Mastering Astronomy assignment 3 notes + answers

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Astronomy & Astrophysics
Stefan Mochnacki

Many people guess that seasons are caused by variations in Earths distance from the Sun, but if that were the case, wed expect it to be warmest (summer) when Earth is closest to the Sun. As you can see in the rankings, Earth is actually farthest from the Sun when it is summer in the Northern Hemisphere. We conclude that variations in the Earth-Sun distance from are not the major cause of our seasons The fact that the two hemispheres have opposite seasons is further proof that the seasons are not caused by Earths varying distance from the Sun. Keep in mind that Earth is so small in size (diameter 12,800 km) compared to its distance from the Sun (about 150 million km) that there is no significant difference in the distances of the two hemispheres from the Sun; therefore, if the seasons were caused by Earths varying distance from the Sun, the entire Earth would have summer at the same time. As youve already seen in Parts A and B, seasons on Earth are not affected by the variation in Earths orbital distance over the course of each year. This is probably not too surprising when you realize that Earth always stays within about 3 percent of its average distance from the Sun. Other factors are much more important in creating the seasons. The tilt of Earths axis causes different portions of the Earth to receive more or less direct sunlight at different times of year. Without axis tilt, we would not have seasons on Earth. Seasons on other planets occur for the same reason, which is why planets with axis tilts (such as Mars and Saturn) have seasons and planets with very little axis tilt (such Jupiter or the upside-down axis of Venus) do not. Notice that the figure with the most daylight shows that it is summer in Florida (because t
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