Astro 1500 Trivia - January 31, 2025

The star Vega is 25 light years away. When did the light that is now reaching us leave Vega?

• 1975

• 2021

• 2001

• 2025

Answer explanation

A light year is the distance that light travels in a year. Thus, since Vega is 25 light years away, it took light 25 years to reach us. The current date is 2026, and so 25 years ago was 2001.

How old is the Universe?

• 100,000 years

• 100 million years

• 4.5 billion years

• 13.8 billion years

According to modern science, what determines our understanding of the Universe?

• Philosophical thought

• Empirical evidence

• Divine revelation

• Intuition

Answer explanation

Empirical evidence is the key to everything in science.

What is stellar parallax?

• Planets moving in the sky because of their orbit

• A way to prove the geocentric model

• Shifts in the relative positions of stars in the sky because of movements of the Earth

• The "solution" to retrograde motion

Answer explanation

Stellar parallax is the slight change in the star's position in the sky compared to other stars because of the movement of Earth.

What feature of the Geocentric/Ptolemaic model explained retrograde planetary motion?

• Epicycles

• It didn't; that was one of its main flaws

• Circular orbits around the Earth

• The planets would sometimes just move backward

Answer explanation

In order to make their model fit the data, they had to add epicycles upon epicycles. This led to a very complex model!

What in the Copernican/Heliocentric model of the Solar System explained retrograde motion?

• This model doesn't explain retrograde motion without modification--that's why it took so long to gain traction

• Epicycles

• Planets just move backward sometimes

• It was a natural part of the model--planets passing each other create this phenomenon

Answer explanation

As Earth orbits faster than Mars, it will pass by it, causing Mars to move backwards (compared to the background stars) from Earth's point of view.

What was considered a major flaw of the heliocentric model back around the time it was first proposed?

• Stellar parallax was not observed

• It did not explain retrograde motion

• It poorly predicted planetary positions

• The sun was made out to be too massive

Answer explanation

Stellar parallax was not observed, even though it was predicted. The solution to this is the subject of the next question.

Why wasn't parallax observed when Copernicus proposed his heliocentric model?

• The stars are so far away that very sensitive instruments are needed to detect parallax

• Apparently moving stars were mistaken to be other planets

• The sun made it impossible to observe stars over a whole year

• It was, but proponents of the geocentric model blamed it on atmospheric distortion

Answer explanation

The parallax of even nearby stars is so small that a telescope is needed. Observing the parallax of one of the nearest stars (Alpha Centauri) is equivalent to trying to see a quarter coin on I-35 while standing in Jack Trice stadium!

What is the Copernican Revolution?

• An attempt by Copernicus to overthrow the Polish government

• The transition from a geocentric model to a heliocentric model

• The transition to choosing the simplest explanation as the most likely

• The transition from using thought and intuition to acquire knowledge to instead using empirical evidence

What was said in Kepler's first law that disagreed with both the geocentric model AND Copernicus's heliocentric model?

• The size of a planet's orbit and its orbital period are related

• The sun is the most massive thing in the solar system

• Planets orbit in elliptical orbits

• Planets closer to the sun move faster