Seasons review
Bill Nye! (4 min)
Outline Notes:
Big Idea:
The seasons are the result of:
1) the tilt of the Earth's axis, and
2) revolution around the sun
• If
the tilt of the Earth's axis was 0°
there would be no difference in how
the rays from the sun hit its different
regions (there would be no seasons)
Equinoxes and Solstices
Quick reminder!
Label on your page now!
What is a solstice?
• either
the shortest day of the year (winter solstice)
or the longest day of the year (summer solstice)
Make a quick T chart
in your notes – title it “Solstice”
Winter Solstice
Summer Solstice
Winter Solstice
•
During the December Solstice the Sun’s rays shine on the Tropic of
Capricorn.
•
Happens on or around December 21st (the tilt is 23.5S)
•
At the December solstice, the Northern Hemisphere is leaning the most
away from the sun for the year.
•
All locations south of the equator have day lengths greater than 12 hours
at the December solstice.
•
Meanwhile, all locations north of the equator have day lengths less than
12 hours.
•
For us on the northern part of Earth, the shortest day comes at this
solstice. After the winter solstice, the days get longer, and the nights
shorter.
Winter Solstice
•
Stonehenge is carefully aligned on a sight-line that points to the winter solstice sunset. This
Stonehenge monument – built in 3,000 to 2,000 BC – shows how carefully our ancestors watched
the sun. Stonehenge is perhaps the most famous of the ancient astronomical monuments found
around the world.
Winter Solstice
• The northern hemisphere is pointed furthest away from the sun
• The sun is directly over the Tropic of Capricorn
• The shortest day of the year in the northern hemisphere
Summer Solstice
•
During the June Solstice the rays of the Sun shine directly on the Tropic
of Cancer.
•
Happens on or around June 21st (the tilt is 23.5N)
•
At the June solstice, the Northern Hemisphere is leaning most toward
the sun for the year.
•
All locations north of the equator have day lengths greater than 12
hours at the June solstice.
•
Meanwhile, all locations south of the equator have day lengths shorter
than 12 hours.
•
For us on the northern part of Earth, the longest day comes at this
solstice. After the summer solstice, the days get shorter, and the nights
longer.
Summer Solstice at Stonehenge
Summer Solstice
• The northern hemisphere is pointed furthest toward the sun
• The sun is directly over the Tropic of Cancer
• The longest day of the year in the northern hemisphere
Summer solstice in the artic
• The
sun never sets!
So an equinox is…?
•
Equinox: the date (twice each year) at which the sun crosses
the equator, therefore day and night are of equal length (about
September 22 and March 20).
Equinox (means – Equal night )
 Equinoxes are halfway between the solstices, neither
hemisphere is tilted toward or away from the sun
 The noon sun is directly overhead at the equator
 There are 2 equinoxes, the vernal and autumnal - these
classical names are direct derivatives of Latin
(ver = spring and autumnus = autumn)
Video: National Geographic (3 min)
Make another quick T chart
in your notes – “Equinoxes”
Spring (Vernal)Equinox
Fall Equinox
Spring and Fall Equinox
• Vernal (spring) and autumnal (fall) equinox - the
sun is directly over the equator
• Days and nights are equal in length
Vernal (Spring) Equinox
• March
21st
• Marks
the beginning of spring
in the northern hemisphere
• The
March equinox marks the
moment the Sun crosses the
celestial equator – the
imaginary line in the sky
above the Earth’s equator –
from south to north
Celestial Sphere
•
As people first started to map out the
night sky, it became necessary to have a
standard, way of plotting objects in the
sky.
•
As the stars appear to occupy fixed
positions in the sky relative to each other,
a convenient way of thinking about the
situation would be to imagine the Earth
placed at the center of a larger sphere.
•
The stars occupy fixed positions on the
surface of this 'celestial sphere', and the
Earth rotates within it.
•
This is obviously not the case in real life
but it is a good model because this is
pretty much how things look from our
point of view.
Celestial
Equator
Autumnal Equinox
• September
23rd
• Marks
the beginning of fall in
the northern hemisphere
• The
September equinox
marks the moment the Sun
crosses the celestial equator –
the imaginary line in the sky
above the Earth’s equator –
from north to south
Equinoxes and Solstices
Video for review
• Summary
video http://www.tamingdata.com/2010/12/21/the
-winter-solstice-explained-science-version/
What to do now:
Daylight Map:
Activity help: