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York University
Natural Science
NATS 1745
Robin Metcalfe

Chapter 1 Exam Review 1. • It is aligned to the winter solstice. Spiral designs line the walls and cover the boulder, which is at the front of the entrance. Sunlight travels through the passageway, reaching a tomb at the end. Alignment of the tomb likely reflects a belief of rebirth/reincarnation. 2. • At the noon of the solstices and equinoxes, the Sundagger exhibits two beams of sunlight which either bisect or frame the spirals. This makes the Spring equinox, the Summer solstice, the Fall equinox and the Winter solstice. 3. • It is aligned to the Summer solstice sunrise. The Sun rises behind the heel stone. 4. • When it was built, the Summer solstice rose beside the heel stone (due to procession of equinoxes). This suggests that there used to be 2 heel stones which framed the solstice sunrise. 5. • Due to the Earth’s 24 hour eastward spin around it’s polar axis, the Sun moves westward across the sky; it rises in the East, reaches its highest point at noon, then sets in the West. The Earth spins Easterly (from West to East.) 6. • Local midnight, local noon, local sunrise, local sunset. 7. • Northern hemisiphere WINTER SOLSTICE: NE, Southern hemisphere SUMMER SOLSTICE: SE 8. • Solstice is Latin for ‘solar standstill’. The sun itself never stands still but what we are referring to by the stand still is the rising and the setting position. The sun rises at different locations in the sky every day. When it stops shifting south the stoppage of the shifting for the Winter solstice NE and Summer solstice is SE. 9. • Winter Solstice: SE, SW. Summer Solstice: NE, NW. Equinox: E, W. 10. • On the midwinter solstice, the sun rises behind the leftmost tower of the 13 that makes up the newly discovered solar observatory of Chankillo of Peru. During the next 6 months, it rises behind all the others in turn. In the S-hemisphere, the Sun’s daily arc point N- rather than S. 11. • The longest day of the year is June 22 because it is on the Summer Solstice. Only on this day, the Sun rises and sets at its Northernmost position, traversing a long,ndigh arc in the sky. It has the highest noon Sun. The shortest day of the year is December 22 because it is on the Winter Solstice. Only on this day, the Sun rises and sets and its Southernmost position, traversing a short, low arc in the sky. The lowest noon Sun. 12. • The seasonal changes in the Suns daily arc are due to the Earth’s 23.5° tilt from its orbit around the sun. Winter – When a hemisphere is tilted away from the sun, sunlight hits indirectly (at an angle) causing low arcs and less light per area. Summer – When a hemisphere is tilted toward the sun, sunlight hits more directly, causing high arcs and more light. When one hemisphere is tilted toward the Sun, the other is silted away. Therefore, each hemisphere experiences opposite seasons at the same time. 13. • Only within the Tropics ‘of Cancer and Capricorn’so either N or S of (23.5 degrees from the equator) can the Sun be seen directly overhead. They got these names because those are the constellations that can be seen when the Sun is directly overhead. 14. • Within 23.5° of the poles (Arctic andAntarctic Circle) the Summer solstice sun does not set, which causes a polar day – 24 hours of daylight.Also, the Winter solstice sun does not rise, causing a polar night – 24 hours of night. 15. • The Zenith is the point on the sky directly above the observer. The altitude of the zenith is 90 degrees. The altitude of the horizon is 0 degrees. Astar halfway up is 45 degrees. 16. • Altitude and azimuth are relative; they are location dependent and change with the observer’s location. Declination and Right Ascension are absolute; they are NOT location dependent and always stay the same despite the observer’s location. 17. • The star is 10 degrees north from the Celestial Equator (CE). It is 1h from the sun’s position at spring equinox. 18. • If the starts are rotating around our zenith, this mean our zenith is the northern celestial pole so we must be at the north pole (latitude of 90 degrees north). The stars rotate around the N celestial pole. If we walk south, the NCP’s latitude will decrease until we hit the equator; at which point the NCP will be along the horizon at 0 degrees which means the observer is at a latitude of 0 degrees (equator). When you are south of the equator, this point becomes part of the invisible sky below the horizon. 19. • Since Polaris (The North Star) marks the North Celestial Pole, a Northern observer’s latitude equals Polaris’latitude. 20. • Pleiades, which are a group of stars in the sky in that area. Stars, star clusters. The first half started in December, when they saw the Pleiades rising as the sun set. The second half started in May or June, when they Pleiades were first visible in the morning sky. 21. • The Polynesians, who were scattered over 1000 islands in the South Pacific, traversed their islands by canoe using the stars. Chapter 2 Exam Review 1. • For the ancient Chinese, the sky was the mirror of the Earth. By keeping a close eye on the heavens, the Emperor could check what was happening in China.Astrology was the whole reason for watching the sky. They believed that the sky was intimately related to the events on Earth. It was a type of astrology. The ancient Chinese believed that when they saw chaos in the sky, chaos was going to happen on earth -> specifically government. The planets, they understood that the planets were normal. They have a predictable order/cycle whereas comets and supernovae don’t. They are chaotic. When something unusual happened, like comet and supernovae, there was a sign that something chaotic was going to happen. 