Reasons for the Seasons True or False Seasons

Reasons for the Seasons

• True or False? Seasons are caused by the variation in distance between the Sun and the Earth. FALSE

• Note that summer and winter have nothing to do with how close Earth is to the Sun! • http: //www. cs. washington. edu/info/videos/asx/harvard. asx • http: //www. youtube. com/watch? v=FVz. TIMVK 4 PI • http: //www. youtube. com/watch? v=p 0 wk 4 q. G 2 m. Ig

The reasons for seasons • We have seasons on Earth… obliquity because of the _______ of the ecliptic. tilt of the spin axis -specifically, the ________ to the ecliptic

Apparent motion: Earth’s orbit: Seasons • Earth’s axis is tipped by 23. 5 o

Tilt of the earth on its axis. • The earth is tilted 23. 5º from perpendicular to the plane of the ecliptic.

Apparent motion: Earth’s orbit: Seasons • When your hemisphere is tipped ____ towards the Sun, it is ____ summer for you • When your hemisphere is tipped _____ away from the Sun, it is _______ winter for you

• The tilt of the Earth’s spin axis produces a geometrical heating effect – Sun near Summer Solstice position • long days with Sun ______ high in the sky • hence _____ warm days – Sun near Winter Solstice position • ______ short days with Sun low in the sky • hence _____ cold days Note: this is a northern hemisphere view point of the seasons

The Earth is curved and this causes differing angles of incidence.

Seasons Clip

Seasons Animation

Seasons Animation

Intensity of incoming solar radiation (insolation) is related to angle of incidence. Higher angles = higher intensity. _______________

SOLSTICES SUMMER, JUNE 21 WINTER, DECEMBER 21 Where are the overhead rays of the sun on these days? o. N N. Hemisphere 23. 5 ________ o. S S. Hemisphere 23. 5 ________

EQUINOXES VERNAL, MARCH 21 AUTUMNAL, SEPTEMBER 21 _______ Equator

NCP To Sun at Summer Solstice To Sun at Equinoxes 23. 5 o (celestial equator) 23. 5 o Spin axis T of Can. T of Cap. Earth To Sun at Winter Solstice

Annual Changes in Daylength

Important points to understand: NOT due to variation in the • Seasons are _____ Earth-Sun distance. Earth’s spin • We have seasons because _______________________ axis is inclined to the plane of Earth’s orbit ________ around the Sun. • This tilt (or obliquity) causes variation in the amount of daily sunshine any particular location receives throughout the course of a year. more energy = warmer • More sunshine = ______ time of year • Less sunshine = less energy = cooler _____ time of year

Important points to understand: reversed in northern and • Seasons are _____ southern hemispheres. • Regions near the pole can experience “midnight sun” near summer solstice; days without sunrise near winter solstice. • At intermediate latitudes (like ours), the Sun climbs higher in the sky in summer, lower in winter.

Seasons Video http: //www. youtube. com/watch? v=Yy. Kv XX 8 i. GE 4

www. glendale. edu/geo/reed_physical/ 101%20 Powerpoint/c_seasons_and_time. ppt