Lecture 3 Flashcards
(11 cards)
How do planets move relative to the background stars?
Planets move steadily across the night sky but can exhibit retrograde motion, appearing to move backward relative to the background stars due to their orbits around the Sun.
What is the geocentric model?
The geocentric model places Earth at the center of the universe, with all planets, including the Sun, orbiting around it. Venus and Mercury are positioned between Earth and the Sun.
What is the heliocentric model?
The heliocentric model places the Sun at the center of the solar system, with planets, including Earth, orbiting the Sun. It naturally explains retrograde motion as a feature of planetary orbits.
What is retrograde motion, and how is it explained in a heliocentric system?
Retrograde motion is when a planet appears to move backward against the background stars. In a heliocentric system, this occurs when Earth overtakes an outer planet like Mars in its orbit, causing the planet to appear to move backward.
What role did Copernicus play in determining the layout of the solar system?
Copernicus proposed the heliocentric model, placing the Sun at the center and suggesting that planets orbit the Sun. His model required fewer epicycles than the geocentric model but still used circular orbits.
What contributions did Tycho Brahe make to astronomy?
Tycho Brahe provided meticulous and accurate naked-eye measurements of planetary positions, which were essential for developing more accurate models of the solar system.
How did Kepler improve upon the Copernican model?
Kepler used Brahe’s data to show that planets move in elliptical orbits, not circles, and formulated three laws of planetary motion, eliminating the need for epicycles.
What were Galileo’s key discoveries using the telescope?
Galileo discovered the phases of Venus, moons of Jupiter, rings of Saturn, craters on the Moon, and sunspots, all of which supported the heliocentric model.
Why are Venus and Mercury never visible all night long?
Venus and Mercury are always close to the Sun from our perspective, so they are only visible just after sunset or just before sunrise.
How do Venus and Mercury show phases in a heliocentric solar system?
Venus and Mercury show phases similar to the Moon because they orbit the Sun. They appear “full” when on the far side of the Sun and “crescent” when between Earth and the Sun.
How did Newton explain the motion of planets?
Newton’s laws of motion and universal gravitation explained why planets move in ellipses (Kepler’s first law) and how their speed varies (Kepler’s second law), providing the physical basis for Kepler’s laws.
