Seasons
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Transcript of Seasons
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