Background: Natural Sources of Radio Waves
By now you and your classmates have become
familiar with the basics of how electromagnetic
radiation transfers energy from one location to
another. You may have even practiced
generating your own waves by oscillating a
current in a wire producing a constantly changing
electric and magnetic field, and thus an EM
wave. Astronomers have long been using their
laboratory observations of these types of
phenomena in order to explain observations that
they are making of the light coming from distant
objects.
When scientists first began to look at the
universe in wavelengths other than the visible
wavelengths, they have been continually
surprised to find many more features than what
were visible to our unaided eye. The detection of naturally occurring radio sources has
greatly improved our understanding of what our universe is made of and how it behaves
in astrophysical systems. By observing incoming radiation in the radio frequency part of
the spectrum (long wavelength), astronomers gain a significant advantage over using
other frequencies. First, radio frequencies have very little disruption as they travel
through our atmosphere. Therefore, we can observe sources from the ground both day
and night and under both cloudy and clear conditions. Secondly, radio frequencies are
less likely to be disrupted by interstellar gases and debris. So again, these frequencies
can travel to us directly from very distant sources without being changed. This is a very
valuable tool to the scientists who are studying the properties of those sources.
In this unit, you will review the fundamental processes of radio frequency emission
reviewing both electromagnetism and spectroscopy. You will have a chance to look at
some real data recorded while observing some sources of radio emissions here in our
milky way galaxy. You will also be able to use that data to infer both the rotational
velocity of the galaxy as well as the total mass of the galaxy. This can be accomplished
by astronomers designing systems to collect the radio waves that have been travelling
for millions of years through our universe and applying fundamental knowledge about
the nature of matter so as to interpret the observations and gain new information from
them.