EARTH-SUN
RELATIONSHIPS
Insolation, Day-Night and Seasons
1. Cosmic Connections:
Earth, Solar System and Beyond
2. The Sun and Solar Radiation:
Insolation, Solar Energy and Atmospheric Dynamics
3. Earth’s Geometry and Movements:
Day-Night, Length of Day, Seasons, Latitudinal Zones
1. COSMIC CONNECTIONS:
EARTH, SOLAR SYSTEM AND BEYOND
Physical Geographers examine Earth’s relationships with the Sun
and other heavenly bodies to explain such earthly phenomena as:
1) day and night,
2) seasonal variations,
3) climatic variations, and
4) certain atmospheric anomalies.
• Earth is almost entirely dependent on the Sun for its existence!
• Earth, together with seven other planets, form our Sun’s
Solar System
A Solar System comprises all celestial bodies surrounding and orbiting
a particular star due to the star’s dominant mass and gravitational
attraction.
Earth and the Solar System
• All the planets revolve around the Sun in the same direction
• All the planets lie in a common plane – the Plane of the Ecliptic,
and the orbits of the planets are nearly circular
 The Sun has a relatively slow rotation [What happened to Pluto?]
Two Groups of Planets:
Inner planets are made of rocks
and metals – Terrestrial Planets
Outer planets are made of gases
and ices – Gas Giants
Our solar system also includes about 138 satellites (like our moon),
numerous asteroids, as well as comets and meteors (“shooting stars”
and meteorites)[Does our moon have any impact on our environment?]
And our Sun is one of an estimated 400 billion stars that make up
our
Galaxy – the Milky Way Galaxy.
• All the stars that you see on a clear night are part of our
Milky Way Galaxy
• Galaxies are sprawling space systems composed of countless
clusters of stars, dusts and gases
• Billions of galaxies – so far apart that measured in light years
(1 light year = 6 trillion miles; speed of light is 186,000 mps)
• The closest galaxy to ours is 75,000 light years away
• Some of these distant systems are similar to our own Milky
Way Galaxy, while others are quite different
These are, then, our planet’s –
Cosmic Connections
See also:
http://www.youtube.com/watch?feature=endscreen&v=_IVqMXPFYwI&NR
=1
2. THE SUN AND SOLAR RADIATION
The Sun and Its Energy
• The sun is a self-luminous sphere
of gasses that emit radiant energy.
• Our Sun, then, is like a giant thermonuclear furnace with fusion
reactions, and a core temperatures exceeding 27,000,000˚ F
• At its luminous outer surface, the Photosphere, temperatures fall to
10 -11,000˚F – then the Chromosphere, and then the Corona
• Charged particles (protons & electrons) from the corona flow along the
sun’s magnetic field lines into space as Solar Wind – interacts
with ions in earth’s outer atmosphere to produce the colorful light
shows, the Auroras (Aurora Borealis and Aurora Australis)
Sunspots, caused by magnetic storms on the sun, are dark regions on the
photosphere, 15000 C - 20000 C cooler than the surrounding. → They signify
increased solar activity, peaking in 11- year cycles → The last peak was
estimated to be in 2012 (Remember the recent movie, “2012” ?)
Solar Flares / Solar Storms (accompanied by coronal mass ejections
or CMEs) occur in the region of sunspots, sending out energized, charged
particles at great speeds toward the earth. . . May cause massive disruptions
and destructions on earth, e.g., crashing the power grid, as happened in
Quebec in 1989.
Insolation and Atmospheric Dynamics
• Incoming solar radiation, or insolation, is the major source of energy
both directly and indirectly for the entire solar system
The rate of a planet’s receipt of solar energy is called the solar constant
• Sun’s energy is emitted as electromagnetic energy, travelling in a
spectrum of varying wavelengths, taking 8.3 min. to reach earth
• This radiant energy is largely shortwave radiation (9%), composed of
Ultraviolet rays, X-rays and Gamma rays; visible light (41%);
various infrared wavelengths (49%); and microwave,
television and radio wavelengths (1%)
 Notably, earth receives only 1/2,000,000,000 (one two billionth) of
the sun’s radiation ← but that’s what drives much of the
atmospheric, physical and biological processes on our earth.
 However, Spatial and Seasonal Variations in Insolation occurs
over the surface of the earth due largely to 3 factors:
1. Duration of daylight (varies by latitudes and seasons);
See Table 3.1, p. 53 in Text
1.
2. Angle of solar rays (which affects intensity); and
3. Earth’s atmosphere (some radiation is absorbed by
clouds, some reflected back). Unlike solar radiation, earth
radiation is longwave radiation
 The first two factors above relate to:
Earth’s Geometry and Movements
– and their Implications and Effects
→
3. EARTH’S GEOMETRY AND MOVEMENTS:
Day-Night, Length of Day, Seasons, Latitudinal Zones
3 aspects of earth’s geometry, and 3 basic movements of the
earth have profound, intertwined effects on our environment.
First, the 3 aspects of earth geometry:
1.
2.
3.
SPHERICITY
AXIAL TILT – INCLINATION
AXIAL PARALLELISM
1. SPHERICITY
Earth appears as an oblate
spheroid to the Sun’s
parallel rays; the geoid
Effects of Earth’s
2. AXIAL TILT – INCLINATION
and Plane of Ecliptic
Earth’s axis is tilted about 23.5˚ from
perpendicular the Plane of Ecliptic;
this tilt has two characteristics:

