Transcript Spectral_Analysis

Spectral Analysis
Gleaming Information From
The Stars
Somethings wrong?
But How do we know?
We’ve been there!
But what about outer space?
Visible Spectrum
While passing through a prism, white light
splits into its component colors, spanning
red to violet in the visible part of the
electromagnetic spectrum.
Spectral Analysis
Astronomers can analyse electromagnetic radiation
received from space to obtain information about
distant objects
Radiation is analysed with an instrument known as
a spectroscope (or spectrometer) consisting of a
telescope (to capture the radiation), a dispersing
device (to spread it out into a spectrum-usually a
prism or diffraction grating), and a detector.
Emission Spectra
A light bulb emits radiation of all wavelengths
(mostly in the visible range)
Viewed through a spectroscope, the spectrum
of the light from the bulb would show the
familiar rainbow of colors, from red to violet in
a continuous spectrum.
Spectral Lines
Light produced by
excited hydrogen gas
does not consist of all
possible colors but
instead includes only
a few narrow, welldefined emission
lines.
Spectral Lines of Other Elements
Similar experiments on many different
gases show that sometimes the pattern of
lines is fairly simple, sometimes it is very
complex but always it is unique to that
element.
Spectral lines
provided a oneof-a-kind
"fingerprint" of the
substance under
investigation.
ASTRONOMICAL APPLICATIONS
Once astronomers knew that spectral lines were
indicators of chemical composition, they set
about identifying the observed lines in the solar
spectrum (The spectrum given out by the sun).
Almost all the lines in light from extraterrestrial
sources were attributed to known elements,
however, some new lines also appeared in the
solar spectrum.
In 1868, astronomers realised that those lines
must correspond to a previously unknown
element. It was given the name helium, after the
Greek word helios, meaning "Sun." Only in
1895, almost three decades after its detection in
sunlight, was helium discovered on Earth.
Analysing the Spectra from Stars
By analysing the
spectra of a star or
nebula, it will show
many
superimposed lines
from the different
atoms that make up
the star or nebula’s
composition.
This picture shows
the actual spectrum
observed from the
hot gases in the
Omega nebula
Stellar Spectra
This image shows
spectra from
several different
types of stars.
The image can be
in black and white
because it is the
relative position of
the lines that
identify the
elements present.
Learning From Afar
Virtually all we know about planets, stars, and
galaxies is gleaned from studies of the light we
receive from them.
After using the spectroscopes you should be
able to identify:
– The difference between Continuous and Emission
Spectra
– Spectral lines from excited gases using reference
books and tables
– The chemical composition of several ‘cosmic bodies’
from their emission spectra