houses also built around astronomy o Solstice: occurs twice each year as the Sun reaches its highest or lowest excursion relative to the celestial equator on the celestial sphere. As a result, on the day of the solstice, the Sun appears to have reached its highest or lowest annual altitude in the sky above the horizon at local solar noon. Summer – highest position in sky. Winter- lowest position and sky o Equinox: Occurs twice a year when the plane of the Earth's equator passes the centre of the Sun. At this time the tilt of the Earth's axis is inclined neither away from nor towards the Sun. Days of equal day and night.  Set of rocks in one valley that track equinoxes  Stonehenge in England, monumental shrine to the sun  Early astronomers made precision observations of the sun and the moon from the stonhenge, using four markers they could calculate eclipses of the sun and the moon  Some deny its significance and that it could be used to predict eclipses  Nebra sky disk with astronomical symbols also found, golden arcs that stretch 82 degrees around the circumference, the extent that the sun moves around the horizon  Thirteen towers of Chankillo, at winter solstice the sun rises behind the leftmost tower, the progress of the months is marked by the sun rising behind each of the towers until it rises behind the rightmost stone  Polynesian islands had star compass that divided the horizon in 32 different directions corresponding to bright stars  Used the sky to navigate the ocean Chapter 2 Textbook Notes  Ancient Chinese oracle bones, the start of precision astronomy (37)  For ancient Chinese the sky was a mirror of the earth (37)  Ancient observatory of Beijing still stands to this day  Main influence was astrology, they would interpret things such as comets (41)  Stars represented famous charioteer (42)  Crab pulsar formed when when the core of the supernova collapsed, just over 950 years old (42)  Halley’s comet (42)  Chinese concerned with eclipses (42)  Used moon to divide sky into 28 wedge shaped lunar mansions (42)  Planets were not so important with exception of Jupiter because it marked out years and eventually used for 12 animals of Chinese astrology (42)  Believed that sun moon and stars floated freely (44)  Dresden Codex- reveals that Mayans were astronomers (44)  However, their motivation was to determine what was going to happen to kings through astronomy (44)  Governor’s House at Uxmal lines up with distant pyramid marking the southernmost point where venus rises on the horizon (44)  Dresden Codex described in detail how Venus moved across the sky (44)  Only 4 remaining Mayan codices, so Venus may not be as important as these codices lead us to believe (46)  Mayans ran 3 separate calendars at once, one repeated every 260 days, one every 360 days and one 365 days (46)  Chichen Itza, pyramid of 9 platforms each diminishing in size (46)  On equinoxes, the setting sun casts a shadow on platform edges forming a giant snake (46)  Pyramids at Giza in Egypt are aligned to 4 points of the compass  Great Pyramid of Khufu, oldest of the ancient seven wonders of the world (47)  Lined up north-south with a precision that astronomers didn’t achieve again until the time of Tycho Brahe 4000 years later (47)  Egyptians had a pattern of stars recorded in tomb sealings, yet never put the stars in those illustrations (47)  Sirius underpinned the whole of Egyptian life, helped them know when Nile would flood (47)  Picked 35 stars that would rise before the sun at 10 day intervals – the decans (48)  Used for timekeeping at night (48)  24 hour day (48)  Also observed the stars in reference to their gods (48)  Babylonians developed mathematical astronomy (48)  Record of eclipses, earth slowing down and it’s not just the moon’s gravity brake changing the way the earth spins (50)  As ice sheets melted, earth’s surface area bounces back (52)  Babylonians focused on motions of planets (52)  Among the oldest constellations may be the Plough or Big dipper (53)  Origins of constellations (53)  Mesopotamia- record of our constellations of the zodiac (53)  Zodiac provided path followed by the moon and planets (53)  Babylonian number system based around 60  They would record what would be happening in the sky in the upcoming months (55)  Wise men from st. matthew’s gospel were probably astrologers from Mesopotamia 55)  1604, Kepler witnessed supernova (55)  