Question 7: When Galileo first used a telescope for astronomical purposes, one o
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Question 7: When Galileo first used a telescope for astronomical purposes, one of the first things he observed was Venus. His observations of the phases of Venus constituted one of the strongest proofs that Copernicus' heliocentric (Sun-centered) model of the solar system was right, and that the geocentric (Earth-centered) model was wrong. This question will help you see why.. (a.) Consider a geocentric model where both Venus and the Sun orbit the Earth, where Venus is closer to the Earth than the Sun is. (Ancient astronomers knew Venus was closer than the Sun to Earth because they occasionally saw Venus transit the Sun.) List the times of day (dawn, noon, dusk or midnight) when you would you see Venus in a new, first quarter, full and third quarter phase crossing your local meridian if the geocentric model were right. (b.) Now do the same for a model where both Venus and Earth orbit the Sun (a "heliocentric model"). (c.) Explain how this analy- sis proves the heliocentric model. (Hint: Check your notes to find the mazimum angular separation of Venus and the Sun!)Explanation / Answer
a)
According to the grocentric model, Earth is at the center and all other planets and stars orbit around it. The various positions of Venus according to this model as seen from the Earth will be:
full -> dawn
first quarter --> noon
new --> dusk
third quarter --> midnight
b. According to heliocentric model, Sun is at the center and all the planets revolve around it. Now both Venus and Earth move around the Sun.
third quadrant --> dawn
full --> noon
first quadrant --> dusk
new --> midnight
c. According to this the full venus will never be visible from the Earth, due it being covered by the Sun which is actually true. Hence heliocentric model is true while geocentric model is not.
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