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WHAT IS INFRARED ASTRONOMY?
J. S. Sweitzer
11/22/94
Old, traditional pictures of working astronomers usually show a person viewing
through the eyepiece of a long telescope tube. Or, maybe they took photographs
through the telescopes that could then be printed in books. Today astronomers
have films and electronic devices that extend the range of our ability to
detect light into parts of the spectrum that are invisible to the eye. This
is very important because the planets, stars and galaxies scattered across
our universe send out an entire symphony of light over a wide range of wavelengths.
An astronomer who only studies visible light is like someone who could only
hear one particular note in a Beethoven symphony. Infrared astronomers can
hear a much wider part of the symphony of the Universe. They can detect
what would be analogous to all the notes played in the bass clef.
What determines what type of light an object in space will emit? For
most stars, planets and dust in the Universe the type of light they give
off is determined by the temperature of the object. The Sun's surface
is about 10,000 degrees Fahrenheit and emits most of its energy in the
visible part of the spectrum. Hotter stars emit light at shorter wavelengths
and cooler stars give off most of their light at longer wavelengths. The
infrared light that SPIREX (South Pole Infrared Explorer) observes has
a wavelength of four times that of yellow light. That means that SPIREX
sees the light of objects that are about 1/4 as cool as the Sun or 2,500
degrees Fahrenheit. Other infrared telescopes can see things at far infrared
wavelengths one hundred times longer. These objects are as cold as 25
degrees Fahrenheit.
Cool stars, planets and dust emit light at infrared wavelengths. In
particular, SPIREX is tuned to be able to see objects that are a couple
of thousand to a few thousand degrees. These temperatures are far cooler
than typical stars. Only the coolest stars we know emit at these temperatures.
Stars being born should glow at these wavelengths. Young galaxies are
expected to have billions of such stars. There may also be "missing link"
objects called brown dwarves that are somewhere between the categories
of stars and giant planets. SPIREX even saw the explosions that took place
on Jupiter when pieces of the Shoemaker-Levy 9 struck last July.
Infrared astronomers face two difficult problem that optical astronomers
don't have. Most wavelengths of infrared light have trouble penetrating
Earth's atmosphere. This is primarily because molecules in the air block
the infrared light from space. To make matters even worse, the atmosphere
and even the telescope emit infrared light since they are in the temperature
range of things that give off infrared light. To get around these problems
infrared astronomers fly their telescopes in aircraft and on spacecraft
to get above warm, moist air. On the surface of the Earth, the South Pole
is the coldest and driest site we astronomers can use and therefore the
best location for infrared astronomy on the planet.
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