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
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
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?
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?
What is the local time when the Sun is seen on the Western horizon?
7. What is the azimuth of the noon Sun in the northern hemisphere? How about the southern
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
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
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
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-
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
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
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
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
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?
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?
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
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
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
babylonians, because they used a base-60 number system; also b/c 60 is an easily divisible
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
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
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
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
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
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
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
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
13. According to Eudoxus, what do the planets reside on in space?
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