This is Duane Friend with
University of
Illinois Extension.
If we did not have the
benefit of sunlight,
the Earth would be a
cold, frozen mass.
Almost all energy
that we have or use
on the Earth can be
traced back to sunlight.
How does energy from
the sun heat the Earth?
First, the sun must
create the energy
we call sunlight.
This is done
through a process called
fusion.
Because of the
extreme heat and pressure
found in the
center of the sun,
atoms of hydrogen are
combined to form helium.
It's estimated
that 600 million tons of
hydrogen are
fused into 596 million
tons of helium
every second.
Four million tons
of that mass is
converted into energy.
The output of energy,
while varying
slightly from year to year,
is fairly constant.
This energy takes
a long time to
work its way up to
the sun's surface.
Once it escapes,
it travels in the form of
many wavelengths of energy,
most of it being
invisible to our eyes.
The energy travels at
186 thousand
miles per second.
It takes a little over
eight minutes for
sunlight to reach the Earth
after it leaves the sun.
Once reaching Earth, the
more powerful
and dangerous forms
of sunlight are filtered and
absorbed by the
upper atmosphere.
Most of the remaining
wavelengths
of sunlight
travel through
the atmosphere
to get absorbed
and to heat the
Earth's surface.
A small amount
is absorbed by
gases and reflected
back to space.
This helps
explain why it gets cooler
the higher you
go in the atmosphere.
Because the Earth's
atmosphere is
mostly heated from
the Earth's surface.
The Earth re-emits
this energy
in the form of
longer wavelengths.
As this energy moves up
through the atmosphere,
some is absorbed by
gases called
greenhouse gases.
These gases
in turn re-emit
the energy with some
being sent to space, and
some heading back
to Earth's surface.
This process keeps
the energy in the
lower atmosphere for a
longer period of time,
making the Earth warmer than
it would be otherwise.
This is called the natural
greenhouse effect and keeps
the Earth's average
temperature
around 59 degrees
Fahrenheit.
Eventually, all
energy the Earth
receives from the sun
escapes back
out into space.
If this did not happen,
the Earth would
quickly become
too hot for life
to be present.
