Astronomy 191 Chapter 1

AST 191

Chapter 1

Question 1: What do we mean by a geocentric universe? Contrast a geocentric view with our modern view of the universe.

Answer 1: The theory that everything in our universe orbits around the earth. The earth is the center of the universe. The geocentric model is also known as the Ptolemaic system. In the geocentric view it was assumed that the Earth was the center and everything evolved around it, the stars, sun, moon. The geocentric view was believed in ancient times. The modern view replaced the geocentric view when Copernicus and Galileo discovered that actually the Earth evolved around the Sun

Question 3: What do we mean when we say that the universe is expanding? How does expansion lead to the idea of the Big Bang?

Answer 3: The universe has been spreading out over time since the Big Bang. The individual galaxies are moving closer together due to gravity. The average distance between galaxies is expanding which means they at one time were tightly together. If we calculate the separation per year, we are able to determine that at one time we were one universe, which is when the Big Bang occurred.

Question 4: What did Carl Sagan mean when he said that we are “star stuff”!

Answer 4: Carl Sagan meant that all elements and particles in the universe ultimately come from stars.

Question 5: How fast does light travel? What is a light year?

Answer 5: Light travels at a speed of 300,000 kilometers per second. This speed is comparable to light circling the Earth- eight times in 1 second. A light year is 10 trillion kilometers or 6 trillion miles.

Question 11: Define astronomical unit, ecliptic plane, and axis tilt. Explain how each is related to Earth’s rotation and/or orbit.

Answer 11:

Astronomical Unit: This is the Earth’s average orbital distance equal to 150 million kilometers.

Ecliptic Plane: This is the reference point for defining the orbital path of other objects in the solar system.

Axis Tilt: Is...