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Office Hours Tue: 12:30 PM to 2:30 PM Wed: 9:00 AM to 10:30 AM & 12:00 PM to 2:00 PM Thr: 9:00 AM to 10:30 AM Course Syllabus can be found at: http://www.wx4sno.com/portfolio/BSU/Fall_2011/ This lecture will be posted AFTER class at: http://www.wx4sno.com/portfolio/BSU/Fall_2011/Lectures/ Lesson 10 Earth-Sun Relationships Hess, McKnight’s Physical Geography, 10 ed. 15-21 pp. Terms to Know Rotation: Earth completes one rotation every 24 hours giving us day and night. Terms, cont. Revolution: Earth completes one revolution around the sun every 365 ¼ days. Terms, cont. Revolution is not a perfect circle, more of an elliptic. When revolution brings earth closest to sun: perihelion When revolution takes earth furthest from sun: aphelion Point 1: Earth at aphelion Point 2: Earth at perihelion Point 3: Sun Perihelion and Aphelion, cont. Terms, cont. Ecliptic plane: This is the level, or plane, of Earth’s orbit around the sun…Earth’s orbital path. ◦ Astronomically, this is the primary plane referred to when discussing the revolution of other planets around the sun Terms, cont. Inclination: Relative to the ecliptic plane, Earth is tilted 23.5° from vertical at all times. Terms, cont. Polarity: Because Earth is always tilted 23.5°, it’s axis is always pointed in the same direction…towards the star Polaris. ◦ Because of this regular tilt, when the Earth revolves around the sun, the North pole is either tilted towards the sun (June) or tilted away from the sun (December) ◦ DO NOT confuse this with Earth’s magnetic field! Earth’s Equinoxes Equinox: Earth is positioned so that its is neither towards nor away from the sun…giving the entire planet equal amounts of day and night. ◦ Occurs twice each year, around March 20 and September 22. Earth’s Solstices Solstice: Earth is positioned where its tilt is either towards or away from the sun. ◦ Occurs twice a year, just like the Equinoxes, around June 21 and December 21. ◦ The direct rays from the sun hit the earth at 23.5°N on June 21, while the tangent rays hit the earth around 66.5°N and 66.5°S. Sun’s Rays during Equinoxes Sun’s Rays during Summer Solstice Sun’s Rays during Winter Solstice Video on Seasons http://www.youtube.com/watch?v=taHTA 7S_JGk Powers of ten: ◦ http://youtu.be/vRjGarICal4 ◦ http://youtu.be/0fKBhvDjuy0