Around 7-6 BC similar grouping of planets, may have produced what was believed to be the star of Bethlehem Chapter 2 Video Notes  The maya tracked celestial cycles in order to worship Mayan gods associated with celestial bodies  Astronomy in Europe at this time was far above what the Maya had achieved, but having been isolated their achievements were all their own  Identified long term complex cycles  Pyramid of Kukulcan, 365 steps – shows Mayans were aware of sun’s annual cycle, annual sepent-pattern of light and shade tracks the time of year (ex on equinoxes full serpent ends at Kulkulcan’s head  Evidence that pyramid was used as a calendar, shadow pattern was used to identify days  El Caracol – observatory, openings in the observatory dome is aligned to Northernmost and southernmost postitions of the planet Venus while setting (allowed the Maya to measure the duration of Venus’ full path in the sky)  Used Venus to time their worship for Kulkulcan  Maya had to track Venus daily for over 3 years in order to accurately track the cycle of Venus  Mayan bark books – containing listing of historical events, including celestial events like the Dresden Codex, contains Mayan dates of full eclipse and the venus cycle  Over 400 months worth of eclipse predictions th  Created by Maya in thirteenth century, reproduction of findings of 8 century  December 21 2012- this is the last date of one calendar cycle, not the last date of all time  Mayan number symbols visually represent their quantity, making them efficient for addition and subtraction of large numbers, allowed them to easily record the number of days between celestial events and to recognize their long term patterns  Eclipses were believed by many civilizations to be heralds of bad times, due to the damaged appearance of the sun or moon  Their long-term complex cycle led many to believe that eclipses are random, however the Maya found their pattern  Appearance of sun and moon being consumed, unsettling for early civilizations  18 years for cycle of eclipses to repeat itself  Lunation: one complete cycle of moon phases (~29.53 days)  As the moon orbits earth once a month, earth sees different portions of its sunlit side, causing the moon’s appearance to cycle from completely dark (New) to completely illuminated (Full)  The larger visible portion of the moon’s sunlit side, the more nighttime hours the moon is visible (full moon can only be seen at night)  We can only see moon when it is above our horizon  Solar eclipse: when the moon (new) passes between earth and the sun and casts its shadow on earth  Umbra – darkest part of the moon’s shadow  Total eclipse is seen from the parts of Earth in the Moon’s primary shadow (umbra)  A partial eclipse is seen from the parts of Earth in the Moon’s secondary shadow (penumbra)  Most total eclipses aren’t seen at all, umbra sometimes passes only over the ocean  A lunar eclipse occurs when the moon (full) passes through earth’s shadow  Penumbral eclipse: when the moon passes through earth’s penumbra  Partial eclipse: when a part of Moon passes through Earth’s umbra  Total eclipse: when entire moon passes through earth’s umbra  Total eclipsed moon appears red because its light has been dimmed so only its red light makes it through our atmosphere  The appearance of the eclipsed sun is location-dependent, while the eclipsed moon appears the same for all observers  Eclipses do not occur every new and full moon:  Due to the 5 degree tilt of the moon’s orbit, earth moon and sun are usually not in the same plane, therefore no eclipse  Eclipse seasons (when moon earth and sun are coplanar) only occur 2-3 times per year and last 31-38 days  Since eclipse season> 1 lunation, there are 1-2 lunar and 1-2 solar eclipses each season, though only 1 lunar/yr and 1 solar/1.5 yrs are seen (solar seen less since observer must be in moon’s shadow)  Moon must be new for solar eclipse, full for lunar eclipse  The Mayan eclipse records include 8 pages of the Dresden Codex which contain symbolic illustrations of eclipses  Bottom of pages contain a series of 177s and 148s (# of days between eclipse seasons  Above each 177 or 148 are the range of Mayan dates expected for that season’s eclipse  Eclipse warnings could be predicted for eternity  Easter Sunday is defined as the first Sunday after the first full moon after the spring equinox  Next to the sun and moon, Venus is the