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NATS 1745: History of Astronomy Exam Review Questions chapters 1-7

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Department
Natural Science
Course
NATS 1745
Professor
Robin Metcalfe
Semester
Fall

Description
Chapter 1 Questions 1. What celestial event is Newgrange aligned to? Describe what happens at Newgrange on this day. It is aligned to the Winter Solstice, on this day the sunlight will travel up the main passage into the main chamber and then after noon it retreats back down the passage. 2. Describe what happens to the Sundagger on the solstices and equinoxes. During the Winter Solstice two rays of light will frame the large spiral. On the Summer Solstice one ray of light will intersect the large spiral. On the Equinoxes the ray of light will intersect the small spiral. 3. What celestial event is Stonehenge aligned to? Describe what happens at Stonehenge on this day. It is aligned to the Summer Solstice Sunrise; on this day the sun will set right behind the heel stone there. 4. Why do archeoastronomers suspect that Stonehenge's Heel Stone had a missing partner stone? Because everything else in the monument seems to frame up the sun, not hide it. This lead to the belief that there was another stone to help frame up the sun instead of hide it but small shifts in the sun’s rise the past couple thousand years have caused it to rise behind the stone instead of beside it. 5. What causes the Sun to rise and set every day? The earth’s rotation about its axis causes the sun to rise in the East and set in the West. 6. What is the local time for an observer who is directly facing the opposite side of the sky from Sun? What is the local time when the Sun is at its highest point in the sky? What is the local time when the Sun is seen on the Eastern horizon? What is the local time when the Sun is seen on the Western horizon? Midnight, Noon, Sunrise, Sunset. Local sunrise, Local Sunset. 7. What is the azimuth of the noon Sun in the northern hemisphere? How about the southern hemisphere? In the N hemisphere the sun will be South at noon and in the S hemisphere the sun will be North at noon. 8. What does the word "solstice" mean? How does it describe what happens to the Sun's rising and setting positions on the solstices? Solstice is Latin for “solar standstill”. On the summer solstice the rise and set of the sun is moved more north so that it stays in the sky longer, on the winter solstice the arc is moved more south and so has less daylight. 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 Winter solstice it’s azimuth is around SE to SW, for the summer solstice it is around NE to NW and for the equinoxes it is exactly from E to 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? They used stone markers to show where the sun would rise, starting with the winter solstice on the leftmost tower and ending on the rightmost tower six months later on the summer solstice. The winter solstice would have an azimuth of NE and on the summer solstice it would have an azimuth of SE. 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? The winter solstice for the northern hemisphere Is the shortest day because that is the time of year when the axis of the earth is pointed so that the northern hem gets minimal sunlight in its orbit around the sun and spends most of its time in darkness. The summer solstice is the longest day of the year because the axis of the earth points the hemisphere toward the sun most of the day in its orbit around the sun. During the equinoxes there is equal time of daylight and night time. 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 axis of the earth causes the seasons; the axis points the N hem toward the sun for majority of the day on its orbit around the sun during summer. At this time the southern hem is experiencing its winter because it is pointed away from the sun and in darkness majority of the day. 13. Within what latitudes can an observer see the Sun directly overhead? How did these latitudes get their names? Within the tropics (23.5 degrees N or S of the equator) known as the Tropic of Cancer (for the N) and the Tropic of Capricorn (for S). They got their names because at the solstice the sun is where the Cancer and Capricorn constellations are accordingly. 14. What are polar nights and polar days? Within what latitudes do these occur? They are certain times of the year where at the poles there is either 24h of sunlight or 24h of night time. This occurs within 23.5 degrees of the north and south poles. 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? The zenith is the imaginary point directly above an observer. Its altitude is 90 degrees. The horizon has an altitude of 0 degrees. A star half way up in the sky would be 45 degrees. 16. Does a star's altitude and azimuth depend on the observer's location? How about right ascension and declination? Altitude and azimuth are relative coordinates so they depend on the location of the observer. Right ascension and declination are absolute coordinates so they do NOT depend on the location of the observer. 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? The star is 10 degrees north of the Celestial Equator (CE). It is 1h from the sun’s position at 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? If the stars are rotating around our zenith, this means our zenith is the northern celestial pole so we must be at the north pole (latitude of 90 deg N). 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 deg which means the observer is at latitude of 0 deg (equator). When you are south of the equator this point becomes part of the invisible sky below the horizon. 