• Astronomy is a natural science that is the study of celestial
objects (such as moons, planets, stars, nebulae, and galaxies),
the physics, chemistry, mathematics, and evolution of such
objects, and phenomena that originate outside the atmosphere
of Earth, including supernovae explosions, gamma ray bursts,
and cosmic background radiation.
• The object of study is the spectrum of electromagnetic
radiation, including visible light, which radiates from stars and
other hot celestial objects. Spectroscopy can be used to derive
many properties of distant stars and galaxies, such as their
chemical composition, temperature, density, mass, distance,
• The human eye is sensitive to a very small range of
wavelengths called visible light. However, most objects in the
universe radiate at wavelengths that our eyes cannot see.
• Astronomers use telescopes with detection devices that are
sensitive to wavelengths other than visible light; this allows
astronomers to study objects that emit this radiation, otherwise
invisible to us.
• Computer techniques then code the light into arbitrary colors
that we CAN see. The Hubble Space Telescope is able to
measure wavelengths from about 0.1150 to 2 micrometers, a
range that covers more than just visible light.
• These measurements of electromagnetic radiation enable
astronomers to determine certain physical characteristics of
objects, such as their temperature, composition, and velocity.
NASA Infrared Telescope Facility is an example of a telescope
that operates only at near-infrared wavelengths.
• Astronomical spectroscopy began with Isaac Newton's
initial observations of the light of the Sun, dispersed by
a prism. He saw a rainbow of color.
• Just recently, astronomers discovered a distant solar
system, 127 light years away with up to seven planets
orbiting a Sun-like star called HD 10180.
• Like the very first exoplanet 51-Pegusus discovered in
1995, this new system was found using the science of
• Most of the roughly 500 planets so far found orbiting other
stars, were detected by the same method.
• Spectroscopy — the use of light from a distant object to
work out the object is made of — could be the single-most
powerful tool astronomers use, says Professor Fred
Watson from the Australian Astronomical Observatory.
• "You take the light from a star, planet or galaxy and pass it
through a spectroscope, which is a bit like a prism letting
you split the light into its component colours.
• "It lets you see the chemicals being absorbed or emitted
by the light source. From this you can work out all sorts of
things," says Watson.
• Movement : It helps in determine if an object is moving towards or
away from you by the change in frequency of the wavelength. When
something moves towards you it compresses the signal wavelength it
emits, while if it's moving away from you, it stretches that waveform.
• Age of Star : Spectroscopy also tells us the age of a star by looking
at the amount of its matter made up of chemical elements other than
hydrogen and helium.
• Temperature, mass, gravity : fuzziness of the lines, you can work
out the temperature, mass and pressure and hence, surface gravity.
• The speed at which a star rotates will also show up in the spectrum
by smearing of the lines
• Is the possibility that one day spectroscopy may be used to find life
elsewhere in the universe.