Transcript Seasons

Aim: What is the reason for the seasons?
Seasons animation
Seasons diagram in Northern Hemisphere
A: Two Reasons:
 1. The
tilt of the Earth’s axis
a. When a hemisphere is tilted toward the Sun, the
season is summer
b. When a hemisphere is tilted away from the Sun, the
season is winter.
 2. The
revolution of the Earth around
the Sun
– The hemisphere that points toward the Sun changes as
the Earth revolves around the Sun = causes seasons to
change.
B. Earth’s tilt creates uneven heating
 The earth is tilted 23.5 o in
relation to the sun.
 The tilt causes the sun to hit
the earth at different
angles….causing different
temperatures.
 This is called the angle of
insolation. Higher
angles=stronger sunlight
ESRT – periods of revolution
Planets
Period of Revolution Around the Sun
Mercury
87.96 Earth days
Venus
224.68 Earth days
Earth
365.25 days
Mars
686.98 Earth days
Jupiter
11.862 Earth years
Saturn
29.456 Earth years
Uranus
84.07 Earth years
Neptune
164.81 Earth years
Pluto (dwarf planet)
247.7 years
Which planet is going:
Fastest?
Slowest?
The farther the planet…the faster the orbital speed!
Questions…
If the Earth’s orbit is a 360o ellipse,
and it takes 365.25 Earth days to
revolve….
Approximately how many degrees per day
does the Earth travel in its revolution?
A) 1
B) 3
C) 10 D) 30
C. Definitions
 1. Revolution: The movement of a planet in its orbit
around the Sun.
 2. Orbit: The path a planet takes around the Sun.
 3. Path is slightly oval shaped called an ellipse.
An oval shaped orbit is referred to as elliptical. The
farther away the planet, the longer the period of
revolution.
 4. Season: The change in temperature caused by the
earth’s tilt as it revolves around the sun.
D. Seasons have nothing to do with distance…
the N.H. is in summer when Earth is farther
away from the sun.
E. Animations of the
The Earth’s Orbit
Earths Orbit
seasons animation
Label Seasons diagram….
The Tropics
F. What is a solstice? When the Sun’s direct
rays (strongest) reach farthest north or
farthest south of the equator.
1.
2.
3.
Sunrise: N of E
Sunset: N of W
Summer Solstice in
N.H.– June 21
First Day of Summer,
longest daylight hours
Strongest (direct) rays
hit north of equator
at the tropic of cancer
(noon sun directly
overhead)
1. Winter Solstice in
N.H.– December 22
2. First Day of Winter,
shortest daylight
hours.
3. Strongest (direct)
rays hit south of the
equator at the tropic
of capricorn (noon
sun directly
overhead)
Sunrise: S of E
Sunset: S of W
G. What is an Equinox?
 1. The direct rays of the
Sun are striking at the
equator (noon sun directly
overhead)
 2. All places on Earth
have equal hours of
daylight and night
– Autumnal Equinox
• First Day of Fall in N.H.,
September 21
– Vernal Equinox
• First Day of Spring in
N.H., March 21
Sunrise: due E
Sunset: due W
Varying daylight hours….
Summer in the Arctic
http://www.youtube.com/watch?v=J9eCK7
rWMNE
Seasons animation
http://kids.msfc.nasa.gov/earth/seasons/EarthSeasons
sun at solstice in north pole
Summary – effects of Earth’s tilt
Seasons (Angle if insolation)
– Higher angle = warmer season
– Lower angle = cooler season
– Little change at the equator = no seasons
Different amounts of daylight hours
(duration of insolation)
– Longer duration = warmer days
– Shorter duration = cooler days
Insolation Chart
Intensity of
Insolation (season)
Date it Occurs
Angle of Insolation
(Highest arc of the
sun)
Duration of Insolation
( # daylight hours)
Location of the
Direct Rays
(Latitude)
Diagram
-------------------
------------------------------
----------------------------
--------------------------
--------------------------
Maximum
insolation (most)
Summer
Average Insolation
Spring
-------------------------Autumn
Minimum insolation
(least)
Winter
Apparent Path of the Sun
Aim: Why do we get differing
amounts of daylight hours during the
year?
A. Why do we get different amounts
of daylight hours during the year?
1.
The tilt of the Earth’s axis makes the sun
appear to rise to different heights during
different seasons.
2.
Summer – sun rises higher, takes longer to set,
longer daylight hours, shorter shadows, more
intensity and duration of insolation.
3.
Winter – sun rises lower, takes less time to set,
shorter daylight hours, longer shadows, less
intensity and duration of insolation.
View of Sun in N. H. at noon
At the equator….
Noon sun at different latitudes
KNOW THESE DIAGRAMS!
EQUATOR
N. Hemi
N. Pole
S. Hemi
Factors Affecting Insolation
 Intensity (strength):
– Atmosphere
(clouds)
– Latitude
– Seasons
– Time of Day
 Duration (length):
– Latitude
– Season
Surface temperatures….
 The Earth’s surfaces take time to absorb and heat
the air…so the warmest time of the day is late
afternoon, even though the strongest intensity of
insolation is at noon.
 Same applies for seasons….strongest intensity is
in June when the sun is most direct overhead, but
it takes a couple of months to heat the oceans and
land…so the warmest month tends to be August.
Climate change in history –
Milaknovitch cycles
 Earth wobbles like a top – every 26000 yrs.
 Earth’s orbit becomes more elliptical – every
100,000 yrs.
 Tilt changes from 23.5 to 24.5 every 41000 yrs.
 Milankovitch cycles on four different periods:
19,000, 23,000, 41,000 and 100,000 years.
 Thought to trigger ice ages
More seasons animations
Brainpop.com