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NATS1745 Chapters 1-6 Exam Review.docx

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York University
Natural Science
NATS 1745
Robin Metcalfe

NATS1745 6.0 History of Astronomy, Fall/Winter 2011 Chapter 1 Exam Review ---------- 1. What celestial event is Newgrange aligned to? Describe what happens at Newgrange on this day.  Newgrange’s roof box is aligned to the winter solstice sunrise.  A beam of sunlight hits the roof-box and illuminates the floor, which will eventually illuminate the main chamber.  As sun rises, a light of beam through roof-box 2. Describe what happens to the Sundagger on the solstices and equinoxes.  At the winter and summer solstice, and rise also at the equinoxes, sunlight shines between three giant rocks at the summit of Fajada Butte, throwing bright “sundaggers” onto an intricate set of spiral patterns carved on the rock behind 3. What celestial event is Stonehenge aligned to? Describe what happens at Stonehenge on this day.  Stonehenge is most likely an observatory for following the sun through the seasons. It is a monumental shrine to the sun. Stonehenge’s heel stone is aligned to the summer solstice sunrise. The sun rises just over the heel stone position of the monument on the summer solstice. 4. Why do archeoastronomers suspect that Stonehenge's Heel Stone had a missing partner stone?  The sun used to hit right next to the Heel Stone and that didn’t make sense  Also it was the only stone that was by itself when all other stones in the Stonehenge were in pairs 5. What causes the Sun to rise and set every day?  Due to Earth’s 24 hour eastward spin around its 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. 6. What is the local time for an observer who is directly facing the opposite side of the sky from Sun?  Local Midnight. What is the local time when the Sun is at its highest point in the sky?  Local Noon. What is the local time when the Sun is seen on the Eastern horizon?  Local Sunrise What is the local time when the Sun is seen on the Western horizon?  Local Sunset. 7. What is the azimuth of the noon Sun in the northern hemisphere? How about the southern hemisphere?  Northern Hemisphere its due south.  Southern Hemisphere its due north.  *The reason being is because the sun's daily arc in the Northern Hemisphere is shifted towards the south. The noon sun means that the sun is at its highest point in the sky and it also means our location is directly facing the sun's direction. That's why its due south. "Due" meaning exact.  Apply that same concept to the Southern Hemisphere. The sun's daily arc is shifted towards the North. Once again, the noon sun is at its highest point in the sky and it also means the southern hemisphere's location is directly facing the sun's direction. That explain's due north for them 8. What does the word "solstice" mean? How does it describe what happens to the Sun's rising and setting positions on the solstices?  The word means solar stand still  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 location on the sky everyday  When it stops shifting south the stoppage of the shifting 9. What is the azimuth of sunrise and sunset on the Northern winter solstice? How about the Northern summer solstice? How about the equinoxes?  for the winter solstice, NE and summer solstice, its SE  winter solstice: SE, SW. summer solstice: NE, NW. equinox: E, W 10. Describe how the Thirteen Towers of Chankillo, Peru were used to track the time of year. Given that this site is in the southern hemisphere, what is the approximate azimuth (NE, SE, NW, SW) of the winter solstice marker? How about the summer solstice marker?  On the midwinter solstice, the Sun rises behind the leftmost tower of the 13 that makes up the newly discovered solar observatory of Chankillo in 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.  Remember, dealing with South, which means Winter Solstice Sun is rising NE and Sun setting NW. one of them will be t NE . Sunrise -> points NE. Sunset -> points NW  SE, and SW marked by furthest tower. 11. Which day is the longest day of the year, and why? Which day is the shortest day of the year, and why? What are the lengths of daytime and nighttime on the equinoxes?  Longest day of the year is the Summer Solstice  It's because the sun travels its highest, longest arc which means it’ll be at its highest point in the sky and it'll spend the most amount of time above its horizon compared to other daily arcs that it travels throughout the year  Shortest day of the year is the Winter Solstice  the equinoxes : equal day and night  A. Summer Solstice (June 22): Sun rises and sets at its northernmost position, traversing a long high arc (longest day, highest noon sun) b. Winter solstice (December 22): Sun rises and sets at its southernmost position, traversing a short, low arc in the sky (shortest day of the year and lowest noon sun). c. Fall and Spring Equinox (Sept 23) (fall equinox) and (spring equinox) March 21): Sun rises due E and sets due W, spending equal time above and below the horizon (equal day and night) 12. What causes the seasons? Describe the orientation of the Earth relative to the Sun during Northern summer. What season does the Southern hemisphere experience at this time, and why?  