Greek Theories on Earth's Sphericity

Study Notes

Anaxagoras
- Attempted to provide a scientific understanding of eclipses, meteors, rainbows and the Sun, describing it as a mass of blazing metal.
- Believed that the Sun was a hot rock, and the Moon shone from the reflected light of the Sun.
- Explained eclipses as the Moon passing through the Earth's shadow (lunar eclipse) or the Moon passing between the Sun and the Earth (solar eclipse).
Aristotle
- Provided observational evidence for the Earth being spherical.
- Noted the circular shape of the Earth's shadow during a lunar eclipse, which would be oval if the Earth was flat.
- Observed that the North Star's position appeared closer to the horizon when travelling towards the equator, suggesting a curved Earth.
- Observed that ships sailing away from the horizon first disappeared hull first then the sails, implying that the Earth was curved.
Eratosthenes
- First to calculate the Earth's circumference.
- Calculated the tilt of the Earth's axis.
- Both calculations were remarkably accurate for their time.

Greek philosophers believed in a geocentric model, with the Earth at the center of the Universe.
Eudoxus, Aristotle, and Ptolemy were proponents of the geocentric model.
Aristarchus and Copernicus were proponents of the heliocentric model, with the Sun at the center of the Universe.

Tycho Brahe was a Danish nobleman, born in 1546.
Brahe became interested in astronomy after witnessing a predicted solar eclipse.
King Frederick II funded the construction of Brahe's observatory near Copenhagen.
Brahe's observations were made before the invention of the telescope.
Brahe made several groundbreaking discoveries:
- Supernova explosion of 1572.
- Observation of a comet in 1577.
- Collected extensive and precise astronomical data on the locations and orbits of celestial bodies.
Johannes Kepler, a German astronomer, mathematician, and astrologer, was hired by Brahe to analyze his data.
Kepler inherited Brahe's data set after his death, which was crucial for developing his Three Laws of Planetary Motion.
Kepler's Three Laws of Planetary Motion:
- Law of Ellipse: Each planet orbits the Sun in an elliptical path, with the Sun at one focus.
- Law of Equal Areas: The imaginary line connecting the Sun and a planet (radius vector) sweeps out equal areas in equal times as the planet orbits.
- Law of Period: The square of the period of a planet's revolution around the Sun is proportional to the cube of its average distance from the Sun.

The experiment involves using a paper plate, popsicle sticks, scissors, tape, and a flashlight.
The experiment aims to demonstrate how the shape of the Earth casts a circular shadow during a lunar eclipse.
First, the paper plate is held vertically in front of the flashlight, and the shadows of the popsicle sticks are observed.
Then, the paper plate is slightly bent, and the shadows are observed again to compare the results.
The experiment helps students understand how different shapes cast shadows, which can be related to the Earth's spherical shape.