Unit 2 Water and Weather - Spokane Public Schools

Revolution and Earth’s seasonsWhy does Earthhave seasons?Earth is tiltedThe diagram below shows Earth at four different places in itsrevolution around the Sun. Why is it warmer in summer andcooler in winter in the northern hemisphere? In other words,why do seasons occur?One guess might be that Earth is closer to the Sun duringsummer. But this isn’t the correct answer. Earth has seasonsbecause it is tilted on its axis. During our summer, the northernhemisphere receives sunlight that is more direct than it is in thewinter, and in summer there are more hours of daylight. Thismeans we have warmer temperatures in summer than we do inwinter.Earth’s axisEarth rotates about an imaginaryaxis that goes through its center.This axis is drawn on the imagesof Earth in the diagram on thispage. The diagram shows thatEarth is tilted at 23.5° as itrevolves around the Sun.The axis connects the North Poleand the South Pole. The north endof the axis points toward the NorthStar throughout the year.Make your own sketch of thediagram at the left. Based ontoday’s date, indicate on yourdiagram where Earth is on its patharound the Sun.114UNIT 2 WATER AND WEATHER