Podcast
Questions and Answers
Which observation did ancient Greeks use to support the idea that the Earth is curved?
Which observation did ancient Greeks use to support the idea that the Earth is curved?
- The appearance of new stars when traveling east to west.
- The consistent shape of constellations throughout the year.
- The way birds migrate annually.
- Ships disappearing hull first over the horizon. (correct)
How did Aristotle's observations contribute to his conclusion that the Earth and other heavenly bodies are spherical?
How did Aristotle's observations contribute to his conclusion that the Earth and other heavenly bodies are spherical?
- He tracked the movement of planets relative to the stars.
- He observed that different stars are visible from different latitudes. (correct)
- He noted that solar eclipses always produce a circular shadow.
- He measured the Earth's circumference using shadows.
What was the fundamental principle behind Eratosthenes' method for calculating Earth's circumference?
What was the fundamental principle behind Eratosthenes' method for calculating Earth's circumference?
- Calculating the distance to the moon during a lunar eclipse.
- Comparing the angles of shadows in two different cities. (correct)
- Measuring the time it takes to circumnavigate the Earth.
- Using triangulation based on the height of mountains.
Which aspect of lunar eclipses supported the ancient Greek understanding that the Earth is spherical?
Which aspect of lunar eclipses supported the ancient Greek understanding that the Earth is spherical?
What reasoned argument did Aristotle make, assuming a geocentric model of the universe?
What reasoned argument did Aristotle make, assuming a geocentric model of the universe?
How did the changing position of constellations in the night sky, as people traveled north or south, suggest a curved Earth?
How did the changing position of constellations in the night sky, as people traveled north or south, suggest a curved Earth?
What was unique about the element that Aristotle claimed the heavens were made up of?
What was unique about the element that Aristotle claimed the heavens were made up of?
What geometrical shape would result if enough materials accumulated on the surface of the earth?
What geometrical shape would result if enough materials accumulated on the surface of the earth?
What evidence did the ancient Greeks use regarding shadows, to argue that the Earth could not be flat?
What evidence did the ancient Greeks use regarding shadows, to argue that the Earth could not be flat?
What two cities did Eratosthenes compare on Earth, to make his geometrical calculations about the circumference of the planet?
What two cities did Eratosthenes compare on Earth, to make his geometrical calculations about the circumference of the planet?
Flashcards
Three Key Observations
Three Key Observations
Ships disappear over the horizon, horizon becomes further away, constellations change north/south, curved shadow on moon during lunar eclipse.
Pythagoras's Earth Shape
Pythagoras's Earth Shape
First to propose the Earth was round based on traveler's tales of ships and the shifting position of stars when traveling north.
Aristotle's Spherical Earth
Aristotle's Spherical Earth
Observed different stars visible in Egypt versus Cyprus, concluding all heavenly objects, including Earth, must be spheres.
Aristotle's Argument 1 for Spherical Earth
Aristotle's Argument 1 for Spherical Earth
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Aristotle's Argument 2 for Spherical Earth
Aristotle's Argument 2 for Spherical Earth
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Aristotle's Argument 3 for Spherical Earth
Aristotle's Argument 3 for Spherical Earth
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Aristotle's Argument 4 for Spherical Earth
Aristotle's Argument 4 for Spherical Earth
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Eratosthenes
Eratosthenes
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Study Notes
Three Key Observations
- Travelers tales of ships disappearing over the horizon and that the horizon became further away.
- Different constellations are visible when traveling north or south.
- The Earth casts a curved shadow on the moon during lunar eclipses.
Ancient Greeks
Pythagoras
- First proposed that the Earth was round based on travelers' tales of ships.
- The shifting of stars to a higher position in the sky as one journeyed north suggested a curved Earth.
Aristotle
- Observed stars seen in Egypt that could not be seen in Cyprus.
- Concluded that all heavenly objects, including the Earth, must be spherical.
Argument 1
- The sphere is a perfect solid, and the heavens are regions of perfection.
- Aristotle used a geocentric model because the Earth is the center of the universe.
- Aristotle stated perfect solids and the heavens were symmetrical, had the same center, and were made up of a different element (ether).
- The universe was made up of concentric spheres, with Earth at the center and the heavens beyond.
- The heavens are a higher state of being and are, therefore, more perfect than the Earth.
Argument 2
- Earth's component pieces fall naturally towards the center due to gravitational pull/force.
Argument 3
- During an eclipse of the moon the Earths shadow is always circular and a flat disc would cast an oval shadow.
- Lunar eclipses, specifically the Earth's shadow cast on the moon, were used as evidence.
- A flat penny produces a circular shadow if held properly in sunlight.
- A flat penny produces an entirely different shape if rotated 90 degrees to the sunlight.
- Only a sphere shows a consistent curvature, therefore the Earth must be a sphere.
Argument 4
- The pole star appears higher in the sky in short travels northwards.
- Moving to new lands (both north and south of Greece), observers observed changes in the sky such as changes in the altitude of stars and even new stars appearing in the local horizon.
- A flat Earth would mean all observers would see the same local horizon, which they do not, therefore supporting a spherical Earth.
Erastosthenes
- Together with Aristarchus, they calculated the circumference of the Earth.
- He was the first person to determine the circumference of the Earth.
- Erastosthenes combined geometrical calculations with physical observations.
- He produced a surprisingly good measurement using a simple scheme that combined geometrical calculations with physical observations.
- He calculated the circumference of the Earth from a simple observation about the shadows cast in a well in two distant cities, Syene and Alexandria.
- Realized that through simple geometry, he could estimate the size of the entire Earth if he knew the distance between these two cities.
- 7.2°/360° = 800km/Xkm
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