1 Why do we have seasons? Jeff Gawrych Met 10. 2

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Why do we have seasons?

Jeff Gawrych

Met 10

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DefinitionsDefinitionsInsolation –

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Obliquity –_____________________________________

Solstice –_______________________________________________________________________________

Equinox ______________________________________________________________________

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Distance from the Sun

NOT the main reason we have seasons

However, it is a factor…Depends on eccentricity

• Def.

Presence of an atmosphere

Earth is closest to sun in _________

Earth is furthest from sun in _________

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147 million kilometers147 million kilometers 152 million kilometers152 million kilometers

Guess the monthsGuess the months

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What influences incoming What influences incoming solar energy?solar energy?

The Sun’s angle of incidence:A.k.a Overhead angle

High Angle

Low Angle

Length of time the Sun shines each day:Long days can be deceiving…

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Sun angleSun angle

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Sun angleSun angle

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What influences incoming What influences incoming solar energy?solar energy?

The Sun’s angle of incidence:Lower sun angle,

Higher sun angle,

Length of time the Sun shines each day:Summer season,

Winter season,

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This says at that the NP get more This says at that the NP get more insolation than the equator??insolation than the equator??

Why? Why? AttenuationAttenuation

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What month do you think this graph represents?What month do you think this graph represents?a) December b) March c) June d) Septembera) December b) March c) June d) September

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On June 21st, at what latitude is the sun directly overhead at noon?

On September 22nd, at what latitude is the sun directly overhead at noon?

How many hours of daylight are present at the South Pole on February 20th?

Where would you expect to have longer days; 45 ° N on June 21st or 50°S on Dec 21st?

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Further points to considerFurther points to consider

You may be able to tell which was north is by looking at local vegetation.

Why?

The southern hemisphere (SH) receives slightly more solar radiation than the northern hemisphere (NH), during summer.

Why isn’t the SH summer warmer than the NH summer?