The Copernican Revolution - Flashcards

A set of Question-and-Answer flashcards covering key concepts from The Copernican Revolution lecture notes, including epicycles, heliocentric model, observations by Galileo and Brahe, Kepler's laws, Newtonian gravity, eclipses, and long-term changes in Earth's tilt.

Why did Ancient Greeks use epicycles to describe planetary motion?

To explain the planets' apparent complex motions and retrograde loops within a geocentric framework.

What are the basic features of the Copernican heliocentric model?

The Sun is at the center of the solar system; planets orbit the Sun; Earth is not the center of the universe (originally with circular orbits).

What was Tycho Brahe's major contribution to astronomy?

He made highly accurate naked-eye measurements of planetary positions and built Uraniborg, providing data used by Kepler.

What telescope-based observations by Galileo challenged the geocentric model?

Moons around Jupiter, mountains on the Moon, phases of Venus, and sunspots with solar rotation.

What is Kepler's First Law?

Planetary orbits are ellipses with the Sun at one focus.

What is Kepler's Second Law?

The line from the Sun to a planet sweeps out equal areas in equal times.

What is Kepler's Third Law?

The square of a planet's orbital period is proportional to the cube of its semimajor axis.

What does Newton's Law of Gravitation state?

The gravitational force between two masses is proportional to the product of their masses and inversely proportional to the square of the distance between them: F = G M m / r^2.

What is an astronomical unit (AU)?

The average distance between the Earth and the Sun; a standard unit of length in the solar system.

Why don't we see total solar eclipses at every New Moon?

Because the Moon's orbit is tilted relative to Earth's orbit; eclipses occur only when alignment happens near the nodes and the path of totality is narrow.

What is the difference between the umbra and the penumbra in eclipses?

Umbra is the full shadow (total eclipse); penumbra is the partial shadow (partial eclipse).

What causes a lunar eclipse?

Earth lies between the Moon and the Sun; the Moon passes through Earth's shadow and may be partial or total.

What is the approximate tilt of the Moon's orbit relative to the Earth's orbit around the Sun?

About 5 degrees.

What is a total solar eclipse?

When the Moon completely blocks the Sun as seen from a location on Earth, casting the Moon's umbra on Earth.

What did Galileo observe to show the heavens are not perfect or unchanging?

Moon mountains/craters, Sunspots and rotation, and Jupiter's moons with Venus showing phases.

What happened to Galileo after he supported heliocentrism?

He was arrested for heresy, forced to recant, and placed under house arrest; later acknowledged by the Church and apologized in later years.

Who proposed the heliocentric model and who refined planetary orbits into ellipses?

Copernicus proposed heliocentrism; Kepler refined with elliptical orbits.

What did Newton contribute to modern astronomy?

The Principia established universal gravitation and the laws of motion to explain why planetary motions occur.

What was Ptolemy's contribution to the geocentric model?

A geocentric model with epicycles and deferents to explain planetary motion, used for centuries.

What is an epicycle?

A small circle whose center moves along a deferent, used to explain retrograde motion in the geocentric model.

What was Copernicus's major change in the solar system?

Moved the Sun to the center and re-centered planetary orbits around the Sun.

What are perihelion and aphelion?

Perihelion is the closest point of a planet's orbit to the Sun; aphelion is the farthest.

What is precession in the context of Earth's axis?

A long-term wobble of Earth's rotation axis causing pole stars to change over millennia (e.g., Polaris, Vega, Thuban).