The seasons are caused by the tilt of the Earth’s rotational axis away or toward the sun, as it travels through its year- long path around the sun.  Earth is oriented more toward the sun  winter ?, opposite end, thus less sun? 13. Within what latitudes can an observer see the Sun directly overhead? How did these latitudes get their names?  Only within the tropic of cancer and capricon  Tropic Cancer because if you stay at this latitude, on the day of June solstice, and noon, the sun is in the cancer constellation when it hits the Zenith  And tropic of capricorn, and the definition is similar -> if you stand there when sun hits top of sky in december solstice, noon sun is in capricorn constellation. 14. What are polar nights and polar days? Within what latitudes do these occur?  Polar nights -> 24 hours of darkens inside the polar circles  Polar days - the midnight sun  Polar days and Polar nights occur within 23.5 degrees from the poles in both the artic and antartic circles. 15. Where is the zenith? What is its altitude? What is the altitude of the horizon? What is the altitude of a star that is halfway up the sky?  It is a point in the sky that is directly above you  The altitude of the zenith 90 degrees  The altitude of the horizon is zero  And a star half way up is 45 degrees 16. Does a star’s altitude and azimuth depend on the observer’s location? How about right ascension and declination?  Altitude depends on horizon so the altitude and azimuth does depend on observer’s location  No the ascension and declination does not depend on a person’s location they are absolute co- ordinates 17. If a star has a declination of 10 degrees north, what is the star 10 degrees north from? If a star has a right ascension of 1h, what is the star 1h from?  Matter of remembering definition of declination (What is the definition of declination)  Right ascension is just one hour away from the line it is one hour away from the right ascension line that marks the summer equinox  the celestial equator. the line of zero right ascension, which is marked by the Sun's position on the Spring equinox 18. Where are we on Earth if we see the Northern constellations rotating around our zenith? What is the name of the point that these stars rotate around? What happens to this point if we walk south? Where is this point seen when we’re at the equator? Where is this point when we walk south of the equator?  We are at the north pole exactly  The north celestial pole  It is going to get lower and lower in the sky  It is going to be pointing north  We are not going to be able to see it anymore 19. If an observer sees Polaris at an altitude of 60 degrees, what is the observer’s latitude?  Latitude is equal to the altitude of the polaris 20. What celestial object did the Polynesians use as the basis of their calendar? What does this object consist of? How did the Polynesians use this object to identify the 1st half and 2nd half of their calendar year? In ancient times, how was this object used in the Andes to determine when to plant?  Pleides which are a group of stars in the sky in that area  Stars. Star Cluster  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 the Pleiades were first visible in the morning sky  It had to do whether it was dim or not. If the Seven Sisters were clear and bright, they would plant. If it was dim and hazy they would delay planting. Cloud Cover -> Agricultural. 21. What did the Polynesian navigators memorize in order to steer their canoes while at sea?  What they memorized was the rising and setting stars  They memorized a star compass. It divided the horizon up into 32 different directions, corresponding to the rising or setting of individual bright stars and the all- important Pleiades. Basically, they relied on the stars. ---------- NATS1745 6.0 History of Astronomy, Fall/Winter 2011 Chapter 2 Exam Review ---------- 1. What motivated the imperial astronomers of Ancient China to monitor the skies? Why were they more interested in comets and supernovae than in the planets?  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 events on Earth. It was a type of Astrology. The Ancient Chinese believed that when they saw chaos in sky, chaos was going to happen on earth -> specifically government.  