1. The Reasons for Seasons
Copyright 2005 by the Rector and Visitors of the University of Virginia
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The Seasons

2. Rotation vs. Revolution
Rotation is the spin of an object about its axis.
The Earth rotates once a day (once every 24 hours).
Revolution is the orbit of one object around another.
The Earth revolves around the Sun every days.
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3. Tilt of the Earth’s Axis
The axis around which the Earth rotates is tilted by 23.5 degrees.
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5. Do this… Complete 1-4: Checking Concepts on Page 327.
Complete 5-8: Thinking Critically on the
Same page.
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6. Time Zones The Continental U.S. has four time zones. Eastern Standard
Central standard
Mountain standard
Pacific Standard
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7. Time Zones
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8. Solar Noon: time of day when the sun is highest in the sky.
Time Zones
Solar Noon: time of day when the sun is highest in the sky.
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9. International Date Line
The International Date Line line was established in the middle of the Pacific Ocean.
As you go from east to west, you gain a day as you cross the line.
As you go from west to east, you lose a day as you cross the line.
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10. Daylight Saving Time
During the late spring, and early fall, we set our clocks ahead/back to gain or lose an hour.
This change in time is called Daylight Saving Time.
spring ahead, fall back.
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11. Do This:
Complete Checking concepts: 1-5 and Thinking Critically: 6 – 10.
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12. Equinoxes and Solstices
The Vernal (Spring) Equinox (about March 21): When night and day are the same length.
The Summer Solstice (about June 21): The location where the Sun is at its highest in the sky. Longest day of the year.
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13. Equinoxes and Solstices
The Autumnal (Fall) Equinox (about September 21): When day and night are the same length.
The Winter Solstice (about December 21): The location where the Sun is at its lowest point in the sky. Shortest Day of year.
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15. Tropics
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16. Seasons Misconception
Perihelion when earth is at its closest point to the sun.
Aphelion when earth is at it farthest point from the sun.
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17. Seasons Misconception
While it is winter in the Northern hemisphere it is summer in the Southern hemisphere. If the seasons were due to our distance from the Sun both hemispheres would have the same seasons at the same time.
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18. Orbit of the Earth
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19. The Length of the Day
A day is defined as the time that it takes the Earth to rotate on its axis. Duh!
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20. Length of a Year
It takes Earth one year to orbit the Sun That’s days to you. Duh!
A sidereal year is the length of time it takes for the Earth to return to the same position
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