Models of the Universe Highlights of yesterday’s workshop Observations, virtually Todays’ workshop: compare two models E.J. Zita

Yesterday’s workshop Q1: Do you believe the Sun orbits the Earth, or Earth orbits the Sun? Q2: Why do you believe this? Q3: How can you know? Q4: Does it matter?

Why we believe Earth orbits Sun We were told it’s so: - by someone we trust - by a reliable or persuasive “authority” - by a textbook It’s “common knowledge,” “common sense”, or a “paradigm” Possible evidence? - seasons - phases of Venus and Mercury - retrograde motion of Mars - gravity – Sun is bigger - photos or videos from outside the solar system

Evidence: what do we experience? Gravity – why do things fall toward the center of the Earth? Because the Earth is the center of the universe? If the Sun is the center, why don’t things fall toward the Sun? Seasons – what do these tell us about the motion of Earth or Sun? Motion – what should it feel like if Earth were whizzing around the Sun?

Evidence: what do we see in the sky? Motion of Sun Motion of Stars Motion of planets Other evidence: gravity? seasons? Implications for Earth?

Virtual observations: We will use planetarium demonstrations to investigate a few of these phenomena. First, PREDICT WHICH of these you expect to see, if Earth orbits the Sun: - stellar parallax (relative motion of the fixed stars – yes or no?) - phases of Venus and Mercury (yes or no?) - retrograde motion of Mars (against the “fixed stars”) – yes or no?

Stellar Parallax - Q If Earth orbits the Sun, then we should see the “fixed stars” moving. Why? Model: - Hold out a finger as a “fixed star” - Let your right eye be Earth in January - Let your left eye be Earth in June

Stellar Parallax - Investigation EXPERIMENT: Blink one eye shut, then the other. REASON: If Earth moves (eyes), then the stars should appear to move (finger)

Stellar Parallax - OBSERVE We’ll use the planetarium to observe a constellation year after year, with some stars closer and other stars further away from Earth. If Earth orbits the Sun, what do you predict you will see in the stars? Watch the planetarium demo – do you see the stars change positions? What does this imply about the relative motion of Earth and Sun?

Stellar Parallax: last night’s N sky

Stellar Parallax: Sept & March

Phases of the Moon Why do we see these?

Phases of planets – Q1 IF we see phases of the Moon because the Moon goes around Earth, THEN, IF we saw phases of Venus and Mercury, - would that mean Venus and Mercury go around Earth? - would that mean Venus and Mercury and Earth go around Sun?

Phases of planets – Q2 IF we see phases of the Moon because the Moon goes around Earth, THEN, IF we DON’T see phases of Venus and Mercury, - would that mean Venus and Mercury don’t go around Earth? - would that mean Venus and Mercury and Earth go around Sun?

Phases of planets - OBSERVE Watch the planetarium demonstration. Can you see phases (e.g. a crescent shape) of Mercury or Venus? What could this tell you about the relative motion of Earth and Sun?

Phases of planets - VENUS

Retrograde motion of Mars Watch the planetarium demo. What is Mars doing? Why? What could this tell you about the relative motion of Earth and Sun?

We report, you decide You’ve seen the evidence. Now do the workshop. Which model fits the evidence best?

MODELS OF THE UNIVERSE workshop