19. If an observer sees Polaris at an altitude of 60 degrees, what is the observer's latitude? The altitude of Polaris seen is equal to the latitude of the observer so the observer would be at 60 deg N. 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? The Polynesians used the star cluster of the Pleiades as the basis. It consists of 8 stars, one of them a red giant. The first half of their year was in December when Pleiades rose as the sun set and the second half of the year was when Pleiades could first be seen in the morning sky. The Andes used this to determine when to plant if the Pleiades were bight and clear; if they were dim and hazy they would delay planting. This is because when El nino occurs, it creates a high altitude cloud that makes the constellation dim. El nino creates a drought in south America which would destroy the crop if they planted it. 21. What did the Polynesian navigators memorize in order to steer their canoes while at sea? The Polynesians memorized star charts; otherwise known as where certain stars would rise and set on the horizon. If they could memorize this, since they do not change they could always use that as a bearing of which direction they are heading in while at sea. Chapter 2 Questions 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. 2. What produced the Crab Nebula and Crab Pulsar? How do we know that the Crab Pulsar is just over 950 years old? Two supernovae resulted in a glowing gas cloud called the Crab Nebula, rapidly spinning relic left from the explosion is the Crab Pulsar. The Chinese were able to figure out the age because it formed when the core of the supernova collapsed, there is a definite date and historical records that give you a good estimate of its brightness Because the pulsar occurred when supernovae was born, and we know that the number of years ago of the supernovae marks the date of the pulsar. 3. In what 2 ways does the construction of the Mayan Pyramid of Kukulkan suggest a connection to the sky? It shows Mayans were aware of sun’s annual cycle 365 steps, annual sepent-pattern of light and shade tracks the time of year (ex on equinoxes full serpent ends at Kulkulcan’s head) 4. What do the remaining openings in the Mayan El Caracol suggest that this building was used for? 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) 5. What two celestial cycles are tracked in the Dresden codex? contains Mayan dates of full eclipse and the venus cycle 6. Why did many ancient civilization believe that eclipses are bad omens as well as unpredictable? They were believed by many civilizations to be heralds of bad times, due to the damaged appearance of the sun or moon, menacing appearance. Long term complex cycle, 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. 7. What causes the Moon's phases? What is a lunation? 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) 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 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? If an observer sees a total solar eclipse, where is this observer standing? If an observer standing if he/she sees a partial solar eclipse? What does a partial solar eclipse look like? What will the Sun look like if you are standing outside the umbra and penumbra? It is a new moon during a solar eclipse, the moon is blocking the sun 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 of the sun 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? If a total lunar eclipse is seen, what is the Moon passing through? How about a partial lunar eclipse? How about a penumbral eclipse? What does a total lunar eclipse look like? How about a partial lunar eclipse? How about a penumbral eclipse? 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? Full moon for a lunar eclipse and it is dark b/c it passing through the Earth’s shadow The moon in its entirety is in the umbra, the shadow Partially in the umbra and the penumbra In the penumbra and not in the umbra 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? 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) 12. Why are lunar eclipses seen more frequently than solar eclipses? Solar eclipses are seen less since the observer must be in the moon’s shadow and lunar eclipses are not location dependent. 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? 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. 177 and 154 are the six or five lunations and that tells us they when they occurred 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. 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? Is it getting brighter or dimmer, and why? Why does it disappear after this period? When it finally reappears, is it a morning or evening star? For the next 250 days, is it getting brighter or dimmer? Why does it disappear again after this period, before its next heliacal rise? After its heliacal rise when it appears the brightest, Venus is seen as a morning star and is dimming. It then disappears due to glare of the sun. It then reappears as an evening star at its dimmest and gets brighter. Once again it disappears because its dark side is facing earth. 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. 19. Why do we see different stars and constellations at different times of the year? Due to earth’s annual orbits 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 - caused, 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 equalintervals. 