Transcript Simultaneous Multiple Wavelength Astronomical Observation

Simultaneous Multiple
Wavelength Astronomical
Observation
A Short Quiz
infrared
X-ray
optical
ultraviolet
radio wave
Electromagnetic Waves
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All EM waves travel at the speed of light of
approximately 3x108ms-1 in vacuum.
Different EM waves have different wavelengths and
hence different frequencies.
eg. Red light : wavelength of about 700 nm (nm,
nanometer or 10-9 m).
Blue light : wavelength of about 400 nm.
Radio waves : wavelength ranges from several
centimeters to several meters.
X-rays : wavelengths of about 10-10m.
Light sensitive cells in our retina are only sensitive to EM
waves in a small wavelength window between about 400
nm to 700 nm, it is known as “the optical window”.
Can we investigate astronomical
objects with EM waves spectrum?
All objects are continuously emitting and
absorbing EM radiation. The same object
looks so different at different wavelengths
simply because the object emits, reflects
or absorbs light differently at different
wavelengths.
 In an astronomical object, many different
physical processes are going on. These
processes may lead to production of “light”
at different wavelengths.
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Spectrum of a hot object, such as the surface of our
Sun, depends on its temperature.
A hot iron bar at 3000 K appears dull red.
A 6000 K object such as the surface of our Sun
emits most of its radiation in the form of yellow light.
The hotter the object, the emitted radiation will be of
higher frequency.
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Many other factors could also affect the emission
and absorption of EM waves.
For example, electrical charges moving under the
influence of a strong magnetic field may lead to
the emission of radio waves.
Since most astronomical objects are so far away
from us, it is difficult, if not impossible, to make
measurements on the objects by actually taking
samples from the object.
Therefore, analyzing their EM waves spectrum is
by far the most important way of investigating
distant objects.
Simultaneous Multiple Wavelength
Astronomical Observation
It is a technique which observe an object
in different windows of wavelengths at the
same time.
 Astronomers are able to deduce the
sequence of physical processes or events
in or near the astronomical object. Thus,
they put themselves in a better position to
infer the behaviour of the observed object
and the underlying physics.
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Gamma-ray Burst
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Gamma-rays are EM waves of wavelengths shorter than
10-12m.
Gamma-ray bursts are sudden bursts of gamma-ray
coming from the sky. It was first discovered in the cold war
era (1960's to mid-80's) by gamma-ray detector satellites.
These bursts are found at a rate of about once every day
and they do not seem to repeat. In other words, it is
seldom to find a direction in the sky that bursts more than
once.
In a gamma-ray burst known as GRB970228 at 28th
February 1997, astronomers confirmed that the bursts are
coming from a cosmological distance.
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