Seasons

Ch 22.2 Solar Energy and the Atmosphere page 555

The Orbit of the Earth

closest point to the Sun --perihelion: – distance is about 147 millions of km. – We are closest to the Sun in January.

farthest point to the Sun --aphelion: – the distance Sun-Earth is about 152 millions of km. – We are farthest from the Sun in July.

During the equinoxes, the distance Sun-Earth is about 149.5 millions of km.

So . . . distance is not the cause of the seasons

So WHAT IS???

The earth has a 23.5° tilt!

tilt of Earth and other planets originates from collisions with large bodies during the formation of the planets in the solar system

Solar Energy p 559

The important thing is that the angle at which the sunlight hits the earth

See the two equal amounts of sunlight

The pink box receives the same total amount but it is spread out over a larger area

So it receives a smaller portion of the heat

Angle of Incidence

The Seasons

Because of the Earth's tilt, on June 21st, the sun is directly overhead on the tropic of Cancer in the northern hemisphere and on December 21st, the sun is directly overhead on the tropic of Capricorn in the southern hemisphere: – These are called solstices

In March and September 21st, the sun rays strike the equator most directly: the Earth is illuminated from pole to pole: this is the equinox.

Equator, Tropic of Cancer, Tropic of Capricorn, Arctic Circle

Equator

The tropic of Cancer– located 23.5° north of the Equator.

– On June 21st, the sun is directly overhead the tropic of Cancer at noon

The tropic of Capricorn– located 23.5° south of the Equator.

– On December 21st, the sun is directly overhead the tropic of Capricorn at noon

The Arctic Circle/Antarctic– located 23.5° south of the North Pole/North of South Pole

Terrestrial Radiation

The sun sends primarily short-wave radiation

This is absorbed by earth’s surface and reradiated as long wave IR rays

The lower atmosphere is mainly warmed by this terrestrial radiation

The Greenhouse Effect

Greenhouse gases

Carbon dioxide is one of the greenhouse gases.

carbon dioxide molecule can absorb infrared radiation and the molecule starts to vibrate.

Eventually, the vibrating molecule will emit the radiation again, and it will likely be absorbed by yet another greenhouse gas molecule.

This cycle serves to keep the heat near the surface, insulating the surface from the cold of space.

What would happen if the Earth's axis was not tilted?

If the axis of the Earth was not tilted, the Earth would receive the same illumination all year long!

Try these multiple choice ?’s

The imaginary pole that runs through the center of Earth is

called the _____. axis

equator

South Pole

North Pole

The four seasons are a result of the tilt of Earth's axis and Earth's ___.  

loss of internal heat

orbit around the sun

distance from the sun

rotation about its own axis

The northern hemisphere is tilted toward the sun during

the month of _____. January April

July

October

When the northern hemisphere is in the middle of winter, the southern hemisphere is in the middle of ____.

spring

summer

fall

winter

Between December and June,

the tilt of Earth's axis _____.

shifts by about 25 degrees

shifts by about 45 degrees

shifts unpredictably

does not change

Which of these is a major greenhouse gas?

CaCO3

H2O

CO2

NH3

The Atmosphere and Solar Radiation

The atmosphere affects radiation in several ways

Upper atmosphere absorbs almost all radiation shorter than visible light

N2 and O2 in thermosphere and mesophere absorb the x-rays, gamma rays, and UV rays

Most of the rays that reach the lower atmosphere, like visible and infrared, have longer wavelengths

Most of the incoming infrared is absorbed by carbon dioxide

Does page 556 Fig 2 agree with this graphic?

Albedo-See page 557