Why Do We Have Seasons? Thats easy! The Earth is closer to the Sun in Summer.
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Transcript of Why Do We Have Seasons? Thats easy! The Earth is closer to the Sun in Summer.
Why Do We Have Seasons?
That’s easy!The Earth is
closer to the Sun in
Summer.
That’s easy!The Earth is
farther from the Sun in
Winter.
That’s easy!Everybod
y knows that!
Wrong!
Didja’ know…The Earth is
closest to the Sun in Winter & farthest in
Summer.
Here’s the Sun thru the Year.
You can actually see the apparent
size of the Sun change.Larger (closer) –
WinterSmaller (farther) -
Summer
If distance from the Sun isn’t
responsible, what is?
Look at EarthThe
Earth is not
straight “up and down.”
The Earth’s axis is titled
23.5°.
Source: Dr. Mike Eracleous’ website, Penn State University
Why?4.5 billion years ago,
Earth was hit by an object the size of
Mars.
Why?This formed
the Moon and knocked the Earth on its side 23.5°.
Why?It also resulted
in the Earth tilting 23.5°.
So why do we have seasons?It’s the tilt,
baby!
Fact: The Earth revolves around the Sun
(click the picture).
Combine the Earth’s tilt and its revolution around the Sun, you get
seasons!
As the Earth revolves around
the Sun, different parts of the Earth tilt towards the
Sun.
SummerEarth tilts
towards the Sun.
Source: Virtual Solar Systemhttp://inkido.indiana.edu/a100/projecthelp.html
WinterEarth tilts away from the Sun.
Source: Virtual Solar Systemhttp://inkido.indiana.edu/a100/projecthelp.html
Autumn/SpringEarth
does not tilt
towards or away
from the Sun.
Source: National Schools’ Observatoryhttp://www.schoolsobservatory.org.uk/news/arch/sky0906.shtml
The tilt affects the
Earth in two important
ways.
The Earth receives
either direct or indirect sunlight
(heat energy).
Direct sunlight (heat energy) is received in the
Summer.Indirect sunlight (heat energy) is received in the
Winter.
Look at this diagram.
Source: ASD Planetariumhttp://www.astronomy.org/programs/seasons/index.html
Look at the diagrams.
Warm – covers
small area.
Look at the diagrams.
Cool – same amount of
sunlight (heat energy) covers
larger area.
Key Season Dates
First day of Summer –
around June 21st.
Key Season Dates
June 21st also has the most daylight hours of any day
in the year.
Key Season Dates
June 21st – The Summer Solstice
(the Sun is farthest north in
the sky).
Why is summer sometimes called “the dog days of
summer? Click below to find out!
Key Season Dates
First day of Autumn– around
September 21st.
Key Season Dates
September 21st –
Autumnal Equinox.
Key Season Dates
Equinox – “equal
nights.”
Key Season Dates
Daylight & nighttime
both last 12 hours.
Key Season Dates
First day of Winter – around
December 21st.
Key Season Dates
December 21st also has the
fewest daylight hours of any day
in the year.
Key Season Dates
December 21st – The Winter
Solstice (the Sun is farthest south
in the sky).
Key Season Dates
First day of Spring –
around March 21st.
Key Season Dates
March 21st – Vernal
Equinox.
Can you really balance an egg only
on the equinox? Click on the egg to see!
The Sun appears to move thru the sky during the
year.This is called an
analema.
Summer
Autumn/Spring
Winter
North South
The second way the tilt affects the
seasons is the number of daylight hours.
The clip on the next slide shows how
daylight changes thru
the year.
When the Earth is tilted towards
the Sun (summer), more of the Northern Hemisphere is in
daylight.
Source: http://www.astro.psu.edu/~mce/A001/lect03.html
At the North Pole, there is 24 hours of sunlight in
the summer.
As you move south, the daylight
hours decrease until you reach the
equator. Daylight hours last 12 hours.
Continue moving south and
daylight hours continue to decrease
When you reach the South Pole, nights last 24
hours (it’s winter).
Source: http://www.personal.psu.edu/faculty/j/e/jea4/earth/climate2.html
At the North Pole, night
lasts 24 hours in the
winter.
As you move south, the daylight
hours increase until you reach the
equator. Daylight hours last 12 hours.
Continue moving south and daylight hours continue to
increaseWhen you reach the South Pole,
daylight hours last 24 hours (it’s
summer.
Didja notice…Seasons are
reversed!Summer in the North – Winter in
the South.Spring in the North – Autumn in the
South.
Source: Windows on the Universe
And, that’s a quick look at the reasons
for the seasons.