Path of the Sun project: Capri, Amy, Courtney?

Where someone says, or you read, that “the sun is overhead at midday” is this strictly correct?

Review: Eclipses

What type of eclipse would be seen by observers on the night side of the earth in this diagram?

A) Total solar eclipseB) Total lunar eclipseC) No eclipseD) Partial lunar eclipse

And what is wrong with the way this picture is drawn?

Moon Phases: putting it all together

Another demo, with everyone out of your seat! Time for “moon balls” demonstration

If tonight the moon is full when it rises in the east, what phase will it be when it sets in the west?

A) FullB) last quarterC) New moonD) First quarter

Lecture tutorial, p.81, Cause of moon phase

Now, back to motions of the Planets: Copernicus and Circles

Copernican theory: planets revolve around the sun, not around the earth

Let’s watch what you might observe for Venus, Mars

http://astro.unl.edu/naap/ssm/animations/configurationsSimulator.html

This was before the telescope, so no ideas about what planets actually looked like – just points, like stars

Lecture-tutorial, p. 99, Observing Retrograde motion

Digress: what is a theory?

The word "theory" means something very different in everyday language than it does in science: to the average person, a theory is just an idea…

A scientific theory is an explanation of something that has been demonstrated through repeated experiments or testing.

A scientific theory can also make predictions that can be tested

What can we predict about the appearance of Venus when seen through a telescope?

Galileo was the first to look at planets through a telescope. These are views of Venus at different points in its orbit:

And again…

Kepler: planets move in almost circular orbits

Kepler lived at the same time as Galileo, both born shortly after Copernicus published his book. He used the careful observations made by Tycho Brahe to modify Copernicus’ idea of circular motion.

He realized, from the orbit of Mars, that the planets move not on circular, but in elliptical orbits.

You will also have a chance to explore these in a computer lab. The web page looks like this:

http://astro.unl.edu/naap/pos/animations/kepler.html

Simulator, Worksheet for Kepler’s Laws

Review…

1. Planets orbit sun in ellipse

2. Line connecting sun and planet sweeps out equal areas in equal

3. Period (“Year”) squared = semi-major axis cubed

Kepler : provided understanding of motions of planets, and thus, every other body in the universe in his three laws

Wdefine the astronomical unit (a.u.), as the distance from the sun to the earth

Next : Isaac Newton, explained Kepler’s

laws

Breakthroughs in mechanics, optics, gravity, mathematics (invented calculus)