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 incorporated this and he learned it from the Egyptians. We add a leap day every 4 years so that our calendar year remains synchronized with the earth’s seasonal year 23. What is the difference between a year in the Julian calendar and a year in the Gregorian calendar? Which calendar year is equal to the solar year? Which calendar do we use today? There is a 11 minute difference, We use the Greogrian calendar, it is in sync with the seasons and equal to the solar year. 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 clevermathematics. 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. 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, 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. Chapter 3 Questions 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 as the geographic fragmentation allowed Greek philosophers to theorize about the sky because of its decentralized authority. Wheras the Egyptans & Bablyonians were more closely watched by their governments because of the Nile & Euphrates 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 father of science for attempting to find explanations for phenomena that didn’t involve the gods. He demonstrated that acts of nature like eclipses were predictable, predicted a solar eclipse. 3. What did Anaximander believe about the Earth? He believed it was afloat in the air, explained the universe through the first moving model in which the motion of the celestial bodies is explained by placing them on spinning wheels around the earth 4. What was Pythagoras proposing when he called the Universe a "cosmos"? What did he propose about the shape of planetary orbits? He believed it was a harmonious system that obeyed knowable laws, Cosmos is Greek for harmony or ordered system. He proposed that all celestial motion is perfectly circular and that earth is a spere 5. Who proposed that the Earth is round? Describe 3 observations that suggest this. Pythagoras or his followers proposed this (unclear who), a spherical earth would explain why ships gradually disappear on the horizon bottom first, must be curvature. The shadow on the eclipsed moon is always round, there were never any sharp edges, and when you travel North or South, 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? Believed it rotated once per day around a “central fire” of zeus that inhabited side of earth was never facing, not spinning on its axis. Made the earth airborn to simplify the motion of celestial bodies 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. What did Herakleides believe about the motion of Mercury and Venus, and why? He believed that Mercury and Venus in orbit around the Sun to explain the sun centered appearance of their motion and their brightness changes, Sun orbited around earth. He believed their paths were different than those of other planets, they were more connected to sun’s path 9. What observation allowed Aristarchus to estimate the size of the Moon? What measurement in the sky allowed him to estimate the distance of the Sun compared to the Moon's distance? 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.)? What did this conclusion lead Aristarchus to propose about the known Universe? He used Earth’s shadow on the eclipsed moon during a lunar eclipse to measure the moon’s size relative to Earth. Used the laws of geometry pertaining to circles, used the angle in the sky between the sun and quarter moon to measure the distances relative to each other ended up with moon being half size of the earth (it’s really a quarter). He used Pythagorean theorem to calculate distances. He correctly deduced that the sun is much larger than the earth. This led him to propose that the sun was further away from the earth than the moon (19x further therefore 19x bigger) , leading him to propose a heliocentric model of the universe 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? A planet’s apparent speed is not constant, they appear to speed up and slow down across the sky, a planet appears to brighten and dim as it moves across the sky 12. What belief of Plato's directed the objectives of the next generations of Ancient Greek astronomers? He claimed that all celestial bodies are perfect spheres with constant circular motion so the philosophers after Plato strived to explain how planets’ paths in the sky could be explained by CCM 13. According to Eudoxus, what do the planets reside on in space? Attempted to explain planetary motion by placing the planets on systems of invisible nested spheres “crystal orbs” each spinning with CCM around earth 14. Why did Eudoxus propose that each planet is carried around Earth by two counter-rotating spheres? The two orbs would spin at a different rate giving the planet its daily and night to night motion, this would produce the appearance of retrograde motion while still moving in perfect circle 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? Earth is fixed at the centre of the universe in Aristotle’s cosmology. The universe was divided into the terrestrial and celestial realm, different laws of nature applied. Everything in the terrestrial realm is composed of four elements: earth water air and fire. All bodies in the celestial realm are perfect spheres th and composed of a pure and imperishable substance called “quintessence” (5 element) or ether (pure air) 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 orbs containing a system of nested orbs, the daily motion of which is driven by a single outer orb 17. How did Aristotle explain the daily motion of the sky? A single orb would spin daily giving all the celestial bodies their daily motion 18. What was Aristotle's explanation for the source of all motion in the Universe? “Whatever is moved must be moved by another” the motion of the orbs is supplied by
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