Why Do We Have Seasons?

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Why Do We Have Seasons?
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Thats easy!
The Earth is closer to the Sun in Summer.
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Thats easy!
The Earth is farther from the Sun in Winter.
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Thats easy!
Everybody knows that!
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Wrong!
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Didja know
The Earth is closest to the Sun in Winter
farthest in Summer.
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Heres the Sun thru the Year.
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You can actually see the apparent size of the Sun
change.
Larger (closer) Winter Smaller (farther) -
Summer
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If distance from the Sun isnt responsible, what
is?
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Look at Earth
The Earth is not straight up and down.
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The Earths axis is titled 23.5.
Source Dr. Mike Eracleous website, Penn State
University
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Why?
4.5 billion years ago, Earth was hit by an object
the size of Mars.
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Why?
This formed the Moon and knocked the Earth on its
side 23.5.
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Why?
It also resulted in the Earth tilting 23.5.
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So why do we have seasons?
Its the tilt, baby!
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Fact The Earth revolves around the Sun (click
the picture).
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Combine the Earths tilt and its revolution
around the Sun, you get seasons!
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As the Earth revolves around the Sun, different
parts of the Earth tilt towards the Sun.
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Summer
Earth tilts towards the Sun.
Source Virtual Solar System http//inkido.indian
a.edu/a100/projecthelp.html
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Winter
Earth tilts away from the Sun.
Source Virtual Solar System http//inkido.indian
a.edu/a100/projecthelp.html
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Autumn/Spring
Earth does not tilt towards or away from the Sun.
Source National Schools Observatory http//www.
schoolsobservatory.org.uk/news/arch/sky0906.shtml
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The tilt affects the Earth in two important ways.
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The Earth receives either direct or indirect
sunlight (heat energy).
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Direct sunlight (heat energy) is received in the
Summer.
Indirect sunlight (heat energy) is received in
the Winter.
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Look at this diagram.
Source ASD Planetarium http//www.astronomy.org/
programs/seasons/index.html
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Look at the diagrams.
Warm covers small area.
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Look at the diagrams.
Cool same amount of sunlight (heat energy)
covers larger area.
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Key Season Dates
First day of Summer around June 21st.
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Key Season Dates
June 21st also has the most daylight hours of any
day in the year.
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Key Season Dates
June 21st The Summer Solstice (the Sun is
farthest north in the sky).
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Why is summer sometimes called the dog days of
summer? Click below to find out!
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Key Season Dates
First day of Autumn around September 21st.
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Key Season Dates
September 21st Autumnal Equinox.
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Key Season Dates
Equinox equal nights.
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Key Season Dates
Daylight nighttime both last 12 hours.
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Key Season Dates
First day of Winter around December 21st.
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Key Season Dates
December 21st also has the fewest daylight hours
of any day in the year.
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Key Season Dates
December 21st The Winter Solstice (the Sun is
farthest south in the sky).
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Key Season Dates
First day of Spring around March 21st.
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Key Season Dates
March 21st Vernal Equinox.
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Can you really balance an egg only on the
equinox? Click on the egg to see!
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The Sun appears to move thru the sky during the
year.
This is called an analema.
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Summer
Autumn/Spring
Winter
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North
South
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The second way the tilt affects the seasons is
the number of daylight hours.
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The clip on the next slide shows how daylight
changes thru the year.
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When the Earth is tilted towards the Sun
(summer), more of the Northern Hemisphere is in
daylight.
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Source http//www.astro.psu.edu/mce/A001/lect03
.html
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At the North Pole, there is 24 hours of sunlight
in the summer.
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As you move south, the daylight hours decrease
until you reach the equator.
Daylight hours last 12 hours.
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Continue moving south and daylight hours continue
to decrease
When you reach the South Pole, nights last 24
hours (its winter).
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Source http//www.personal.psu.edu/faculty/j/e/j
ea4/earth/climate2.html
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At the North Pole, night lasts 24 hours in the
winter.
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As you move south, the daylight hours increase
until you reach the equator.
Daylight hours last 12 hours.
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Continue moving south and daylight hours continue
to increase
When you reach the South Pole, daylight hours
last 24 hours (its summer.
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Didja notice
Seasons are reversed!
Summer in the North Winter in the South.
Spring in the North Autumn in the South.
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Source Windows on the Universe
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And, thats a quick look at the reasons for the
seasons.