Download Chapter 2 Solar Energy to Earth and the Seasons

Chapter 2 Solar Energy to Earth
and the Seasons
© 2015 Pearson Education, Inc.
Learning Objectives
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Distinguish between galaxies, stars, and planets.
Locate Earth in the Solar System and Galaxy.
Reconstruct Earth’s annual orbit about the Sun.
Describe the Sun’s operation.
Explain the characteristics of the solar wind.
Explain the characteristics of the electromagnetic spectrum
of radiant energy.
•  Illustrate the interception of solar energy and its uneven
distribution at the top of the atmosphere.
•  Define solar altitude and daylength.
•  Describe the annual variability of solar altitude, solar
declination, and daylength—Earth’s seasonality.
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Milky Way Galaxy
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Dimensions and Distances
•  In astronomy, what is the unit we use for
distance?
–  light-year: distance that light travels in
one year
–  light speed: 300,000 km/s
–  1 light-year (ly) = 9.5 trillion km
Light year is a unit of distance!!!
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Our Solar System
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Earth’s Orbit
•  Earth’s orbit around the Sun is presently
elliptical— a closed oval path.
•  Plane of Earth’s orbit about the Sun is called
the plane of the ecliptic.
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Our Solar System
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Earth’s Orbit
•  Earth’s orbit around the Sun is presently
elliptical— a closed oval path.
•  Plane of Earth’s orbit about the Sun is called
the plane of the ecliptic.
•  Average distance from Earth to the Sun is
150,000,000 km.
•  Light reaches Earth from the Sun in about 8
minutes and 20 seconds.
•  Perihelion—closest on January 3
– 147,255,000 km
•  Aphelion—farthest on July 4
– 152,083,000 km
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Aphelion and Perihelion
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What is Solar Energy?
•  Energy is the capacity of a physical
system to do work. The unit is Joule (J).
•  Solar energy is radiant energy (i.e.,
radiant light and heat) from the Sun.
•  Solar energy is generated by the
nuclear fusion reaction process in which
pairs of hydrogen nuclei are joined, form
helium, and emit a large amount of
energy.
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How is solar energy created?
Solar energy is generated by nuclear fusion reactions.
Pairs of hydrogen nuclei are joined, form helium, and emit
large amount of energy.
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Energy Sources
Renewable energy: can be replenished in a short period of time
Non-renewable energy: cannot be recreated in a short period of time
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Sunspots
•  Sunspots are caused by
magnetic storms on the Sun.
They are more than 12 times
Earth’s diameter.
•  Their temperatures are less
than the temperatures of their
surroundings.
•  Sunspots have an activity
cycle of 11 years.
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Sunspots and Solar Wind
•  Sunspots can produce the solar wind.
•  Solar wind is clouds of electrically charged
particles, and takes about 3 days to
reach Earth.
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Solar Wind Effects
auroras
Magnetosphere deflects the solar wind toward both of
Earth’s poles and only a small portion of it enters the atmosphere.
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Sunspots and Solar Wind
•  Sunspots can produce the solar wind.
•  Solar wind is clouds of electrically charged
particles, and takes about 3 days to
reach Earth.
•  The magnetosphere deflects the solar
wind toward both of Earth’s poles and only
a small portion of it enters the atmosphere
and produces auroras.
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Auroras
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Solar Radiation
•  Solar radiation occupies a portion of the
electromagnetic spectrum of radiant
energy.
•  This radiant energy travels at the speed
of light to Earth.
–  Light reaches Earth from the Sun in about
8 minutes and 20 seconds.
•  The total spectrum of this radiant
energy is made up of different
wavelengths.
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Wavelength and Frequency
Which wave has
higher energy?
Higher frequency is associated with shorter wavelength and higher energy.
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Shorter
The
Electromagnetic
Spectrum
Solar radiation consists of:
1. Gamma rays, X-rays, UV (8%)
2. Visible light (47%)
3. Infrared (45%)
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8%
47%
45%
longer
100%
solar
radiation
The Electromagnetic Spectrum of Radiant
Energy
•  High frequency is
associated with small
wavelengths and high
energy.
•  Solar radiation
consists of three parts:
1)  Gamma rays,
X-rays, UV (8%)
2)  Visible light (47%)
3)  Infrared (45%)
Absorption by CO2,
water vapor, and
other gases
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Solar and Terrestrial Energy Distribution
by Wavelength
•  High energy (or shortwave radiation) is
associated with high temperature,
--- solar energy is shortwave radiation.