brightest object in the sky  In a given night, Venus moves with the stars due to Earth’s spin. But from night to night, Venus changes its position relative to the stars revealing itself as a planet (Greek for wanderer)  Every 584 days, Venus traverses a half-loop around the rising sun, then disappears  When it reappears, it makes a half loop around the setting sun then disappears again  The Mayan venus records, 6 pages of Dresden Codex contain illustrations of Mayan war hero kulkulcan who was deified and linked with the planet venus  On each page, bottom 4 numbers are the number of days between the 2 appearances and 2 disappearances of Venus  Each row gives the 4 Mayan dates of the appearances and disappearances in the 584 day Venus cycle  In ancient Egypt, survival depended on the annual flooding of the Nile river  The sky was therefore studied for time keeping to ensure crops were planted before the floods  Due to earth’s annual orbit around the sun, our visible window of stars changes each night, so the stars we see can tell us the time of year  When a star returns to the same position in the sky, earth has completed 1 orbit (exactly 365.35 days have elapsed  Within the latitudes of Egypt, the heliacal rise of Sirius (brightest star in the sky) coincides with the Nile’s annual flood. Sirius’ heliacal rise was therefore used to mark each new year  Origin of the 24 hour day: 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  Origin of the leap year:  Alexandrian gov’t of Egypt established a calendar containing 12 30-day months (360 days) with 5 leap days to stay synchronized with the 365 day seasonal cycle  Since the solar year= 365.242 days, the civic calendar gradually fell behind the seasons  239 BC, Ptolemy III added another leap day every 4 years: 4 yrs x 365.24 days/yr = 4 365 day civic yrs + 1 day – 11.5 min  46 BC, on advice of Egyptian astronomer Sosigenes, Julius Caesar incorporated the 4 year leap day into the Julian calendar, first form of our modern calendar th  16 Century: Pope Gregory XIII fixed the 11.5 minute error by decreeing: years divisible by 100 (but not 400) are not leap years (our modern Gregorian Calendar)  The Babylonians tracked the celestial cycles because they believed that the sky foretold the future, this was the origin of western astrology  Each night, a record of the sky was entered on a tablet. The daily records, combined with a book of interpretations were used to predict the celestial events (and their omens) for the next year  Like the Maya, they used their records to predict the future sky  Each night, a record of the sky was entered on a tablet, these records were used to predict the celestial events (and their omens) for next year  Babylonians numbers: a base 60 system, consisting of symbols for 1-60 multiplied by a power of 60, because 60 has many factors (a convenient base for division  They therefore used units that are multiples of 60: 60 min= 1 hour, 60 sec= 1 min, 360 degrees = 1 circle  The zodiac: Babylonians divided the stars into groups (constellations) and passed on their descriptions to the Ancient Greeks from whom today’s constellation names originated  Constellations on the ecliptic (the zodiac constellations; Greek for “circle of animals”) held a special importance as the sun, moon and planets move along this strip of sky  Your zodiac sign is the sun’s constellation in the month you were born  Due to the precession of the equinoxes, the sun’s constellations have changed since the zodiac signs were assigned 2000 years ago  The Babylonians named the 5 visible planets after the gods they best described. The ancient greeks adopted this practice which led to the greek, then latin planet names we use today (Jupiter, Saturn, Mars, Venus, Mercury)  The star of Bethlehem- what was it?  