The planets, they understood that planets are normal. They have predictable order/ cycle whereas comets and supernovae don't. They are chaotic. When something unusual happened, like comet and supernovea, there was a sign that something chaotic was going to happen. 2. What produced the Crab Nubula and Crab Pulsar? How do we know that the Crab Pulsar is just over 950 years old?  The Crab Nebula is the debris from a supernova that the Chinese saw explode in AD 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 it’s 950? because pulsar occured when supernovea was born, and we know that the number of years ago of the supernovea marks the date of the pulsar. Know Date of Supernovea know date of it’s pulsar. 3. In what 2 ways does the construction of the Mayan Pyramid of Kukulkan suggest a connection to the sky?  The Mayan Pyramid of Kukulkan had 365 steps, which shows that the Mayans were aware of the Sun’s annual cycle. Also, there was a annual serpent - pattern of light and shades tracked the time of year ( for ex, on the equinoxes, a full serpent’s end appeared at Kukulkan’s head). The pyramid was used as a calendar, because the northern staircase is divided by a short wall, and at the bottom of the wall there is Kukulkan’s snake head. Throughout the year, there was a pattern of light and shadow which moved across the pyramid - created by steps. 4. What do the remaining openings in the Mayan El Caracol suggest that this building was used for?  The opening in the observatory dome was aligned to the North most and South most setting positions of the planet Venus ( which allowed the Maya to measure the duration of Venus’ full path in the sky) 5. What two celestial cycles are tracked in the Dresden codex?  The Dresden Codex describes in detail how the planet Venus moves in the sky; and it includes predictions for its future motion that are accurate to one day in 500 years.  The full eclipse cycle 6. Why did many ancient civilization believe that eclipses are bad omens as well as unpredictable?  Eclipses were believed by many civilizations to be herald of bad times, due to the “damaged” appearance of the sun or moon. If you rely on sun, and suddenly it stars to darken, going to think that it’s bad. Why is it unpredictable? Because eclipses have a long complex cycle. Not a regular cycle. 7. What causes the Moon's phases? What is a lunation?  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).  A lunation is one complete cycle of moon phases. 8. What are the configurations of the Earth, Moon and Sun during New moon, 1st quarter moon, Full moon and 3rd quarter moon? What does a "waxing moon" mean? How about a "waning moon"? Why are crescent moons seen primarily during the day? Why are gibbous and full moons seen primarily at night? What does a "waxing moon" mean? How about a "waning moon"?  When dealing with a full moon that the earth is between the moon and the sun  First quarters and third quarters dealing with a right angle  Waxing moon means that we are seeing increasing amounts of the sun lit sides  Waning moon means that we are seeing less and less of the sun lit sides  Crescent moons are primarily seen during the day because it is on the same side of the sun  When it is gibbous or full we generally see it at night because it’s on the other side of the sky from the sun and when the sun down 9. What is the Moon's phase during a solar eclipse, and what is causing the Sun to darken?  What is the moon’s phase during a solar eclipse; it’s new the moon has to be between the sun and the earth  The moon is blocking the sun If an observer sees a total solar eclipse, where is this observer standing?  The observer is standing in the umbra the total shadow If an observer standing if he/she sees a partial solar eclipse?  They must be standing in the penumbra for a partial solar eclipse looks like a chunk taken out of the sun What does a partial solar eclipse look like? What will the Sun look like if you are standing outside the umbra and penumbra?  If outside of the penumbra they are seeing a perfectly normal sun 10. What is the Moon’s phase during a lunar eclipse, and what is causing the Moon to darken?  Full moon for a lunar eclipse and it is dark b/c it passing through the Earth’s shadow If a total lunar eclipse is seen, what is the Moon passing through?  The moon in its entirety is in the umbra the shadow How about a partial lunar eclipse?  Partially in the umbra and the penumbra How about a penumbral eclipse?  In the penumbra and not in the umbra If an observer on the night side of Earth witnesses a total lunar eclipse, will all observers on the night side of Earth see a total lunar eclipse at the same time?  Yes the eclipses moon appears the same for all observers that is not the case for the sun it is location dependent 11. Why do eclipses not occur every lunation? What do we call the time period when eclipses can occur? On average, how many lunations are there between these time periods? Why are there always at least 1 (or 2) solar eclipses and 1 (or 2) lunar eclipses during these time periods?  