Ask Dr. Jay
If you have any questions about the course, feel free to ask the author of the book! You have to register in order to ask questions, but registration is free, and we won’t share your information with anyone.

Links for the Fifteenth Chapter

How Gravity Keeps the Planets in Orbit around the Sun
This video gives a good discussion of why planets orbit the sun and don’t fall into the sun. The same reasoning works for the moon and the earth.

Solar System Model
This is a great model that shows you the proper scale of the solar system and how all the planets move relative to the sun. You zoom in and out with the mouse wheel, you can slow the motion or speed it up. You can even click and grab a planet to move it and see how the other planets move in relation to it.

The Relative Sizes of the Planets and Some Stars
This video goes through our planets, the sun, and other stars in the universe, showing you their relative size.

Comets
This video discusses the basics of comets and gives some pictures of famous ones.

Retrograde Motion
This animation has no narration, but gives you great visuals for retrograde motion.

Ptolemy’s model of the universe
This animation has no narration, but it shows you how epicycles worked in the geocentric view of the universe.

Mars’s Opposition
This animation explains how opposition occurs. Notice that Mars is much closer to the earth at opposition than at other times, which is why it is brightest at opposition.

Spectroscopy of the Sun
This video shows how we read the from a star and determine what it is made of. It ends with spectral classification, which you don’t need to know.

Nuclear Fusion in the Sun
This video explains how fusion powers the sun.

Sunspots
This video shows sunspots and how they are analyzed.

Solar Flares
This video shows good animations of solar flares.

The Difference Between CMEs and Solar Flares
This video has no narration, but allows you to see the difference.

The Moon’s Phases
This video has a great demonstration of why the moon has phases. There are other facts given, but the best part is the part about phases.

Earthrise: The 45th Anniversary
This is an incredible recreation of how the famous “earthrise” picture in the book was taken.