EARTH SCIENCE REGENTS REVIEW
UNIT 6 - INSOLATION AND THE SEASONS
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1. INSOLATION – (INCOMING SOLAR RADIATION)
It is the portion of the sun’s output of electromagnetic
radiation that is received by Earth at the outermost part of our
atmosphere.
 ANGLE OF INSOLATION
It is a measure of how high the sun is in the sky. (In the northern
hemisphere the highest angle is on June 21st (summer solstice) and
the lowest angle is on Dec21st (winter solstice).
1. Solar Noon – When the sun reaches its highest position
in the sky.
www.sunflower-solar.com
2. SHADOWS
In order to determine the direction of the shadow, you
must first locate the light source (sun). Your
shadow is always OPPOSITE that light source. For
example, if the sun is in the east, your shadow is in the
west.
SHADOWS - ANNUALLY
Shadows (Annually)

Your shadow is longest when the sun is
lowest in the sky (Dec 21st).

Your shadow is shortest when the sun is
highest in the sky (June 21st).

(This is at the time of solar noon).
Shadows (Daily)

Your shadow is shortest at solar
noon and longest at sunrise and
sunset.
SOLAR NOON
Everyday in New York at solar noon,
the sun is in the SOUTH, therefore
your shadow is always in the
NORTH.
 DURATION OF INSOLATION
It is the length of time (from sunrise to sunset) or daylight period that
the sun appears in the sky.
 June 21st – North Pole (actually above 66 1/2°- Arctic Circle)
receives 24 hours of daylight. (South Pole actually below 66 1/2° –
Antarctic Circle ) receives 24 hours of darkness).
 Dec 21st – North Pole (actually above 66 1/2° – Arctic Circle)
receives zero hours of daylight. (South Pole actually below 66 1/2°
– Antarctic Circle) receives 24 hours of daylight).
NOTE: Over the course of an entire year EVERYONE
on Earth receives the same DURATION OF
INSOLATION (daylight).
www.newyorkscienceteacher.com/photo/displayim...
12 AND 12
24 HOURS OF
DAYLIGHT
24 HOURS OF
DARKNESS
12 AND 12
 INTENSITY OF INSOLATION
It is the rate at which the energy is radiated at some wavelength than
at the others. Generally, the higher temperature of matter, the shorter
the wavelength at which the maximum intensity of radiation. (The
maximum intensity occurs in the range of wavelengths of visible light,
however approximately 48% of the total energy received at the outer
part of our atmosphere is infrared (longer wavelength).
1. The intensity of insolation is greatest when the sun’s rays are
perpendicular (at a 90º angle) to the Earth’s surface.
www.uwsp.edu
INTENSITY
DURATION
 ABSORPTION OF INSOLATION
Only about half (50%) of the solar energy
that reaches Earth is absorbed by the
ground and water. The rest of the energy
is reflected off the Earth or absorbed and
reflected by our atmosphere.
ucar.edu
1. CLOUDS
When clouds are present, much of the incoming solar
energy is reflected back to space. Random reflection, or
scattering of insolation is caused by aerosols (finely
dispersed solids and liquids) suspended in air. Some
examples are ice crystals, water droplets, dust, volcanic
ash and other air pollutants. The more aerosols in the
atmosphere, the less insolation reaches Earth’s surface.
Therefore, when clouds are present:
 The temperature during the day will be
cooler, and the temperature at night will be
warmer.
Therefore, when clouds are NOT present:
 The temperature during the day will be
warmer, and the temperature at night will
be cooler.
2. OZONE LAYER – Nearly all ultraviolet radiation is
absorbed by Earth’s ozone layer (Stratosphere).
nc-climate.ncsu.edu
3. GREENHOUSE EFFECT
GREENHOUSE EFFECT
The process by which the
atmosphere transmits SHORTWAVE(VISIBLE LIGHT)
radiation from insolation (the sun)
and absorbs LONG-WAVE reradiation. (INFRARED
RADIATION).
: www.cityofsydney.nsw.gov
Think
of heat as
infrared
energy.
The
infrared
energy
(heat)
gets trapped by the glass
and can not escape the greenhouse.
PRENTICE HALL
 GLOBAL WARMING
An increase in average Earth temperatures.
 GREENHOUSE GASES
a. Carbon Dioxide
b. Methane
c. Water Vapor
NOTE: These gases are good absorbers of INFRARED
RADIATION which is released by Earth’s surface
(CALLED TERRESTRIAL RADIATION).
2. VARIATION OF INSOLATION
Insolation varies from place to place on Earth’s surface.
A. Intensity
a.
b.
c.
d.
Earth’s shape
Latitude
Seasonal change
Time of day
B. Duration
 Latitude and season
DURATION
3. Relationship of Surface Temperature to Insolation
(also known as Temperature Lag)
NOTE: If the earth receives more heat energy than it
gives off the temperature will rise. If the Earth
gives off more heat energy than it receives the
temperature will go down.
A) Daily Maximum and Minimum Temperatures (N.Y. STATE)
 Greatest amount of Insolation – Solar Noon.
 Hottest time of day - 2-4 pm.
 Coldest time of the day – 5-6 am (right
about sunrise)
B) Annual Maximum and Minimum Temperatures (N.Y.STATE)
 Greatest amount of Insolation – June 21st
 Hottest time of year - July to August
 Least amount of Insolation – December 21st.
 Coldest time of the year – Jan. to Feb.
4. Heat Budget
The balance between the total amount of energy the Earth receives
and the total amount of energy it emits.
1. Heat budget can be measured as the average temperature of
the Earth. If the earth receives more heat energy than it
gives off the temperature will rise. If the Earth gives off
more heat energy than it receives the temperature will go
down. When they are equal the Earth is said to be in
RADIATIVE BALANCE.
** TERRESTRIAL RADIATION - The Earth is always cooling
Off (examples of other terms – ground radiation,
re- radiation, Earth giving off heat)
FACTORS THAT MAY AFFECT THE HEAT BUDGET
ON EARTH
 Changes in Solar Energy – Sunspots are a darker region on
the sun’s visible surface. When there are large numbers of
sunspots the sun emits more energy.
 Changes in Earth’s Orbit and Tilt – Over thousands of years
the tilt of Earth’s orbit changes a few degrees. The season
during which Earths passes closest to the sun varies from winter
to summer. The eccentricity also changes a slight amount.
When the cycles of these factors occur at the same time
summers may be cooler and winters may be warmer.
 Volcanic Eruptions – When there are major volcanic
eruptions, aerosols such as volcanic ash and sulfur compounds
are propelled into the atmosphere and stay there for months or
years. The aerosols make Earth’s atmosphere less transparent to
insolation and reflect a greater than normal amount of
insolation back into space. As a result less energy reaches
Earth’s surface and cooler temperature occur.
 Human Causes – Deforestation (the cutting down of trees –
which absorbs CO2) has resulted in regions becoming hotter
and drier.
5. SEASONS
Astronomical Causes of The Seasons
1. Tilt of the Earth’s Axis
 23 1/2º with respect to a line perpendicular to the plane
of its orbit of the sun.
2. Parallelism Of Earth’s Axis
 Earth’s axis always points in the same direction in space.
3. Revolution of the Earth Around the Sun
 As Earth revolves around the sun, the direction of the
Earth’s axis with respect to the sun varies because of its
tilt and parallelism.
www.fas.org/..