Supernova- the explosive death of a massive star (can appear as a temporary star “nova stella”  Nova- the re-ignition of a dead star which has yanked fresh gas (star fuel) from a companion star (can appear as a sudden, temporary star)  Comet- a rocky snowball in orbit around the sun (can appear as a temporary star)  Comet convinced Rome that Julius Ceasar had become a god  A supernova, nova or comet is unlikely, as no other civilization recorded a sighting around 0 BC  The only other scientific possibility: a planetary conjunction, when multiple planets line up in the same region of sky (not star-like, but a rare and predictable event with astrological importance to the Babylonians) – doesn’t really match the description of the star of Bethlehem  In Dec of 7 BC a Jupiter-saturn conjunction occurred in the Pisces constellation (the ancient sign of the Jews) which occurs every ~800 years Chapter 3 Textbook Notes  Antikythera Mechanism, first computer, clockwork mechanism which was used to predict positions of suns and moon in the sky along with eclipses (58)  Circular gears reflect greek obsession with circles and circular paths (59)  Ancient Greeks invented science, figured objects in sky can move without supernatural force (59)  Thales was first scientist (59)  First to suggest that natural forces responsible for events in the world (60)  Made first accurate prediction of eclipse of the sun May 28 585 BC (60)  Pythagros, theory of harmony in heavens (63)  Pythagros realized earth was not flat (64)  Used moon’s shadow to figure this out, always curved (64)  From 500 BC all educated people knew earth was round (65)  Eudoxus, earth surrounded by mathematical spheres (66)  Aristotle – earth water air and fire, everything is perfect, quintessence (66)  Aristarchus applied math to sun and moon (67)  Deduced the moon is half the diameter of our world (it’s really a quarter) (68)  Worked out how much further the sun lies from us than the moon, answer was 19 (68)  Measurements actually underestimated size of sun (68)  Antikythera Mechanism heading toward Rome from Aegean Sea (71)  Hipparchus measured length of year to amazing precision (71)  Hipparchus precession of equinoxes (72)  Precession of equinoxes, constellations change with time (72)  Antikythera Mechanism, sun’s movements, moon’s movements (72)  Seems to be developed based on Hipparchus’ methods (72)  Erasthothenes worked out circumference of the globe (74)  Apollonius – epicycle model (75)  Also used ellipses, moon and planets actually do travel in ellipses (75)  Ptolemy drew together all of Greeks knowledge in Mathematike Syntaxis, Almagest(75)  Lists stars and constellation, everything revolves around earth (75) - Chapter 3 Video Notes - Fragmented geography and rule of Ancient Greece allowed for an intellectual freedom that led to a revolution in scientific thought - Established first institutions for thinking and education - More intellectual freedom, allowed them to take astronomy to a new level - The popularity of Plato and Aristotle led to nearly 2000 years of widespread belief in the geocentric model, even though the heliocentric model was taught in their time - Heliocentrism - celestial bodies revolve around sun - Geocentrism- celestial bodies revolve around earth - Both theories developed from followers of Pythagorus - By around 100 BC the believe of geocentrism prevailed over the truth o Thales (c 624-546 BC)  Considered father of science for attempting to find explanations for phenomena that didn’t involve the gods  Saw that other cultures had different mythological explanations for phenomena  Ex. Earthquake, Greeks believed caused by Poseidon, in Ancient Egypt they believed it was the laughter of the Earth God  He gained support when he demonstrated that some acts of nature (eclipses) are predictable  Anaximander (c. 610-546 BC)  Set the earth “afloat” in air st  Developed the 1 moving model of the universe in which the motion of the celestial bodies is explained by placing them on spinning wheels around earth  Pythagoras (c. 570-495 BC)  According to legend when he discovered that musical pitch is determined by the length of the instrument, he realized the Universe is a cosmos (a harmonious system that obeyed knowable laws)  He taught that all celestial motion is perfectly circular and that Earth is a sphere  Followers believed that to understand Science is to understand the gods  Philolaus (c. 470-385 BC)  Set the earth in motion by allowing earth to rotate once per day around a central fire, the daily motion of the celestial bodies was explained  Herakleides (c. 375-310 BC)  With no reports from travellers of the “central fire” he removed it and set Earth spinning daily around its own axis  He placed Mercury and Venus in orbit around the Sun to explain the Sun centered appearance of their motion and their brightness changes  Aristarchus (c. 310-230 BC)  Used Earth’s shadow on the eclipsed moon to measure the moon’s size relative to Earth’s  Used the angle in the