Angle of Inclination

Axial Parallelism
3. PARALLELISM
Earth’s axis remains in a fixed alignment with Polaris directly overhead,
throughout the year, as it revolves about the Sun
Next, 3 Basic Movements of the Earth:
1. ROTATION; 2. REVOLUTION
3. GALACTIC MOVEMENT
1. ROTATION
 The Earth rotates on its axis
 One complete rotation (3600) takes
approximately 24 hours
 Rotation is from West to East
Sun appears to ‘rise’ in East and ‘set’ in West
 Two Types of Rotation
Velocity:
 Angular Velocity – constant
 Linear Velocity – fastest at the
equator, decreases to 0 at the poles
2. REVOLUTION
 The Earth revolves around the Sun in one year (365.25636 days)
 The Earth’s revolution is slightly elliptical, not circular –
Direction of revolution is counter-clockwise
 Earth moves in a constant plane – Plane of the Ecliptic – in its revolution
about the Sun – Earth’s Orbit
The Orbit of the earth is an elliptical path along the Plane of Ecliptic
Average orbital length = 940,416,480 km
Average orbital velocity = 29.8 km/s
Closest approach to the Sun = 147 million km, Perihelion (January 3)
Farthest distance from the Sun = 152 million km, Aphelion (July 4)
3. GALACTIC MOVEMENT
 Movement of the earth with the sun and the rest of the solar system in an
orbit around the center of the Milky Way Galaxy.
 This movement apparently has limited perceptible effect on the changing
environment of the earth.
However, could there
be long-term effects?
• Earth’s axis wobbles
through time (22˚- 24.5˚)
and will not always
maintain a constant angle
• Earth’s orbit around the sun will
also change from more circular to more elliptical
(Milankovitch Cycles) [Explains Cycle of Ice Ages?]
• Why?
IMPLICATIONS AND EFFECTS:
 Alternating Day and Night
• Caused by earth’s rotation
– Circle of Illumination
 Length of Day and Seasons
12-hour days year-round at the equator, greater
variability toward the poles, with the poles alternately
experiencing essentially one long 6-month long day,
and a similarly long night.
– Variations due to:
 Inclination of earth’s axis
 Plane of Ecliptic, and Parallelism; and
 Earth’s revolution around the sun,
which results in:
 2 Solstices (Summer, Winter)
 2 Equinoxes (Vernal, Autumnal)
In the Northern
Hemisphere,
A: Summer
Solstice*
B: Autumnal
Equinox
C: Winter Solstice*
D: Vernal Equinox
*During[See:
the 2 Solstices,
Figures 3.5 & 3.6
the situations are reversed
in Text, and Read the
in the Southern
Hemisphere
Explanation ]
2 Solstices →
The Sun’s Rays in
Summer (b) and Winter (c)
(Angle of the Sun)
2 Equinoxes →
Percentage of Insolation
striking various latitudes
during an equinox
(Sphericity)
The combined effect → Seasonality
To summarize:
4 Seasons
(or 6, as in Asia)
5 Reasons for Seasons:





Sphericity
Axial Tilt
Parallelism
Rotation
Revolution
Sun’s Migration
Across the Sky
and
The Analemma
 Subsolar Point
 Sun’s Declination
 Sun’s Altitude
 Why the sun can never
be seen directly overhead
in Los Angeles?
 Latitudinal/Spatial Variations
6 Latitudinal Zones
of Insolation and Temperature
1.
2.
3.
4.
5.
6.
North Tropical
North Middle-Latitude
North Polar or Arctic
South Tropical
South Middle-Latitude
South Polar or Antarctic
LATITUDINAL GEOGRAPHIC
ZONES
ONLINE EXERCISE
ANSWER THE FOLLOWING QUESTIONS IN RELATION TO THE DIAGRAM BELOW:
a) Name the locations marked by numbers on the diagram of the earth. (Identify Antarctic Circle, Arctic Circle, Axis
of Rotation, Equator, Tropic of Cancer, and Tropic of Capricorn)
1 _______________________________
2 _______________________________
3 _______________________________
4 _______________________________
5 _______________________________
6 _______________________________
b) If you were looking down on the North Pole from outer space, in what direction would the earth be turning?
(clockwise or counterclockwise?)
c) At what point or line on the earth’s surface is the sun overhead at noon?
d) What date of the year is represented by the earth in this position relative to the sun?
e) Where is the “land of the midnight sun” according to this diagram?
f) What changes would take place in terms of daylight hours and seasons if earth’s revolution around the sun took
two years instead of one? Speculate and elaborate.