ASTRONOMY
THE MESSAGE
A. Light and Electromagnetic waves
How do we know anything about this universe in which we live? After
all, we have barely stepped off the earth. While we have visited the moon
and been in physical contact with the surface of Mars and Venus, it is
doubtful that we will ever physically explore beyond the solar system.
All that we know of the universe we learned from waves and light. Stars
and galaxies all emit light and other electromagnetic waves; in fact all
objects emit waves. From these waves we can figure out much about the objects
that emit them or reflect them.
A wave is a disturbance that travels through space and carries energy.
There are all sorts of waves. Some waves, mechanical waves, such
as sound, earthquakes, or ocean waves, disturb matter, . Others waves are
electrical and magnetic in nature, electromagnetic waves (EM waves).
Light belongs in the latter category. What we see as white light is actually
a family of waves, a spectrum of 7 different colors (Violet,
Indigo ,
Blue,
Green,
Yellow,
Orange
and Red)
that are blended together into white by our eye (the first person to
demonstrate this was Newton). Since Newton's time we have come to realize
that the EM spectrum includes a variety of wavelengths and frequencies
that extend well beyond visible light and range from the longest radio
waves to extremely short gamma rays.
B. The EM spectrum
Shorter Wavelength----->
Increasing Frequency--->
Increasing Energy-------> |
Radio |
Microwave
Radar |
Infrared |
Visible ROYGBIV |
Ultraviolet |
X rays |
Gamma rays |
<-----Longer Wavelength
<--------Decreasing Frequency <--------Decreasing
Energy |
As different as they might appear to us, these waves are all related, they
are all EM waves, differing only in wavelength, frequency and energy. In
space, they all travel at the CONSTANT speed of light, 300,000 km/s or
186,000 mi/s. |