Shape & Motion in the Sky

These flashcards cover key concepts related to the motion of celestial bodies and historical models of the universe.

What causes Diurnal Motion?

The daily motion of Earth on its axis.

What is Annual Motion?

The yearly revolution of the Earth around the Sun.

What is the ecliptic?

The sun's path across the sky throughout the year.

What is Precession of Equinoxes?

The slow, cyclical wobble of Earth's axis of rotation.

How did the Greeks demonstrate the Earth is spherical?

By observing that the tops of ships' masts appear first when approaching and disappear last when leaving.

What was Thales of Miletus' model of the universe?

Proposed that Earth was a flat disk floating on a vast expanse of water.

What model did Anaximander propose?

A cylindrical model of the Earth that was stationary at the center of the universe.

What is the key concept in Herakleides' model?

A spherical Earth that rotates on its axis with Mercury and Venus revolving around the Sun.

What groundbreaking idea did Aristarchus of Samos present?

A model where the Sun is at the center of the universe with all planets orbiting it.

What phenomenon puzzled ancient astronomers?

Retrograde Motion, the apparent backward movement of a celestial object.

How did Plato address the constraints in retrograde motion?

By modeling planetary orbits as circular and moving at constant speed, though he couldn't fully explain retrograde motion.

What method did Eudoxus use to explain planetary motion?

He used geometry to create a model that explained the irregular motion of planets while maintaining the idea of circular motion.

What did Aristotle believe about the universe's structure?

That the Earth was the center of the universe and surrounded by concentric spheres.

What was the significant contribution of Claudius Ptolemy?

His model featured a stationary Earth at the universe's center, explaining planetary motion through epicycles and deferents.

What did Copernicus propose in his heliocentric model?

That the Sun is at the center of the universe and that the Earth rotates on its axis while orbiting the Sun.

What observation did Galileo make that supported Copernican theory?

He observed Venus going through a full set of phases, ruling out the Ptolemaic system.

What was Tycho Brahe known for?

Extensive and accurate observations of planets and stars without a telescope.

What is the significance of Johannes Kepler's Laws of Planetary Motion?

They describe planetary orbits as elliptical and detail relationships between distance and orbital period.

What is Kepler's First Law of Planetary Motion?

Planets orbit the Sun in elliptical paths, with the Sun at one focus of the ellipse.

What does Kepler's Second Law state?

A line joining the Sun and a planet sweeps out equal areas in equal times.

What is the formula related to Kepler's Third Law?

The square of the orbital period is directly proportional to the cube of the average distance from the Sun.