SEASONS

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SEASONS

• Chapter 3

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WHAT IS THE REASON THAT WE HAVE SEASONS ON EARTH?
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SEASONS on EARTH

• Earths orbit is elliptical with a 3 variation
  in Earth-Sun distance
• Is this the cause of the seasons?

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EARTHS ELLIPTICAL ORBIT
Elliptical orbit cannot be reason for seasons as
if it were both hemispheres would have summer
when Earth closest to Sun. Earth at perihelion
in January - cold in North
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SEASONS on EARTH

• Seasons arise on Earth because the spin axis of
  Earth is TILTED with respect to the ECLIPTIC (the
  apparent path of the Sun on the Celestial Sphere,
  or the plane of Earths orbit around the Sun)

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SEASONS on EARTH

• Seasons arise on Earth because the spin axis of
  Earth is TILTED with respect to the ECLIPTIC (the
  apparent path of the Sun on the Celestial Sphere,
  or the plane of Earths orbit around the Sun)

• Seasons DO NOT arise because of changes in
  Earth-Sun distances. (Earth is closest to Sun
  early in January)

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SEASONS on EARTH

• Seasons arise on Earth because the spin axis of
  Earth is TILTED with respect to the ECLIPTIC (the
  apparent path of the Sun on the Celestial Sphere,
  or the plane of Earths orbit around the Sun)

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SEASONS on EARTH

• Seasons arise on Earth because the spin axis of
  Earth is TILTED with respect to the ECLIPTIC (the
  apparent path of the Sun on the Celestial Sphere,
  or the plane of Earths orbit around the Sun)

• Seasons DO NOT arise because of changes in
  Earth-Sun distances. (Earth is closest to Sun
  early in January)

9
SEASONS on EARTH

• Seasons arise on Earth because the spin axis of
  Earth is TILTED with respect to the ECLIPTIC (the
  apparent path of the Sun on the Celestial Sphere,
  or the plane of Earths orbit around the Sun)

10
SEASONS on EARTH

• Seasons arise on Earth because the spin axis of
  Earth is TILTED with respect to the ECLIPTIC (the
  apparent path of the Sun on the Celestial Sphere,
  or the plane of Earths orbit around the Sun)

• Seasons DO NOT arise because of changes in
  Earth-Sun distances. (Earth is closest to Sun
  early in January)

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VARIATION in the SUNS RAYS
If Sun high in sky (left) energy not spread out
significantly so warming effect of Sun is
strongest - summer. If Sun low in the sky (right)
energy spread out over larger area so that
warming effect smaller.
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FLASHCARD
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SEASONS on EARTH

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Sun's motion defines the seasons
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SEASONAL PATHS of the SUN
In summer Sun is far to North, so it rises North
of East and sets North of West. For northern
observer, it is above horizon for gt 12 hours. In
winter the Sun is far to the South so it rises
South of East and sets South of West. For
northern observer, it is above horizon lt 12
hours. At the equinoxes the Sun rises directly
East and sets directly West.
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SUMMER SOLSTICE
At summer solstice Sun overhead for those at 23
degrees latitude. All points North 67 degrees
see Sun for 24 hours. All points South 67
degrees never see Sun.
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WINTER SOLSTICE
At winter solstice Sun overhead for those at -23
degrees. All points North 67 degrees do not see
Sun at all. All points South 67 degrees see Sun
for 24 hours.
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FLASHCARD
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FLASHCARD
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FLASHCARD
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WINTER SOLSTICE
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FLASHCARD
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SUMMER SOLSTICE
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PLANETARY INCLINATIONS
Planet Inclination Equator to Orbit Seasons?
Mercury 0 degrees No
Venus 177.4 degrees Yes retrograde
Earth 23.5 degrees Yes
Mars 25.2 degrees Yes (like Earth)
Jupiter 3 degrees Yes
Saturn 27 degrees Yes
Uranus 97.9 degrees Yes (strange)
Neptune 29.6 degrees Yes
Pluto 122 degrees Yes retrograde
Most planets will experience seasons as their
axes are inclined to the ecliptic
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URANUS ORBIT
Seasons on Uranus are strange - its axis lies
almost in its orbital plane. North - 21 years of
summer (right) with the pole always facing
Sun. North - 21 years winter (left) with pole
always facing away from Sun.