reasons for the seasons subject: science topic: astronomy
TRANSCRIPT
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Reasons for the Seasons
Subject: ScienceTopic: Astronomy
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ASTRONOMY
Astronomy ~ the study of space including:.
1. stars
2. planets
3. other objects
AND their origins
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ROTATION
The spinning around a central point or axis.
Causes ~ day & night
Rotates from West to East
1 Rotation = 1 DayEx: Earth rotates in
24 hr.
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REVOLUTIONTo travel in a circular path around another object.
1 Revolution = 1 year
ORBIT ~ the path an object takes as it revolves around something.
Earth orbits the sun in 365 ¼ days
Earth’s orbit nearly a perfect circle – a slight ellipse
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EARTH’S TILTED AXIS
Tilted at 23.5° angle from the vertical
Axis tilted toward the sun in northern hemisphere during summer.
a. longer periods of daylight
b. physically farthest from sun
(about 152 million km)
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EARTH’S TILTED AXIS
Tilted away from sun in northern hemisphere during winter.
a. shorter periods of daylight
b. physically closest to the sun in winter
(about 147 million km)
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EARTH’S SEASONS
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The Real Reasons for the Seasons
Seasons: Spring, Summer, Autumn & Winter
Both Earth’s tilted axis AND its revolution around the sun cause the seasons.
Distance from the sun is NOT the reason for the seasons.
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How Sunlight Strikes the Earth
1. At equator sunlight strikes earth directly. It is usually around 80-88 degrees all year! Difference in temperature from winter to summer is only 1 degree.
2. Closer to the poles sunlight
strikes earth at an angle
a. near poles sunlight spreads out over
larger area
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EQUINOXMeans ~ equal nights
a. length of day & night about equal
Noon sun is directly overhead at equator
Earth’s tilt not toward or away from the sun. Zero tilt.
Vernal Equinox ~ spring begins in N. hemisphere
Autumnal Equinox ~ fall begins in N. hemisphere
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SOLSTICENoon sun is overhead at
23.5° N (June) 23.5° S (December)
Summer Solstice – longest day (≈ June 21)
1st day of summer
Sun at it’s highest point
Winter Solstice – shortest day (≈ Dec. 21)
1st day of winter
Sun at it’s lowest point
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EQUINOX AND SOLSTICE
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Interesting Facts
Utah has the greatest number of day light hours in the summer.
The sun’s rays strike the earth the farthest north and the farthest south during the summer and winter solstices.
If you watched the night sky for several hours, the stars would appear to be moving around the North Star, however the stars aren’t moving.