PHY 118 final study guide -chapter 2

# PHY 118 final study guide -chapter 2 - PHY 118 Final Study...

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PHY 118 Final Study Guide: Chapter 2 I. Earth-Sun Relationships: a. Unequal heating of Earth by the sun creates winds and drives ocean currents, resulting in weather b. Earth’s Rotation – Spinning of earth about its axis that produces the daily cycle of light and dark c. Earth’s Revolution – Movement in orbit around the Sun d. Distance between earth and sun averages about 150,000,000 km (93,000,000 mi); Earth’s orbit is not perfectly circular so distance varies i. Perihelion – Occurs each year on January 3 rd , Earth is closest to the sun at a distance of 147,000,000 km (91,500,000 mi) ii. Aphelion Occurs each year on July 4 th , Earth is farthest from Sun at a distance of 152,100,000 km (94,500,000 mi) e. Sun Angles: (Most important factor in the seasonal changes) i. When the Sun is directly overhead its rays strike earth at a 90 degree angle and solar rays are most concentrated ii. One Atmosphere (as a unit) – The distance of the solar rays path when the striking the Earth at a 90 degree angle; shortest path between Sun and Earth iii. The lower the sun angle, the longer the path it must travel to reach the surface and the greater the chance the solar rays will be absorbed, reflected, or scattered by the atmosphere iv. Equation for Sun Angles: 1. 90 - (Latitude of location – Declination) 2. 90 – (Distance between the latitude of the location you want to know about and the latitude being struck by vertical rays) v. Only Honolulu, Hawaii (@ 21 degrees north latitude) experiences 2 90 degree sun angles a year f. Plane of Ecliptic – The plane of Earth’s orbit around the Sun g. Inclination of the Axis – The 23.5 degree tilt of Earth’s axis relative to the Sun i. Without this tilt, there would be no seasons ii. Season Dates: 1. Spring Equinox – March 21, 22 a. Vertical rays strike 0 degrees latitude (equator) b. Axis is tilted neither towards nor away from Sun 2. Summer Solstice – June 21, 22 a. Axis in N. hemisphere is tilted 23.5 degrees toward Sun b. Tropic of Cancer – located at 23.5 degrees north latitude, on this day vertical rays strike here c. Longest day in N. hemisphere, the more north a location the more daylight it gets 3.

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