Seasons, Tides, and Phases of the Moon

J. C. Sprott

Department of Physics

University of Wisconsin

Madison, WI 53706

Presented to the

Green County Science Teachers’ Workshop

on February 25, 2000

Science Literacy Over 200 studies document

scientific illiteracy. Scientific illiteracy hurts

Nation and individuals. Teachers are uncomfortable

teaching science. Science has fallen out of

favor. We have a public-relations

problem.

What causes the seasons?

Earth Sun

How many times does the earth rotate about its axis in a year?

EarthSun

365.242 + 1 = 366.242

As seen from the North Pole, which direction does the earth rotate?

EarthSun

Counter-clockwise

How do we know the earth is rotating?

Foucault Pendulum (1851)

Coriolis Effect

Wind Patterns

Projectile Deflection

How do we know the earth orbits the sun? Annual Parallax of the

Stars (1837) - nearby stars appear to move

Aberration of Starlight (1727) - change in apparent direction of stars, cf: raindrops

What causes the phases of the moon?

MoonEarth

Sun

When you observe a crescent moon in the evening, do the tips point left or right?

West

Facing South sun

Can a full moon rise at midnight?

Earth

Sun

Full Moon

New Moon Half

Moon

No!

Half Moon

Sun

How can you tell the moon is close and the sun is far?

Earth

SunMoon

On the scale of the earth as a 10” globe, how far is the moon, sun, etc.?

Moon: 25 feet

Sun: 1.9 miles

Pluto: 73 miles

Alpha Centauri: 500,000 miles

Space Shuttle: 0.25 inch

What causes an eclipse?

Earth

Sun

Lunar Eclipse

Solar Eclipse

Why do we always see the same face of the moon?

MoonEarth

What causes the tides?

Earth

Sun

Moon

Moon

Where is the center-of-mass of the earth+moon?

Earth

Moon

R = 0.75Re

Where is the center-of-mass of the sun+earth?

Sun

Earth

R = 0.0006Rs

What does the orbit of the moon around the sun look like?

Sun

Moon