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Lecture 07: The Four Seasons
Why do we have different seasons? This lecture explores the
consequences of the tilt of the Earth's rotation axis relative to its
orbital plane combined with the apparent annual motions of the Sun
around the Ecliptic. The most important factor for determining whether
it is hot or cold at a given location at different times in the year is
"insolation": how much sunlight is spread out over the ground. This,
combined with the different length of the day throughout the year,
determines to total solar heating per day and so drives the general
weather. It has nothing to do with how far away we are from the Sun at
different times of the year. Finally, the direction of the Earth's
rotation axis slowly drifts westward, taking 26,000 years to go around
the sky. This "Precession of the Equinoxes" represents a tiny change
that is still measureable by pre-telescopic observations, and means that
at different epochs in human history there is a different North Pole
star, or none at all! Recorded 2007 Sep 27 in 1000 McPherson Lab on the
Columbus campus of The Ohio State University.
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By Richard Pogge
4.8
8080 ratings
Why do we have different seasons? This lecture explores the
consequences of the tilt of the Earth's rotation axis relative to its
orbital plane combined with the apparent annual motions of the Sun
around the Ecliptic. The most important factor for determining whether
it is hot or cold at a given location at different times in the year is
"insolation": how much sunlight is spread out over the ground. This,
combined with the different length of the day throughout the year,
determines to total solar heating per day and so drives the general
weather. It has nothing to do with how far away we are from the Sun at
different times of the year. Finally, the direction of the Earth's
rotation axis slowly drifts westward, taking 26,000 years to go around
the sky. This "Precession of the Equinoxes" represents a tiny change
that is still measureable by pre-telescopic observations, and means that
at different epochs in human history there is a different North Pole
star, or none at all! Recorded 2007 Sep 27 in 1000 McPherson Lab on the
Columbus campus of The Ohio State University.
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