•  Low energy (or longwave radiation) is
associated with low temperature,
--- terrestrial energy is longwave radiation.
•  Why? Sun’s surface temperature is about
6000K, and the average Earth’s surface
temperature is about 288K.
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Earth’s Energy Budget
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Insolation
•  Solar radiation that reaches a horizontal
plane at Earth is called insolation, i.e.,
incoming solar radiation.
•  Insolation at the top of the atmosphere is
expressed as the solar constant (1372W/
m2).
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Distribution of Insolation
•  The thermopause (480 km) above Earth’s
surface is the outer boundary of Earth’s
energy system.
•  Earth only receives one two-billionth of
Sun’s total energy output.
•  Tropics receive more concentrated
insolation due to Earth’s curvature.
•  Tropics receive more than 2.5 times
of what poles receive.
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Solar Energy Received at Earth’s Surface
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Insolation Receipts and Earth’s
Curved Surface
•  Subsolar point is the location where
insolation is perpendicular to the surface.
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Figure 2.9
Subsolar point
Subsolar point is the location where insolation
is perpendicular to the surface.
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Figure 2.9
Insolation at Top of Atmosphere
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Average Daily Net Radiation
•  Net Radiation = Incoming Shortwave
Radiation − Outgoing Longwave Radiation
Recall the conservation law of energy: Input Energy-Output Energy=Storage Change
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Sun’s altitude, declination, and daylength
•  Sun’s altitude is the angle between the
horizon and the Sun. At sunrise or sunset, the
Sun’s altitude is 0°. If the Sun reaches the
point directly overhead, it is at 90° altitude.
•  The Sun’s declination is the latitude of the
subsolar point (between 23.5°N and 23.5°S).
•  Daylength is time between sunrise and
sunset.
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The Seasons
•  Seasonality: the seasonal variation of the
Sun’s position above the horizon and
changing daylengths during the year.
•  Reasons for seasons
•  Annual march of the seasons
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Five Reasons for Seasons
1)  Revolution
2)  Rotation
3)  Tilt of Earth’s axis
4)  Axial parallelism
5)  Sphericity
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Reasons for Seasons
1)  Revolution
– Earth revolves around the Sun.
– Voyage takes one year.
2)  Rotation
– Earth rotates on its axis once every
24 hours.
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Revolution and Rotation
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Reasons for Seasons
3)  Tilt of Earth’s axis
–  Axis is tilted 23.5° from plane of ecliptic.
4)  Axial parallelism
–  Axis maintains alignment during orbit around
the Sun.
–  North pole points toward the North Star
(Polaris).
5)  Sphericity
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Axial Tilt and Parallelism
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Annual March of the Seasons
•  Winter solstice—December 21 or 22
–  Subsolar point at Southern Tropic (23.5°S)
•  Spring equinox—March 20 or 21
–  Subsolar point at Equator
•  Summer solstice—June 20 or 21
–  Subsolar point at Northern Tropic (23.5°N)
•  Fall equinox—September 22 or 23
–  Subsolar point at Equator
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June Solstice (Summer Solstice)
June 20-21
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September Equinox (Autumnal Equinox)
September 22-23
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December Solstice (Winter Solstice)
December 21-22
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March Equinox (Vernal Equinox)
March 20-21
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Seasonal Observations
40°N
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Annual March of the Seasons
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Daylength Times
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Summary of Chapter 2
•  Our Solar System is located on a remote, trailing edge of the
Milky Way Galaxy, a flattened, disk-shaped mass estimated
to contain up to 400 billion stars.
•  In its orbit, Earth is at perihelion (its closest position to the
Sun) during our Northern Hemisphere winter (January 3). It is
at aphelion (its farthest position from the Sun) during our
Northern Hemisphere summer (July 4).
•  Sunspots are caused by magnetic storms on the Sun.
•  Solar wind is clouds of electrically charged particles, and
takes about 3 days to reach Earth.
•  Solar radiation occupies a portion of the electromagnetic
spectrum of radiant energy. Solar radiation that reaches a
horizontal plane at Earth is called insolation.
•  Five reasons of seasons: 1) revolution, 2) rotation, 3) tilt of
Earth’s axis, 4) axial parallelism, and 5) sphericity.
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