2. • The Crab Nebula is the debris from a supernova that the Chinese saw explode inAD 1054.At the heat of the twisted remains of the old supernova lies a rapidly spinning relic of the explosion, the Crab Pulsar. For today’s astrophysicists trying to understand the nature of pulsars, the Chinese records provide one vital clue that they can’t find out any other way: the age of the Crab Pulsar. It formed when the core of the supernova collapsed, so the Chinese skywatchers reveal that the pulsar is just over 950 years old – a mere youngster on the cosmic stage. In the center, is this star that is flashing, how do we know its 950 years old? Because pulsar occurred when supernovae was born, and we know that the number of years ago of the supernovae marks the date of the pulsar. Know date of supernovae, know date of pulsar. 3. • 365 steps (shows Mayans were aware of and understood the Sun’s annual cycle.)Annual serpent pattern of light and shade tracks the time of year (eg. On the equinoxes, full serpent ends at Kukulcans head.) 4. • Openings in the observatory dome are aligned to the Northernmost and Southernmost setting positions of the planet Venus (allowed the Maya to measure the duration of Venus’ full path in the sky.) 5. • Durable books containing listings of historical events, including celestial events (eg. The Dresden Codex” contains Mayan dates of the full eclipse cycle and the Venus cycle.) 6. • 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. The Maya, TheAncient Chinese and the Babylonians, however, found their pattern. 7. • Lunation – one complete cycle of the moon phases (29.53 days.) As the moon orbits Earth once a month, Earth sees different portions of its sunlit side, causing the Moons appearance to cycle from completely dark (New Moon) to completely illuminated (Full Moon.) 8. • New moon is when the moon is between the earth and sun, full moon is when the moon is on the other side. First quarter moon is when it is perpendicular (bottom of the moon), the 3 quarter is the opposite. 9. • When the Moon is Waning (from full to new), it’s lit on the left. When the Moon is Waxing (from new to full) it’s lit on the right. 10. • When the moon is in the crescent shape, on the same side of the side, we can also see the sun in the sky. When its in the gibbous shades, we are looking at the side of the sky where its night time. 11. • Occurs when the Moon (New) passes between the Earth and Sun, and casts its shadow on the Earth. 12. • The observer is standing in the umbra the total shadow. They must be standing in the penumbra for a partial solar eclipse, looks like a chunk taken out from the sun. 13. • There are two kinds of shadows, which can be cast on the Earth by the Moon:Atotal eclipse is seen from the parts of Earth in the Moon’s primary shadow (Umbra). Apartial eclipse is seen from the parts of the Earth in the Moon’s secondary shadow (Penumbra) If outside the penumbra, they are seeing a perfectly normal sun. 14. • Occurs when the Moon (Full) passes through the Earth’s shadow. 15. • Penumbral eclipse – When the Moon passes through Earth’s penumbra. Partial eclipse – When a part of the Moon passes through Earth’s umbra. Total eclipse – When the entire Moon passes through Earth’s umbra. Appears red because its light has been so dimmed that only its red light makes it through our atmosphere. 16. • Total solar eclipse is a full moon being taken over Apartial and penumbra look like a bit of the moon is being taken over 17. • Yes the eclipses moon appears the same for all observers that is not the case for the sun it is location dependent. 18. • Its because the moon has a 5 degree tilt The eclipse season Occur approximately twice a year It is because an eclipse season is longer and lasts 31-38 days 19. • Since an eclipse season is greater/longer than 1 lunation, there are 1-2 lunar and 1-2 solar eclipses each season, though only 1 lunar per year and 1 solar per 1.5 years are visible. (Solar eclipse will be seen less, since the observer must be in the Moon’s shadow.) 20. • Bottom of each page containts a series of 177s (number of days in 6 lunations) and 148s (number of days in 5 lunations.)Above each 177 or 148 are the range of Mayan dates expected for that season’s eclipse, meaning that they could predict eclipses with certainty of within a day. The table spans 1 complete eclipse cycle of the Mayan dates, so eclipse warnings could be predicted for eternity. 21. What 2 characteristics of the planet Venus caused the Mayans to identify it as a special kind of star? Why did they worship this planet? • The 2 characteristics of Venus are that it ‘disappears’for 3 monthsand it is the brightest next to the Sun and the Moon. Significant to them because it represented their Supreme God Kukulcan. (Disappeared into forest, never returned, Venus rose brightly in sky above forest where he disappeared.) 22. • The heliacal rise of Venus, when it first rises in the morning sky in the east, marks the direction of sunrise and rebirth. Cosmical rise, when Venus rises at sunset in the west, is associated with evening and death. 23. • It appears as a morning star Dimmer because it is further from the sun Venus’dark side faces the Earth No, it’s an evening star Brighter. Venus is hidden by the sun’s glare. 24. • Each row gives the 4 Mayan dates of the appearances and disappearances in each 584- day Venus cycle. They present Venus’appearances and disappearances. Significance is that they can predict it for eternity. 25. • In ancient Egypt, survival depended on the annual flooding of the Nile River. The sky was therefore studied for the time keeping. 