Its because that 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 12. Why are lunar eclipses seen more frequently than solar eclipses?  It’s simply because Lunar Eclipses are easier to see. Lunar Eclipses and Solar eclipses occur at same frequency, but to see lunar eclipse you have to be on night side of the earth. To see solar eclipse you have to be in shadow. More regions of the Earth see lunar than solar. 13. In the Dresden codex, what does the repeated occurrence of the numbers '177' and '154' tell us that the Maya understood? What is the significance of the length of the table?  177 and 154 are the six or five lunations and that tells us they when they occurred  Covers the full cycle of eclipses therefore predicts eclipses for eternity (significance) 14. 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 Mayans believed that Venus was their god Kukulkan. This hero, Kukulkan, disappeared in the mountains one day, and then the planet Venus appeared where he disappeared. So the Mayans believed that Venus was the spirit of Kukulkan.  Brightness and wandering motion across the sky 15. What is a "heliacal rise" of Venus? What is it about Venus' appearance at this time that made it a day of worship for the Maya?  1st appearance is brightest and at sunrise ( heliacal rise)  Helical rise of Venus means it rises with the sun. Venus' appearance is unusually bright because its closest to the earth at that phase. that was the day the Maya believed Kukuhlcans spirit was embodied in the planet itself because it appeared this bright right after he disappeared in the mountains 16. When is Venus seen (morning or evening) during the 236 days after its bright heliacal rise?  Venus reappears as a morning star. Is it getting brighter or dimmer, and why?  Dimmer.  b/c it is getting further from the Sun Why does it disappear after this period?  Venus dark side faces Earth. When it finally reappears, is it a morning or evening star?  Venus reappears as an evening star. For the next 250 days, is it getting brighter or dimmer?  Brighter. Why does it disappear again after this period, before its next heliacal rise?  Venus is hidden by glare of Sun. 17. In the Dresden codex, what do the pages containing the rows of 4 Tzolk'in dates represent? What is the significance of the total number of rows in the table?  Each row gives the 4 Mayan dates of the appearances and disappearances in each 584 - day Venus cycle  They represent Venus' appearances and disappearances. Significance is that they are able to predict it for eternity 18. What was the primary motivation for studying the sky in Ancient Egypt?  In Ancient Egypt, survival depended on the annual floorings of the Nile river. The sky was therefore studied for time keeping. The development of astronomy was their need to know their sky in order to track time. Nile river -> flooding -> had to know when it flooded 19. Why do we see different stars and constellations at different times of the year?  its due to the earths annual orbit around the sun 20. Why were the Ancient Egyptians able to use the heliacal rise of Sirius to determine when the Nile river would flood? What was their mythical explanation for the cause of the flood?  When the Egyptian skywatchers saw the brightest star rise in the morning sky just before the Sun, they knew that the Nile was about to flood. This annual inundation covered the land with fresh soil, enabling them to grow another year’s crops.  Sirius, the most brilliant star in the sky, governed the Egyptians’ year. They called the star Sothis, and personified it as the goddess Sopdet. When Egyptians first saw Sothis rising just before the Sun, each July, they knew that the Nile was about swell into its annual life - giving flood - cause, they believed, by Sopdet weeping. 21. Why did the Ancient Egyptians divide the day into 24 hours?  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.The Egyptians understood that if approximately 12 constellations are rising during the night, then 12 constellations are rising in the day. So, the Egyptians defined the 24 hours in a day; 24 hour clock. 22. Why do we add a leap day every 4 years? Who incorporated this rule into our calendar, and from what civilization did he learn this rule from?  While the Earth spins once a day, it’s gradually slowing down all the time. That’s why, every couple of years, we have to add a “leap second” to our clocks. The culprit is the gravity of the Moon, which acts as a brake on our freewheeling planet.  