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1.15 Astro 1 - Question 3 What causes seasons What makes...

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Astro 1 Section 1 Professor Brandt Friday January 15th 1999 Announcements: Lecture notes: Four Basic Important Questions Why day and night? What causes the seasons? Why different stars in summer and winter? What makes phases of moon? Four Basic Important Facts Earth orbits sun in 1 yr Earth rotates in 1 day Rotation axis tilted from plane of orbit by 23.5 degrees Moon orbits Earth in about 27.3 days Title of today's lecture is Darkness and Light Winter and Summer discuss and answer 5 basic but important questions To answer them we will frequently use 4 important facts Question 1 - Why day and night? Circumpolar rotation = the stars appear to move around a particular star called the North Star (Polaris) during course of night Point out Big Dipper and pointer stars Little Dipper and Polaris Arcturus - students name it Takes 24 hours - 24 hour rotation of Earth What would sky at North Pole look like - pointer stars still point to Polaris
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Unformatted text preview: Question 3 - What causes seasons? What makes days longer in summer than in winter? Use fact #3 - rotation axis is tilted from orbital plane by 23.5 degrees Earth's rotation vector points towards Polaris and is fixed there Changes angle at which sun's rays strikej different parts of Earth's surface Extreme of North Pole and South Pole In far North during summer doesn't get dark at all. Seasons produced by combination of tilt of Earth's axis and the revolution about the sun. No tilt = no seasons Summer solstice is June 21 = longest daylight of year in far Northern hemisphere Winter solstice = December 21 = shortest daylight of year in far Southern hemisphere Fall and spring equinoxes Spring equinox = March 21 Autumn equinox = September 23 Why different stars in summer and winter? Can't see stars located behind sun. Phases of Moon not Earth blocking sunlight from Moon - this only happens during eclipses...
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