Geoscience Reference
In-Depth Information
The Electromagnetic spectrum
and solar Energy
in the
visible light
part of the spectrum, which ranges from vio-
let with the shortest wavelength of 375 nanometers (nm) to red
with the longest wavelength (740 nm).
You should remember two very important principles about
electromagnetic radiation. The first principle is that an
inverse
relationship exists between the temperature of an object and
the wavelength of the electromagnetic radiation it emits. In
other words, hotter objects emit radiation with shorter wave-
lengths than cooler objects. For example, the Sun has a sur-
face temperature of about 6000°C (11,000°F) and emits energy
as
shortwave radiation
, which includes gamma rays, X-rays,
ultraviolet (UV) radiation, visible light, and near-infrared ra-
diation. The Earth, in contrast, is a much cooler object (~16°C,
61°F) and thus emits
longwave radiation
in the thermal infra-
red part of the spectrum (Figure 4.3). Keep in mind, though, that
the vast majority of energy released by Earth initially originated
at the Sun.
The Electromagnetic spectrum
Radiation is electromagnetic energy that is transmitted in the
form of waves. These waves can be measured in terms of their
length and amplitude, with
wavelength
being the distance
between wave crests, and the term
wave amplitude
referring
to half the height between the wave crest and wave trough
(Figure 4.1). The entire wavelength range of electromagnetic
energy is called the
electromagnetic spectrum
.
Within the electromagnetic spectrum, wavelengths range
from
gamma rays
that are less than a nanometer long (one bil-
lionth or 10
-9
of a meter) to
radio waves
that are tens of meters
in length (Figure 4.2). Humans can see radiation directly only
One wavelength
Longer waves
One wavelength
One wavelength
Amplitude
One wavelength
Crests
Shorter waves
Troughs
Figure 4.1 Relative sizes of electromagnetic waves.
The distance from one crest to the other, or
from one trough to another, is called the wavelength. Wave amplitude refers to half the distance from
the wave crest to the wave trough.
The distance between adjacent wave crests or
Wavelength
shortwave radiation
The portion of the electromagnetic
spectrum that includes gamma rays, X-rays, ultraviolet radia-
tion, visible light, and near-infrared radiation.
wave troughs.
Wave amplitude
The overall height of any given wave as
measured from the wave trough to the wave crest.
longwave radiation
The portion of the electromagnetic
spectrum that includes thermal infrared radiation.
Electromagnetic spectrum
The radiant energy produced by
the Sun that is measured in progressive wavelengths.
