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TAMU ASTR 101 - What causes the seasons
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ASTR 101 1st Edition Lecture 4 Outline of Last Lecture I. The Universe,II. Scale of the solar system,III. Cosmic calendarOutline of Current Lecture –The Reason for SeasonsI. Clicker questions,II. What causes the seasons,III. 4 special points,IV. The orientation of Earth’s axis changes over time,V. 2.3- The moonCurrent LectureI. Clicker questions,a. On the (northern) spring equinox the Sun is moving: from the southern part of the celestial sphere to the northern part of the celestial sphere, on the celestial sphere, and on the ecliptic. b. The Sun is at its most Southern position on the celestial sphere on the northern hemisphere’s winter solstice.II. What causes the seasons,a. Depends on how Earth’s axis affects the directness of sunlightb. North and South poles barely intercept sunlight, that’s why they’re always coldc. The Sun is at its highest point in the summer, and at its lowest point in the winterd. Axis tilt—this is why the seasons change! It’s essential.III. 4 special points,a. Summer solstice (happens in June)b. Winter solstice (happens in December)c. 2 equinoxes (one in March and the other in September)d. The Sun rises and falls at various places on the meridian depending on the time ofyear.IV. The orientation of Earth’s axis changes over time,a. The axis isn’t fixed at its current position, but precesses (changes axis) very slowly—26,000 yearsb. The North Pole happens to be pointing to Polaris now, but it used to point to the star Vega. It won’t point to Polaris forever!These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.V. The moon!a. The orbital period of the moon is about 30 days (exactly 29.5) as referenced to the Sun. Different times are given when referenced to different objects. (27.3 days when referenced to the Earth)b. Phases of the moon—consequence of a 27.3 day orbit of Earth. It reflects the sunlight in different ways, appearing differently to the USi. Waxing= when the moon appears to be “growing”ii. Waning= when the moon appears to be “shrinking”c. Why do we only see one side of the moon?i. The moon’s rotation period and orbital period are the same, so we are only ever able to see one side. This is referred to as “synchronous rotation”.d. Eclipses= when Sun, Earth, and/or moon pass through another’s line/shadow. i. For an eclipse to occur…1. It has to be a new or full moon! New moon leads to a solar eclipse, and a full moon leads to a lunar eclipse. 2. The moon must be near orbit where it crosses its ecliptic planeii. Because of the moon’s shadow, we cannot see an eclipse everywhere on Earth at the same time. The moon’s shadow doesn’t cover the entire


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TAMU ASTR 101 - What causes the seasons

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