Three important ideas developed by the ancient Greeks
- models of nature
- mathematics
- theories pertaining to observations
Thales (624-546 BC)
Philosophized about what is the universe made of. Believed the Earth is a flat disk floating in an infinite ocean.
Anaximander (610-546 BC)
Invented the idea of the celestial sphere
Pythagoras (560-480 BC)
First said the Earth is round
Democritus (470-380 BC)
Proposed that the world is built from individual atoms.
Plato (428-348 BC)
Proposed that heavenly objects move in perfect circles at constant speeds.
Aristotle (384-322 BC) and Ptolemy (100-170 BC)
Proposed an Earth-centered universe (geocentric modeling)
Heraclides (388-315 BC)
First to suggest Earth rotates
Aristarchus (310-230 BC)
First to suggest Earth orbits the Sun.
Eratosthenes (240BC)
Measured the size of the Earth using a heliocentric model.
Hipparchus (190-120 BC)
Predicted planetary motion, discovered precession, and invented the magnitude system.
Copernicus (1473-1543)
Proposed a heliocentric model of the universe, but still in perfect circles.
Brache (1543-1601)
Developed Naked-eye observatories
Kepler (1571-1630)
First to figure out that planetary orbits are ellipses, matching Brache's data.
Semi-Major axis (Ellipse)
Half of the long axis of the Ellipse
Semi-Minor axis (Ellipses)
Half of the short axis of the ellipse
Eccentricity (Ellipses)
Describes how stretched an ellipse is relative to a perfect circle
Kepler's first law of planetary motion
The orbit of each planet about the sun is an ellipse, with the sun at one focus
Kepler's second law of planetary motion
A planet moves faster on the part of it's orbit nearer to the sun and slower when it moves farther away, sweeping equal areas within the ellipse in equal amounts of time
Kepler's third law of planetary motion
More distant planets orbit the sun at slower average speeds.
P² = a³
P is the orbital period in years
a is the average distance from the sun in AU
Perihelion
The point on an eclipse when a planet is closest to the star.
a(1 - e)
Aphelion
the point on an Ellipse when a planet is farthest from the star.
a(1 + e)
Earth is closer to the sun in January than July. Which of the following is true?
- A. Earth travels faster in July than January
- B. Earth travels faster in January than July
- C. It is summer in January and winter in July
- D. None of the above
- B. Earth travels faster in January than July