Julius Caesar and he learnt it from the Egyptians  We add a leap day every 4 years so that our calendar year remains synchronized with the earths seasonal year 23. What is the difference between a year in the Julian calendar and a year in the Gregorian calendar? Which calender year is equal to the solar year? Which calendar do we use today?  There is a 11 minute difference and Gregorian calendar is the correct calendar  We use the Greogrian calendar  That one is in sync with the seasons 24. What was the primary motivation for studying the sky in Ancient Babylon? According to the textbook, why did this happen in Babylon but not in Egypt?  In Babylon, where you had the Tigris and Euphrates as very capricious rivers, the whole business of omens and astrology developed. This creates a different kind of religion. The Babylonians turned to all kinds of divination to help them propitiate the gods in the right way. One of which, they turned to the sky. They hoped to take something from the regularity of the heavens in order to understand the irregularity of what was below. 25. Describe (very generally) what we've learned about the Earth's daily spin from the ancient Babylonian records of solar eclipses.  At the moment the Earth’s spin is slowing down 26. From what civilization did we inherit our units of time and angle? (e.g. 60 minutes in 1 hour, 360 degrees in a circle.) Why are there so many 60s in these units?  Along with their meticulous observations of the sky, the 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 ( 6 x 60) degrees around a circle.  babylonians, because they used a base-60 number system; also b/c 60 is an easily divisible number 27. Where are the zodiac constellations? Why were they significant to the Babylonian astrologers? Why can we not see our astrological constellation in the month we were born?  Astrologers were interested which constellations the sun and moon and planets were in in a certain night  Your zodiac sign is defined as the constellation that the sun is in front of in the month one is born. Thus, sun is blocking it.  because your zodiac sign is the constellation that the sun is in front of in the month of your birth. So, during this month, you can't see this constellation, cuz the sky is too bright with the Sun up. 28. For each of the 5 visible planets, what aspect of their appearance was used to choose the Babylonian/Greek god to name them for?  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 colour  Jupiter: ( father of the gods) : named for its brightness and "majestic" motion  Saturn: (god of old age) : named for its faintness and slow motion 29. What are 3 star-like phenomena that match the description of the Star of Bethlehem? Briefly describe each one. Why is it unlikely that the Star of Bethlehem was one of these phenomena?  supernova: the explosive death of a massive star ( can appear as a temporary star: " nova stella" = Latin for "new star")  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)  A supernova, nova or comet is unlikely, as no other civilization recorded a sighting of one around 0 BC. 30. What is the only plausible celestial event to explain the Star of Bethlehem? Describe what this event looks like and why it occurs. Why would such an event have been ignored by the court astronomers in Ancient China?  The only other scientific possibility is a planetary conjunction: when multiple planets line up in the same region of the sky ( not star - like, but a rare and predictable event with astrological importance). Looks like -> planets come together in the sky. Planets are out lapping each other. Reaching similar spots in their orbits.  Assiduous Chinese astronomers would have recorded the appearance of such a brilliant new- sky sight. Instead, the ‘star’ may have been a close approach of Jupiter and Saturn, the astrologically important occultation of Jupiter by the Moon, an unfathomable miracle - or just a myth. The Ancient Chinese Astronomers were only interested in unpredictable events in the sky. A Planetary junction was not something unpredictable. NATS1745 6.0 History of Astronomy, Fall/Winter 2011 Chapter 3 Exam Review ---------- 1. According to the textbook, what was it about Ancient Greece that enabled its philosophers to theorize about why the sky moves the way it does, as opposed to just using it for tracking time and astrology?  Greece was broken up into innumerable valleys and islands. There could be no over-arching control system. Instead, each region developed its small own city state, or polis, the Greek word that gives rise to ‘politics.’ And trade between the city states was in the hands of independent merchants. So Greece developed the world’s first middle class culture. With fluid funds, the prosperous Greek middle class had time on their hands - and freedom to do what they liked with it. The fundamental geography and decentralized rule of Ancient Greece allowed for an intellectual freedom that led to a revolution in scientific thought 2. Why is Thales called the "Father of Science"? According to legend, what celestial event did he successfully predict in order to prove his philosophy?  