Reasons for the SeasonsChapter 17.1

Figure 1.1Figure 1.1

Nearly Nearly 150 million kilometers150 million kilometers separate separate the sun and Earth, yet solar radiation the sun and Earth, yet solar radiation drives Earth's weather.drives Earth's weather.

Does the distance from the Sun make the Seasons?

• NO• The Earth is actually farther away from the

Sun when we have our Summer.

Perihelion- Earth is closer to the SunJanuary 3rd

Aphelion- Earth is farthest from the SunJuly 6th

Reason for the Seasons1. The Earth’s tilt causes the seasons• It is tilted at 23.5 degrees

• The angle of the sun’s radiation (Insolation) hitting the Earth impacts the climate or temperature.

If the tilt were the only factor, then every location on Earth would have one season

and it would never change.

2. Earth’s Revolution • Causes the Suns rays to strike at different locations

as the Earth orbits the Sun.

When northern hemisphere is facing the sun:•Summer Solstice (June 21st or 22nd )

SUMMER SOLSTICE• Most direct rays over Northern Hemisphere• •Striking at Tropic of Cancer 23.5° N.• Light = 15 hours (about 14.27 (NC) Dark = 9 hours

Antarctica is completely dark for 24 hours and the Arctic is completely light for 24 hours!!!

Fall Equinox (September 22 or 23)

• EQUAL amounts of daylight and darkness everywhere.• Direct rays over Equator:• Light = 12 hours Dark = 12 hours

• Winter Solstice - December 21-22• SHORTEST DAY !!!• Most direct rays over Southern hemisphere

•Striking at Tropic of Capricorn 23.5°S• Light = 9 hours Dark = 15 hours

Spring Equinox (March 21 or 22)

• EQUAL amounts of daylight and darkness everywhere.• Direct rays over Equator:• Light = 12 hours Dark = 12 hours

The Southern Hemisphere has opposite Seasons than us . . . WHY?

Light - Year– The unit used to measure

stellar (star) distance. • The distance that light travels

in one year.

– 9.5 x 1012 kilometers a year.– 180,000 miles per second.