26. • Due to earth’s annual orbit around the sun, our visible window of starts changes each night, so the starts we can see tell us the time of each year. When a star returns to the same position in the sky, earth has completed 1 orbit (exactly 365.25 days have elapsed). 27. • Within the latitudes of Egypt, the heliacal rise of Sirius (the brightest star in the sky) coincides with the Nile’s annual flood. Sirius’heliacal rise was therefore used to mark each year. 28. • The Egyptians tracked time at night using a set of constellations which rise at approximately equal intervals. On average, 12 of these constellations rise at each night, so the Egyptians divided night and day into 12 hours each. 29. • The Alexandrian government of Egypt established a calendar containing 12 30-day (360 days) within 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 season. 239 BC: Ptolemy 3 added another leap day every 4 years: 4yrs x 365.24 days/yr = 4 365- day civic years + 1 days – 11.5 mins. 46 BC: on the advice of the Egyptian astronomer Sosigenes, Julius Ceaser incorporated the 4-year leap-day into the Julian Calendar (a 365-day calendar with 12 months of 28-31 days). 16 C: 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) 30. • Because it is the one that is in sync with the seasons 31. • The motivation was astrology. The Babylonian people ruled by using that. They didn’t have as much rainfall (not the same cycle) as Egypt. They thought the sky would help them predict weather cycles. 32. • Earths daily spin is slowing down, the length of a day is slowly increasing. Nothing we need to worry about because it’s a regular cycle. 33. • Along with their meticulous observations of the sky, Babylonians developed some pretty clever mathematics. Instead of being based on 10, though, their number system hinged around 60. That’s why – to this day, we have 60 minutes in an hour, and 360 (6x60) degrees around a circle. They used a 60-based number system and it is an easily divisible number. 34. • Constellation the sun passes through throughout the year. Not only is the sun limited to those constellations, so are the planets. They are interested what zodiacs planets were in. we can see them because it is the constellation you can see during the day when the sun is out. 35. • Mercury (speedy scribe/ messenger god): named for its fast motion across the sky. Venus (goddess of love/ beauty): named for its brightness. Mars (god of war/ bloodshed): named for its red color. Jupiter (father of the gods): named for its brightness and majestic motion. Saturn (god of old age): named for faintness/ slow motion. 36. • A. Supernova: the explosive death of a massive start (can appear as a temp. star; ‘nova stella’= new star) B. Nova: the re-ignition of a dead star, which has yanked fresh gas (star fuel) from a companion star (can appear as a sudden temp. star) C. Comet: a rocky snowball in orbit around the sun (can appear as a temp. star) 37. • Aplanetary conjunction: when multiple planets line up in the same region of sky (not star-like, but a rare and predictable event with astrological importance). 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. NOT FINISHED (ANCIENT CHINAPART) Chapter 3 Exam Review 1. • The rule was decentralized; there was not one kingdom, which had control over people. Geography was more fragmented (Greece). You don’t all have to work for the same kingdom. Investigate your own things. 2. • He is called the father of science for attempting to find explanations for natural phenomena that didn’t involve the gods. His philosophy gained support when he demonstrated that some acts of nature (eg. Eclipses) are predictable. 3. • He believed that the earth was ‘afloat’in the air. 4. • 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 obeys knowable laws). The taught that all celestial motion is perfectly circular, and that earth is a sphere. 5. • A. Ships gradually disappear in the horizon bottom-first. B. Earth’s shadow on the eclipsed moon is always round. C. When you travel North or South, the constellations rise and set more rapidly than they would if the Earth was flat. 6. • 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. 7. What did Herakleides believe about the Earth? • With no reports from travellers of the ‘central fire’, he removed it, and set Earth spinning daily around its own axis. 8. • He placed Mercury and Venus in orbit around the Sun to explain the sun-centered appearance of their motion and their brightness changes. 9. • Aristarchus 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. His measurements weren’t accurate, but he correctly deducted: the sun is much larger then Earth, and Earth is larger than the moon. This led him to propose a heliocentric model of the universe, with only the moon in orbit around Earth (owing to the moon’s straight night – to – night path around the sky). 10. • Planets display both direct (forward) motion (W to E) and retrograde (backwards) motion (E to W). 11. • From Earth, the speed of the planets look non-constant is what we see. The brightness also looks non-constant. 12. • All celestial bodies are perfect unblemished spheres with constant motions. 13. • Crystal orbs 14. • To explain retrograde motion. 15. • The Earth is at the center. Made of ether quintessence The Earth is fixed at the center of the universe (geocentric). All matters in the terrestrial realm is composed of four elements: earth, water, air and fire. 16. • He used eudoxus’model of the crystal orbs. They are perfect circles. They have constant speed through space. 17. • He said the Earth is fixed and that surrounding our entire universe is one enormous crystal orb that spins once a day, and it explains why the sun rises and sets every day. 18. • Prime
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