Revolution Seasons

8/2/2019 Revolution Seasons

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Earths RevolutionSeasons and Retrograde Motion of Planets


2/18

Earths Revolution

Revolution is the motion of a body that

travels around another body in space.

Earth takes 365 days to revolve around

the sun. Earth does not revolve in a perfect circle.


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Aphelion and Perihelion


4/18

Tilt of Earths Spin Axis

23.5o tilt

The Earths spin axis is tilted by 23.5 degrees off

vertical with respect to the ecliptic plane

(plane of the Earths orbit around the sun)


5/18

Amount of Light Changes in the angle at which the suns rays

strike Earths surface cause the seasons. When the Northern Hemisphere is tilted away

from the sun there is less direct sunlight and less

total daylight which leads to coolertemperatures.

When the Northern Hemisphere is tilted towardthe sun there is more direct sunlight and more

total daylight which leads to warmertemperatures.


6/18

The Seasons


7/18

sunlight

sunlight

Summer Solstice June 21 or 22

equator

antarctic

circle

arctic

circle

tropic of

Cancer


8/18

sunlight

sunlight

Winter Solstice December 21 or 22

equator

antarctic

circle

arctic

circle

tropic ofCapricorn

tropic of

Cancer


9/18

sunlight

sunlight

Vernal Equinox March 21 or 22

equator

antarcticcircle

arctic

circle

tropic of

Cancer

tropic of

Capricorn


10/18

sunlight

sunlight

Autumnal Equinox September 21 or 22

equator

antarcticcircle

arctic

circle

tropic of

Cancer

tropic of

Capricorn


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Seasons


12/18

Other Seasonal Extremes

The sun never rises for observers north of

the arctic circle on the day of the winter

solstice.

The sun never sets for observers north of

the arctic circle on the day of the summer

solstice.

This is opposite for the antarctic circle.


13/18

Tilt of Earths Spin Axis

S

W

Ewinter

solsticesummer

solsticeequinox

The sun rises on the east point and sets on the west point on the days of the equinoxes, giving

equal periods of day and night.

The sun is in the sky for the longest duration on the summer solstice and illuminates

the northern hemisphere most directly.


14/18

Temperature Effect

Summer days are longer and the sun is more

intense (due to the more direct illumination angle).

Thus summer is hotter than winter.

If the Earths spin axis were not tilted by

some angle, we would have no seasons.

There is a lag of the seasons when comparing

the dates of the solstices with the actual

extremes in temperature because it takes timeto heat up the oceans and atmosphere at the

onset of summer and to cool them off at the

onset of winter.


15/18

Motions of the Wanderers The Planets

The night sky facing south

WestEast

normal direct (eastward) motion retrograde motion

Mars


16/18

Retrograde Motion of Planets The apparent backward motion of other planets

as Earth revolves around the sun. Early Models of the Solar System:

Aristotle: Earth centered geocentric

Copernicus: Sun centered heliocentric

Aristotles model could not explain retrograde

motion. Galileo then observed moons of Jupiter

going around Jupiter which supportedCopernicus sun centered theory.


17/18

Aristotles View


18/18

Copernicus View

Revolution Seasons

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