The Universe contains millions of Galaxies one of
which is our own MILKY WAY GALAXY. The Milky Way consists of up to 400
billion stars similar to the SUN. It is believed that the SOLAR SYSTEM
condensed from a large rotating cloud of dust and gas called a NEBULA. This
occurred about 4.6 billion years ago.
Gravity is the mutual attracting force exerted by the mass
of an object upon all surrounding objects.
DISTANCE & EARTH’S ORBIT.
Light
travels through space at a speed of 186,282 miles per second (299,792 km per
sec). About 6.0 trillion miles (9.5 trillion kms.) per year. The distance (6.0
trillion miles) that light travels in a year is termed LIGHT YEAR and is
used as a unit of measurement in the vast universe. Examples are:
1.
The moon is 238,866 miles from the earth. This is about 1.28 seconds light speed
2.
The diameter of the Solar System is 11 hours light speed
3.
The Milky Way (from side to side) is 12 billion light years.
Earth’s
orbit around the Sun is ELLIPTICAL – a closed oval shaped path.
Average
distance from Earth to the Sun is 93 million miles (150 million kms).
Light from the Sun reaches the earth in about 8 minutes and 20 seconds.
The Earth is at Perihelion (its closest distance to the Sun) on January
3, at 91,500,000 miles.
On
July 4th, the Earth is at Aphelion (longest distance from the Sun) at 94,500,000
miles. The distance between Perihelion and Aphelion result in a 3.4%
variation in Solar Radiation output on Earth
RADIANT
ENERGY.
The
Sun’s principal outputs are Solar Wind and Radiant Energy. The
Sun produces tremendous quantities of energy through Fusion.
What
is FUSION? Under great
temperature and pressure conditions in the Sun’s core, pairs of hydrogen
nuclei (lightest of all natural elements) are forced to fuse together. This
creates an unstable form of helium (Helium-3) and releases a neutron
as energy. Helium-3 fuses further with some
hydrogen that has an additional neutron (deuterium hydrogen atom) to form
a stable Helium-4 and releases proton as energy.
Every
second, a
conversion of hydrogen to helium with the release of energy takes place in the
Sun’s core. So far, the Sun has converted only 8% of its mass of helium.
Sun’s surface temperature is 11,0000F (60000C).
Rate
of energy production in the Sun’s core is nearly constant so output of
Solar Radiation is Constant. Solar Constant is about 1370 Watts per
square meter. It is measured at outer limits of earth’s atmosphere.
Sunspots
are huge magnetic storms that reveal unusual solar activity at regular cycles
averaging eleven years (7-17 years) from maximum peak to maximum peak.
RECENT
SUNSPOT CYCLE ACTIVITY
1976
– Solar Minimum
1979
– Solar Maximum (100 sunspots visible)
1986
– Solar Minimum
1990
– Solar Maximum (Over 200 sunspots)
1997
– Solar Minimum
2001
– Solar Maximum (Low sunspots)
Solar
Wind: An
outward surge of electrically charged particles (electrons and protons)
from the Sun towards the Earth. Solar Winds grow stronger during periods of
increased SUNSPOT activity. A magnetic field at the outer layer of the earth’s
atmosphere (magnetosphere) deflects Solar Winds toward the poles so that
only a small portion enters the atmosphere.
Impacts
of Solar Winds & Sunspots:
a)
Creates AURORAS (radiation of light energy in varying colors).
b)
Disrupts radio and satellite broadcasts
c)
Causes overload on electrical systems
d)
Distorts weather patterns - Wet periods coincide with every other Solar Maximum
and Droughts occur with every other Solar Minimum.
ELECTROMAGNETIC
SPECTRUM & RADIANT ENERGY
All
objects emit radiant energy. (Light and heat are familiar examples). Light is a
radiation that is visible to the human eye. The human body feels radiant heat
energy, though it is not visible.
Radiant
energy from the Sun is termed Electromagnetic Radiation. Consists of a
range of wavelengths (spectrum). A wavelength refers to the distance
between one crest and the next wave crest. Wavelengths are measured in
micrometers, (one-millionth of a meter 10-6).
Energies
in the Electromagnetic Spectrum.
1.