sky between the sun and quarter Moon to measure the sun’s distance and size relative to the moon’s  Measurements weren’t accurate but he correctly deduced that the sun is much larger than earth and earth is larger than the moon  Proposed a heliocentric model of the universe, largely ignored however first person to propose that earth moves through space around the sun Philosophers who lead us away from the right theory:  Plato (c 428-348)  Began an intellectual tradition in which theories of nature were accepted on faith as opposed to proven by observations  Taught that all celestial bodies are perfect spheres with constant circular motion (CCM)  The goal of the philosophers after Plato was to explain how the planets’ paths in the sky can be explained by CCM  Eudoxus (c. 410-355 BC)  Attempted to explain planetary motion by placing the planets on systems of invisible nested spheres “crystal orbs” each spinning with CCM around earth  Aristotle (384-322 BC)  Unlike Plato he taught that theories must match observation, but his neglect of quantitative analysis led him to the wrong conclusions  Apollonius (c. 250-220 BC)  Upgrade Eudoxan planetary model to epicycle model, accepted for over 1500 years  Epicycle model has CCM and explains retrograde motion, non-constant brightness and non constant apparent speeds  Eratosthenes (c. 276- 195 BC)  Estimated earth’s circumference by measuring the angle spanned by the shadow cast by a stick  Hipparchus (c. 190-120 BC)  Compiled the 1 comprehensive star catalogue (~1000 stars) in the western world  Perfected the geocentric epicycle model for the Sun and moon’s motion  Claudius Ptolemy (c. 150 AD)  Author of Mathematical Treatise, aka the Almagest (Arabic: The Great Treatise) the definitive astronomy textbook for nearly 1500 years  Created the Ptolemaic model (a modified version of the geocentric epicycle model which matched the observed motion of the planets with greater accuracy)  Evidence that Earth is a sphere o Ships disappear on the horizon bottom first o Earth’s shadow on the eclipsed moon is always round o When you travel North or South the constellations rise and set more rapidly than they would if Earth was flat  Features of apparent planetary motion (ie the motion of planets we see across the sky) o Planets display both direct (forward) motion (W to E) and retrograde (backward) motion (E to W) o A planet’s apparent speed is not constant (planets appear to slow down and speed up across the sky o At least as far back as the Babylonians this was observed o A planet appears to brighten and dim as it moves across the sky  Aristotelian model o Earth is fixed at the centre of the Universe (geocentric) o If earth spins the arrow must land behind the archer, It doesn’t therefore Earth is fixed o The Universe is divided into the terrestrial realm (Earth) and the celestial realm (the heavens) where different laws of nature apply o Everything in the terrestrial realm is composed of four elements: earth water air and fire o All bodies in the celestial realm are perfect spheres and composed of a pure and imperishable substance called “quintessence” (5th element) or ether (pure air) o Planetary motion follows the Eudoxam model, planets were carried around Earth by invisible spherical orbs with CCM (the daily motion of which is driven by a single outer orb) o “Whatever is moved must be moved by another” the motion of the orbs is supplied by the motionless Prime Mover (a spiritual, godlike entity residing in the outermost orb) o He believed comets were atmospheric phenomena because they don’t appear eternal, therefore they can’t be celestial bodies o Only eternal phenomena could occur there  Precession of the equinoxes o Hipparchus discovered that the sun’s coordinates on a given date are shifting backwards ~1/100 degree per year o Precession causes all star coordinates to shift 1/100 degree east per year, as a result, by 2200 Polaris will no longer mark the North Celestial Pole  Hipparchus’ lost star catalogue o In 2005 a pictorial record of a star catalogue was found on the Farnese Atlas, a 7 foot statue in Naples, Italy o The star coordinates on the statue are precessed ~2100 years from today. This dates the coordinates to Hipparchus’ time, suggesting that the statue was created from his lost catalogue  Features of the Ptolemaic model o the addition
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