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HOW
ASTRONOMERS USE THE ELECTROMAGNETIC SPECTRUM
The development of instruments to measure wavelengths
of light in all parts of the Electromagnetic
Spectrum  has
contributed immensely to science.
We now know that certain animals snakes)
can "see" infrared light. This allows them
to find prey in the dark because thermal energy is
emitted in the infrared. Scientists have developed
cameras that allow us to "see" infrared light.
Below is an infrared image of an engineer holding a
burning match.
Photo to right: Courtesy of Infrared Information
Processing Center, California Institute of Technology,
Jet Propulsion Laboratory
"False colors" have been used
to indicate temperature. Note the white and deep red
in the flame and the engineer's palm (where his warm
blood vessels are close to the surface of the skin)
and the blue of his cool glasses.
This kind of imaging has been very important
to scientists. These images of the Earth showing ocean
temperatures were taken from a satellite.
Infrared imaging has aided astronomers,
too. These images show the constellation Orion as it
is seen with visible light (left) and with infrared
light (right).
(Photo above: Courtesy of Infrared Information
Processing Center, California Institute of Technology,
Jet Propulsion Laboratory)
The yellow regions in the right image
are hottest and show scientists the hot gasses around stellar
nurseries. The clouds of red are relatively cooler
interstellar gas and dust. Little of this information
is available from visible light.
 Other
animals (like bees) can "see" ultraviolet.
A bee's view of flowers is remarkably different than
ours. The following image shows a flower of a species
of plant pollinated by bees.
 In
many ways this flower is unremarkable. However, a picture
of the same flower taken with film sensitive to ultraviolet
radiation looks very different. The pattern in ultraviolet guides a
bee to pollen and nectar. (Photo's: Courtesy of Nectar
Guides)
Detectors sensitive to ultraviolet light
guide astronomers to new information. Peter Bunclark
took this image of Galaxy M101 in visible light.
 The
image below is another view of Galaxy M101 taken by
the Ultraviolet Imaging Telescope (UIT) onboard the
Space Shuttle Endeavour. UIT is an instrument sensitive
to ultraviolet light. The image has been computer processed
so that the colors represent the intensity of ultraviolet
light.
 This
shows mainly clouds of gas containing newly formed
stars many times more massive than the sun, which glow
strongly in ultraviolet light. The ultraviolet image
shows astronomers much more about new star formation
than the photograph taken in visible light. (Photo:
courtesy of Ultraviolet Imaging Telescope)
The Solar
and Heliospheric Observatory (SOHO) is a project
of international cooperation between the European
Space Agency and NASA. Among its many scientific
contributions, it enhances our knowledge by photographing
the Sun in several wavelengths nearly at the same
time. The following images were taken within 2 hours
of each other. All colors are "false colors" chosen
to help scientists know what wavelength is being
viewed. The brightness corresponds to intensity of
radiation.
 The
Michelson Doppler Imager (MDI) aboard SOHO took the
image below. This image shows the Sun as it looks in
the visible wavelengths. The scale at the bottom relates
color to temperature.
The dark areas are sunspots and the bright
regions are faculae. These are regions of complex
solar activity.
 The
Extreme Ultraviolet Imaging Telescope (EIT) took this
image at an ultraviolet
wavelength of 304Å.
Scientists know that light emitted at
this wavelength is predominantly emitted by helium
that has lost one electron (ionized) at 60,000 to 80,000°C.
Knowing the wavelength of light emitted tells the scientists
something about the temperature, the chemistry and
the layer of the Sun being viewed because helium can
only exist in a particular state and temperature in
specific locations. Notice that the regions of more
intense radiation at 304Å correspond to regions
where sunspots and faculae occur.
 The
following image was also taken by EIT at 171Å.
Light emitted at this wavelength is predominantly emitted
by iron that has lost 8 or 9 electrons that happens
at 1,000,000°C. The features seen here are in the corona.
Compare the areas of most intense radiation at 171Å with
those at 304Å and the pictures taken by MDI.
 The
following image was taken by EIT at 195Å. Light
emitted at this wavelength is predominantly emitted
by iron that has lost 11 electrons at 1,500,000°C.
The features seen here are in the corona. Compare these
areas of most intense radiation with those in the other
images.
 The
following image was taken by EIT at 284Å. Light
emitted at this wavelength is predominantly emitted
by iron that has lost 14 electrons at 2,000,000 to
2,500,000°C. The features seen here are in the
corona. Compare these areas of most intense radiation
with those in the other images.