Gamma and
X-ray: very short wavelength hence
high energies - harmful to human health.
2.
Ultraviolet
10 to 400 nanometers (0.4 micrometers). UV can damage human tissues.
3.
Visible
Light
0.4 to 0.7 micrometers.
4.
Near-Infrared
0.7 – 1.2 micrometers.
5.
Infrared
radiation 1.2 – 3.0
micrometers
6.
Middle
infrared 3
– 6 micrometers.
7.
Thermal
Infrared 6 to 300
micrometers.
8.
Microwave
energy 1 cm onwards
9.
Radar
about 0.1 – 1 centimeter
10. TV & Radio signs 10 to over 100 cms.
Principles
of Electromagnetic Radiation:
1.
An
inverse relationship
exist between an object’s temperature and the wavelengths of radiation that
the object emits. (The Hot objects (Sun) emit short waves and cool objects
(Earth) emit long wave radiation “heat”).
2.
The
flow of radiant energy from an object is directly related to the absolute
temperature of the objects surface raised to the fourth power.
The Output of solar radiation is significantly
reduced by the earth's atmosphere through scattering and absorption.
Absorption: Absorption occurs when molecules and particles in the
atmosphere intercept and absorb solar radiation at particular wavelengths.
Atmospheric
absorption is important because it warms the atmosphere directly.
Most important Atmospheric Absorbers are:
a) Ozone
and Oxygen (wavelength less than 0.3 microns)
b) Carbon
Dioxide (variable wavelengths)
c) Water
Vapor (variable wavelengths)
Scattering: Scattering refers to a turning aside of radiation by
molecules or particles so that the direction of the ray would change. Scattering
of short-wave radiation illuminates the sky and gives it the blue
color. Without scattering, the sky would be dark. This diffuse radiation is
termed as skylight or sky radiation. Within the visible spectrum,
skylight is composed primarily of blue color wavelengths.
The flow of Solar Radiation to the Earth is termed INSOLATION
= (Incoming – Solar – Radiation) Insolation measures the amount of solar
power available to heat the land’s surface and atmosphere. The amount of
insolation received on the earth’s surface varies from place to place and time
to time.
The
amount of daily Insolation received at the earth’s surface depends upon two
main things:
1.
The angle at which the Sun’s rays strike the earth.
Insolation is greatest when the Sun is directly overhead and the Sun’s rays
are vertical. When the sun is lower in the sky, the same amount of solar energy
spreads over a greater area of ground so insolation is lower. At lower angles,
solar energy might also travel a longer distance through very dense dust
particles that absorb some of the energy.
2.
The length of time of exposure to Sun’s Rays.
Latitude at the location and the time of the year control the 2 factors.
The Sun provides constant flow of shortwave radiation
toward the earth. The earth absorbs the shortwave radiation and emits long wave
radiation (heat) to the outer space. The balance between incoming short wave and
outgoing long wave radiation is termed Global Net Radiation. In middle
and high latitudes, (poleward of 360 N & 360S
latitudes, Net Radiation is Negative. The Earth loses more heat to space
than it gains from the Sun. Largest Net Radiation values are found above
Tropical Oceans along the Equator.
Annual insolation is greater at low latitudes.
Insolation changes from a HIGH value at the equator where the Sun is directly
overhead at noon everyday to ZERO at the poles where the Sun is never overhead
and always just on the horizon.
The division of the Globe into broad latitudinal
zones based on seasonal pattern of daily insolation:
1) Equatorial Zone: 100N to 100S
of the Equator. Intense insolation throughout the year.
2) Tropical Zones: Between 100 and
250 North and South Latitudes. Marked seasonal cycle of wet and dry
seasons and high insolation
3) Subtropical Zones: Between 250
and 350 North and South Latitudes. Transitional regions.
4) Mid-Latitude Zones: Between 350 and
550 North and South Latitudes. Strong seasonal contrasts in
insolation and four distinct seasons.
5) Subarctic & Subantarctic Zones: From 550
to 750 North and South Latitudes. Large annual variation in day
lengths results in vast changes in insolation from solstice to solstice.
6) Polar Zones: Between 750 and the
poles. A regime of 6-month day and 6-month night is predominant. Greatest
seasonal contrasts in insolation.