PGCC PSC 121 Gage The Earth and Sun Shedding Some Light on the System.

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The Earth and SunThe Earth and Sun

Shedding Some Light on the Shedding Some Light on the SystemSystem

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Earth’s Rotation…Earth’s Rotation…

Earth’s rotation on its axis generates Earth’s rotation on its axis generates periods of daylight and night.periods of daylight and night.

http://www.onr.navy.mil/focus/http://www.onr.navy.mil/focus/spacesciences/observingsky/spacesciences/observingsky/motion1.htmmotion1.htm

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Earth’s Rotation…Earth’s Rotation…

The amount of daylight/nighttime is also The amount of daylight/nighttime is also determined by the amount of Earth’s tilt. determined by the amount of Earth’s tilt. The Earth’s axis is tilted 23.5The Earth’s axis is tilted 23.5oo from the from the plane of the Earth’s orbit around the Sun.plane of the Earth’s orbit around the Sun.

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Earth’s Rotation…Earth’s Rotation…

The amount of daylight/nighttime is also The amount of daylight/nighttime is also determined by the amount of Earth’s tilt. determined by the amount of Earth’s tilt. The Earth’s axis is tilted 23.5The Earth’s axis is tilted 23.5oo from the from the plane of the Earth’s orbit around the Sun.plane of the Earth’s orbit around the Sun.

http://janus.astro.umd.edu/astro/seasons/http://janus.astro.umd.edu/astro/seasons/

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Earth’s Revolution…Earth’s Revolution…

The motion of the The motion of the Earth in its orbit Earth in its orbit around the Sun is around the Sun is an an ellipseellipse, not a , not a circle. That means circle. That means that at some points that at some points in the orbit the in the orbit the Earth is closer to Earth is closer to the Sun than at the Sun than at others. others.

Circle Ellipse

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Earth’s Revolution…Earth’s Revolution…When the Earth is closest it is at When the Earth is closest it is at perihelionperihelion. .

When it is farthest, it is at When it is farthest, it is at aphelionaphelion. The . The difference in distance is about 3.5%...not difference in distance is about 3.5%...not enough to account for the seasonal enough to account for the seasonal changes!changes!

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Earth’s Revolution…Earth’s Revolution…So what causes the daily and seasonal So what causes the daily and seasonal

changes?changes?

Earth’s curvature Earth’s curvature And its tilt !And its tilt !

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Earth’s Revolution…Earth’s Revolution…

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Earth’s Revolution…Earth’s Revolution…

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Earth’s revolutionEarth’s revolution

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Earth’s RevolutionEarth’s Revolution

http://www.cs.sbcc.cc.ca.us/~physics/flash/LengthofDay.swf

Since Earth’s tilt always points in the same direction, at a given point on the Earth the rays change in directness and duration.

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Earth’s RevolutionEarth’s Revolution

Since Earth’s tilt always points in the same direction, points on the Earth will experience seasonal changes.

http://www.astro.uiuc.edu/projects/data/Seasons/seasons.html