# When is noon?

I was at the zoo this weekend, it was fun but hot. Somewhere near the middle, there was a sun dial. The cool thing (well, I think sun dials are cool anyway) was that the shadow was pointing about to the “12”. I looked at my watch and it said 1:05 PM. What is up…

# RP 9: Error propagation and the distance to the Sun

Some time ago, I wrote about the awesome things the Greeks did in astronomy. Basically they calculated the size of the Earth, distance and size of the moon and distance and size of the sun. The value obtained for the distance to the sun was a bit off, but still a bang up job if…

# RP 7: Cool things the Greeks did in astronomy

One of things I like to think about in science is “how do we know that?” It is interesting how one thing builds on another. This is a story of how the Greeks estimated the distance from the Earth to the Sun (an important idea in the development of the model of the solar system).…

# Scale Model of the Solar System

The solar system is difficult to show correctly. Why? It is difficult because the size of things are vastly different. Let me use units common in solar-system astronomy, the Astronomical Unit (or AU). One AU is the distance from the Sun to the Earth. If I want to look at all the planets, I would…

# Parallax, what is it good for?

Very simply, parallax is an apparent motion of an object due to a change in observation position. Let me start with an example. Here are two photos. I took a picture of the cabinet in the background from two slightly different positions. In the foreground is a clone trooper that did not actually move. I…

# Seasons, short and simple

I love this question: Why is it warmer in the summer than in the winter (for the Northern hemisphere)? Go ahead and ask your friends. I suppose they will give one of the following likely answers: The tilt of the Earth The tilt of the Earth makes us closer to the Sun We are closer…

# Error propagation and the distance to the sun

Some time ago, I wrote about the awesome things the Greeks did in astronomy. Basically they calculated the size of the Earth, distance and size of the moon and distance and size of the sun. The value obtained for the distance to the sun was a bit off, but still a bang up job if…

# When is the Sun directly overhead?

Question: When is the Sun directly overhead? (assume you are in the United States of America) Common Answers: Everyday at noon. On the summer solstice (June 21ish) Answer: For continental U.S. the answer is never. Since the Earth’s rotation axis is tilted 23.5 degrees with respect to its orbital motion around the Sun, one would…

# Cool things the Greeks did in astronomy

One of things I like to think about in science is “how do we know that?” It is interesting how one thing builds on another. This is a story of how the Greeks estimated the distance from the Earth to the Sun (an important idea in the development of the model of the solar system).…

# Status of Pluto – Zombie Feynman Replies

I can’t believe there is still all this talk about what to call Pluto. Can’t we just move on? In an effort to help, I have summoned the Zombie Feynman to get his words on the subject. This is what he said: