Obliquity and Seasons

1. Basic Definitions: Ecliptic
Ecliptic -
Plane of Earthʼs orbit around the sun. Sometimes also called
Ecliptic Plane.
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2. Basic Definitions: Inclination
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Inclination -
Angle between ecliptic and plane of planet (or satellite’s) orbit.

3. 9
Inclinations of Planets in the Inner Solar System

4. All Planets Are Near the Ecliptic
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Eris
Pluto
Ceres

5. 11
Saturn
Ecliptic From Earthʼs Surface
Venus
Jupiter
Mercury

6. Ecliptic From the Far Side of Moon
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7. Basic Definitions: Obliquity
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Obliquity - Tilt of planetʼs spin axis relative to plane of its orbit
around the sun.

8. Obliquity of the Planets
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Earthʼs obliquity is 23.5°

9. Obliquity of Other Planets
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Mercury - 0.1° Venus - 177° Earth - 23° Mars - 25°
Jupiter - 3° Saturn - 27° Uranus - 98° Neptune - 30°

10. Common Misconceptions about Seasons
#1) Many people think seasons on Earth are caused by
the change in the distance of Earth from the Sun.
In fact, Earth is closer to the sun in January than in July
(by about 5 million km).
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11. Earth’s Obliquity Causes Seasons
• Affects the length of day and angle of
sunlight.
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June 21
Sept 22
Dec 21
March 20

12. 25
Northern Summer Solstice
Longest Day

13. 28
The Equinoxes
12 Hour Day

14. Northern Winter Solstice
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Shortest Day

15. Angle of Sunlight Striking Earth
Angle depends on latitude and time of year
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16. Angle of Sunlight Striking Earth
Angle depends on latitude and time of year
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17. Earth’s Obliquity Causes Seasons
When northern hemisphere is tilted away from the sun the
resulting shorter days (longer nights) and greater angle of
sunlight lead to cooler temperatures (winter).
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18. THE END
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Precession - The natural tendency of all rotating objects to wobble.
The rotational axis of the Earth, and all planets, constantly wobbles.
For the Earth, one full precession takes approximately 26,000 years.