Chapter 4

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Middle Tennessee State University *

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1010

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Astronomy

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Apr 3, 2024

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docx

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2

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Chapter 4 1) Darw and label a diagram of the western horizon from northwest to southwest and label the setting points of the sun at the solstices and equinoxes for a person in the northern hemisphere. 2) If you lived on mars, which planets would exhibit retrograde motion like that observed from mars from earth? Which would never be visible as Crecent phases? The retrograde motion would be for the outer planets like Jupiter and the crescent phases for the inner planets like earth, Venus, and mercury. 3) How long does it take for one retrograde cycle of mars as viewed from earth, and in which direction is the retrograde motion? What fraction of Mars's orbit around the sun is the duration of retrograde motion as viewed from earth? Mars moves westward every 2.14 years finishing one retrograde cycle. Mars is in retrograde for roughly 10% of its orbit around the sun. (70/687 =0.1 =10%) 4) If a planet has an average distance from the sun of 2.0 au, what is its orbital period? p^2=2^3 The orbital period is 2.8 years 5) If a space probe is sent into an orbit around the sun that brings it as close as 0.4 au and as far away as 5.4 au, is the orbit a circle or an ellipse? What will be its orbital period? The orbit is elliptical. A=0.4 AU +5.4 AU/2 =2.9 AU, then p^2=2.9^3 = 4.9 meaning that the orbital period of the space probe is 4.9 years.
6) Uranus orbits the sun with a period of 84 years. What is its average distance from the sun? a^3 = 84.0^2 = 19.2 AU Uranus’s average distance from the sun is 19.2 AU 7) An object takes 29.5 years to orbit the sun. What is the average distance from the sun? a^3 = 29.5^2 = 9.6 AU from the sun 8) One planet is three times farther from the sun than another. Will the farther planet take more, less, or the same amount of time to orbit the sun? Will the closer planet orbit slower, faster, or the same speed? How much longer will the farther planet take to orbit than the closer planet? If the closer planet is located at 10 AU, how far is the father planet and what are the two planets' names? The farther planet will take about 5.2 times more time to orbit around the sun and the closer planet will orbit faster 9) Galileo's telescope showed him that Venus has a large angular diameter (61 arc seconds) when it is a crescent and a small angular diameter (10 arc seconds) when it is nearly full. Use the small-angle formula to find the ratio of its maximum to minimum distance from Earth. Is this ratio compatible with the Ptolemaic universe shown in Figure 3b of the Chapter 4 Concept Art: An Ancient Model of the Universe? 10) Which is the phase of Venus when it is the closest? Which when farthest? How do you know? The crescent phase when it is the closest, the sun is behind Venus. We know this because the full phase is when it is the farthest, so the sun is between earth and Venus. 11) Galileo’s telescopes were not of high quality by modern standards. He was able to see the moons of Jupiter, but he never reported seeing features on Mars. Use the small-angle formula to find the angular diameter of Mars when it is closest to Earth. How does that compare with the maximum angular diameter of Jupiter? The angular size of mars is smaller than the angular size of Jupiter.
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