Considered the "Father of Science" for attempting to find explanations for natural phenomena that didn't involve the gods. Thales apparently made the first accurate prediction of a total eclipse of the Sun, on May 28, 585 BC. 3. What did Anaximander believe about the Earth?  Set the Earth afloat in air. He described how the earth, moon, sun and stars are organized stars. He set the earth afloat-> meaning that he proposed that we are not standing on a ground that stands infinitely beneath on. We are standing on a disk in space. 4. What was Pythagoras proposing when he called the Universe a "cosmos"? What did he propose about the shape of planetary orbits?  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).  He taught that all celestial motion is perfectly circular, and that the Earth is a sphere 5. Who proposed that the Earth is round? Describe 3 observations that suggest this.  Pythagoras proposed that the Earth is round.  Ships gradually disappear on the horizon bottom – first  Earth's shadow on the eclipsed moon is always round  When you travel North or South, the constellations rise and set more rapidly than they would if Earth was flat 6. What did Philolaus believe about the Earth? What did this belief explain about the sky?  He believed that the earth moves.  explains why all celestial bodies rise and set  no need to say that the moon has a monthly component and a daily motion, as well as the sun  the movement of celestial bodies becomes far less complex  earth rotates once a day : but Philolaus thought the earth moves through space once a day  according to him, the central fire is never seen  his argument for that was that only one side of the earth is inhabited  and that side never faces the fire  Philolaus also proposed that between earth and central fire there is anti earth ( never seen ) and the purpose of it was as a protective shield 7. What did Herakleides believe about the Earth?  He set Earth spinning daily around its own axis. He had all the planets orbit around the earth as well. 8. What did Herakleides believe about the motion of Mercury and Venus, and why?  He placed Mercury and Venus in orbit around the Sun to explain the Sun - centered appearance of their motion and their brightness changes 9. What observation allowed Aristarchus to estimate the size of the Moon?  Aristarchus used Earth's shadow on the eclipsed moon to measure the Moon's size relative to Earth's. What measurement in the sky allowed him to estimate the distance of the Sun compared to the Moon's distance?  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 Combining these results, what did he correctly conclude about the relative sizes of the Sun, Moon and Earth (i.e., which is biggest, smallest, etc.)?  His measurements weren't accurate, but he correctly deduced : the Sun is much larger than Earth, and Earth is larger than the Moon What did this conclusion lead Aristarchus to propose about the known Universe?  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. What direction do planets normally move across the sky from night to night? In what direction is a planet moving when it exhibits retrograde motion?  Planets display both direct ( forward )motion ( W to E ) and retrograde ( backward) motion ( E to W). 11. Does a planet's apparent motion appear constant or non-constant in speed, as seen from Earth? What about a planet's brightness?  From Earth the speed of the planets look non-constant is what we see  The brightness also looks non-constant 12. What belief of Plato's directed the objectives of the next generations of Ancient Greek astronomers?  All celestial bodies are perfect unblemished sphere  Constant motions 13. According to Eudoxus, what do the planets reside on in space?  Crystal orbs 14. Why did Eudoxus propose that each planet is carried around Earth by two counter-rotating spheres?  Came up with double sphere model to try and explain 15. In Aristotle's cosmology, what body is at the centre, and what is everything on this body composed of? What is everything outside of this body composed of? What are the qualities of this material?  The Earth is at center  Made of ether quintessence  The Earth is fixed at the centre of the Universe ( geocentric). All matter in the terrestrial realm is composed of four elements : Earth, water, air and fire. 16. What model did Aristotle use to explain the motion of the planets? In this model, what are the shapes of the planetary orbits, and do the planets have constant or non-constant speed through space?  He used Eudoxus’ model  They are circular all the crystal orbs are spheres  They have con
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