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Physical Science Ancient Greek Physics and Astronomy
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Physical Science
Ancient Greek Physics and Astronomy
Challenges to the Ptolemaic model of the Universe
Tycho Brahe and Kepler’s Three Laws of Planetary Motion
Physics – natural and physical science that involves the study of matter and its motion through space and time, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.
Early Ideas of Motion and Matter
Aristotle, the foremost Greek scientist, studied motion and divided it into two types: natural motion and violent motion. Natural motion on Earth was thought to be either straight up or straight down.
Voluntary motion refers to the ability of human as well as animals to move because they have the will or the capacity to do so. Involuntary motion refers to the motion cause by unnatural condition. Natural motion, voluntary motion and involuntary motion are the three terrestrial motions.
Ancient Greek also explained the motion of heavenly bodies. The observable motion of the object you see in the sky are collectively termed as non-terrestrial motions. The movement of different celestial bodies can be described as diurnal motion, annual motion, and precession of the equinoxes.
Diurnal Motion
Diurnal motion is the apparent daily revolution of the celestial sphere around the celestial poles as a direct effect of the Earth’s rotation on its axis. In other words, it refers to the apparent movement of stars and other celestial bodies around Earth. The circular path that the celestial bodies take to complete the diurnal motion is called diurnal circle.
Annual Motion
Annual motion is the apparent yearly movement of the stars as observed from Earth as a direct effect of the Earth’s revolution around the sun.
Precession of the Equinoxes
Precession of the equinoxes is the apparent motion of the equinoxes along the ecliptic as Earth ‘wobbles,’ and this motion happens about every 26 000 years. At present, Earth’s North Pole points to Polaris. However, it will eventually point to another star, Vega, because of precession.
Observations Leading to the Belief that the Earth is Round.
The idea of a spherical Earth was floated around by Pythagoras around 500 BC and validated by Aristotle a couple centuries later. Anaxagoras, a Greek philosopher of nature remembered for his cosmology and for his discovery of the true cause of eclipses which supported Pythagoras observations during al lunar eclipse that the Earth’s shadow was circular.
The North star was believed to be at fixed position in the sky. However, when the Greeks traveled to places nearer the equator, they noticed that the North star is nearer to the horizon. Aristotle argued that such observations is only possible if Earth is round.
If the Earth is flat, the ship travelling away from an observer should become smaller and smaller until it disappeared. Instead, the Greeks observed that the ship’s hulled disappeared first, which implied that the surface of the Earth was curved.
Simultaneously measuring the length of the shadows cast by identical poles perpendicular to a flat surface that is tangential to the earth's radius at various, distant locations. If indeed the earth is round, then the shadows should all vary in length from one distant location to another. This means that the angle at which the parallel rays of sunlight struck each pole varied from one location to another. (Recall the alternate-angles theorem from Geometry class) If the earth is flat, then the lengths of all the shadows should be identical when measured simultaneously, since all rays of sunlight that strike the earth are parallel. However, they are not identical, but in fact, vary in such a way that the angles indicate a spherical surface.
Astronomical Observations Before the Invention of Telescope
Even before the advent of the telescopes, ancient astronomers were able to observe the:
rising and setting of the Sun in the east and the west, respectively,
point where the Sun rises and sets in the horizon varies in a year,
phases of the moon,
lunar eclipse,
solar eclipse,
daily and annual motion of the stars, and
planets Mercury, Venus, Mars, Jupiter, and Saturn.
Models of the Solar System
There are most popular models of the solar system. These are the Ptolemaic, Copernican, Tychonic models.
Physical Science Ancient Greek Physics and Astronomy
Course: BS Psychology
University: Polytechnic University of the Philippines
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