The last three images show loop structures
in the corona. The presence, structure and dynamics
of these loops give scientists important insights into solar
processes.
People are also familiar with the use
of x-rays to allow us to "see" things that
are not visible. But astronomers use x-rays far differently
than doctors do. An x-ray of a broken bone does not
show us the source of the x-ray. What we see in an
x-ray picture shows different intensities of the x-rays
coming through the object between the emitter and the
film. William Conrad Roentgen discovered x-rays in
1895 and took this 'picture' of the hand of his wife,
Bertha.
 The
bone of her hand and the metal ring blocked x-rays
from the film. You can see a faint outline around the
bone that is the skin and muscle. However, astronomers
look directly at the source of x-rays and create images
of the object emitting the x-ray. The Chandra X-ray
image of Supernova 1987A shows an expanding shell of
hot gas produced by the supernova explosion.
 Photo:
The colors represent different intensities of X-ray
emission, with white being the brightest.
Recent optical observations of SN 1987A
with the Hubble
Space Telescope have revealed gradually brightening
hot spots from a ring of matter that was ejected by
the star thousands of years before it exploded. Chandra's
X-ray image shows the cause for this brightening ring.
A shock wave, traveling at a speed of 4,500 kilometers
per second (10 million miles per hour), is smashing
into portions of the optical ring. The gas in the expanding
shell has a temperature of about 10 million degrees
Celsius, and is visible only with an X-ray telescope.
Closer to home Yohkoh is
looking at the Sun in X-ray. The  image
below is in a lower energy - or soft - x-ray.
Photo: False color image courtesy of Yohkoh. Brightness indicates high intensity
of x-ray. 2001/11719:52
The Soft X-ray Telescope on board the
Yohkoh satellite was designed to study the hottest
part of the Sun's atmosphere (the corona). Because
the corona is so hot (2 million degrees Celsius) it
is best studied by detecting the X-rays it emits. Scientists
are able to compare x-ray data from Yohkoh to images
from SOHO in ultraviolet and visible light. The image
above was taken within a comparable time frame to the
SOHO EIT images shown in the UV section of this page.
Images taken at the same time in different wavelengths
allow scientists to look at different parts of the
Sun. They can then make connections between events
in different parts of the Sun.
The Solar-B satellite,
soon to be launched, will carry a coordinated set of
instruments that will measure the Sun's magnetic field
and simultaneously its ultraviolet and X-ray emissions.
This data will improve our understanding of the Sun's
variability and will contribute to a deeper understanding
of the Sun's influence on life on Earth.
Electromagnetic radiation with wavelengths
longer than infrared include radio waves and microwaves.
We are most familiar with these types of radiation
as carriers of radio or television signals or to heat
our food. However, in 1931 scientists discovered that
radio waves were coming from space and these radio
waves were not carrying an extraterrestrial version
of "I Love Lucy". Instead they were caused
by electrons being accelerated by collisions or interactions
with magnetic fields. Other radio wavelengths come
from the behavior of molecules such as rotations or
vibrations. Scientists are able to use radio emissions
from space to determine the molecular structure and
the surrounding environment of objects and clouds of
dust and gas in space. One of the least understood
of all radio sources are quasars (quasi-stellar
radio source).
The following image shows Galaxy M81  taken
at a wavelength that shows radio emissions from neutral
hydrogen.
The most intense radiation is red and
the least intense is blue. Scientists learn very important
information about the structure and dynamics of clouds
of dust and hydrogen around stars.
Scientists use an extremely powerful
technique to study objects in space. They combine information
from several widely different wavelengths. Click here
for images of the Sun in all the different wavelengths.
Astronomers are also studying our own
galaxy, the Milky Way. Our solar system lies about
two-thirds of the way out away from the center of our
galaxy.  The Multiwavelength
Milky Way shows our galaxy in 10 different wavelengths
representing each major portion of the electromagnetic
spectrum. Since the images show 360º we can see
the entire Milky Way.
Photo Left: Courtesy of Multiwavelength
Milky Way
It is well worth visiting The Multiwavelength
Milky Way web site and seeing each part of the above
poster in detail - or even ordering your own poster!
The development of instruments capable
of extending our 'sight' into all wavelengths of the
electromagnetic spectrum enables scientists to know
so much more about the structure and dynamics of the
universe. Multiwavelength
Astronomy reveals the universe in all of its light.
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