Science 9
Unit 5: Space
Name: Danielle Murray
Topic 3 - The Spectroscope:
New Meanings In Light
Spectral Lines
Isaac Newton passed a beam of light through a prism to produce a spectrum of
colors. If you pass the light through a narrow slit before sending it through a
prism (a spectroscope is a device that does this) the spectrum will be in more
detail. Joseph von Fraunhofer used a spectroscope to observe the spectrum
produced by the Sun. He noticed dark lines, called spectral lines, but didn’t
know what they meant. He found these spectral lines throughout the solar
system.
Spectroscopy: The Science of Colour
The significance of the spectral lines was discovered about 50 years later when
Kirschoff and Bunsen, two chemists used a spectroscope to observe various
chemicals when they were heated. They found some of the lines missing in some
of the chemicals. Each particular element had its own unique spectral lines. This
led to the science of spectroscopy – the study of spectra, as a part of chemistry.
They found that there were three types of spectra.
Spectroscopy for Astronomers
Astronomers refract the light from distant stars to determine what the star is
made of. Stars have dark bands in distinct sequences and thicknesses on their
spectra. Each element that is present in the star creates its own black-line
‘fingerprint’.
The spectra of the star are then compared to known spectra of elements to
determine the star’s composition. This is called spectral analysis. A spectrometer
is used to do this. By attaching spectroscopes to their telescopes, astronomers are
able to observe a star’s spectra, but because the distant stars are much dimmer
than our Sun, only some of the elements in the spectra can be identified. Those
that cannot be identified remain as
inferences, based on what astronomers
know about certain types of stars.
The Doppler Effect
A change in the pitch (frequency) of sound waves because they are stretched or
squeezed is known as the Doppler effect. Changes in the sound waves can be
measured to determine how fast and in what direction a light-emitting object is
moving. The position of the dark bands is what shifts in the light waves of a
moving star.
The spectrum of an approaching star shows the
dark bands shifting to the blue end of the
spectrum, whereas, the shift is to the red part of
the spectrum if a star is moving away from the
Earth.
Remember:
Blue moving towards (cold you can touch)
Red moving away (HOT stay away)
The amount of shift indicates the speed at which the star is approaching or
moving away. There are also practical applications that use the Doppler effect.
Law enforcement officers detect the speed of an approaching vehicle by using
a radar gun, which sends out a radio signal and receives one back from the
vehicle. To determine the speed of the vehicle, the hand-held device records
the difference in the outgoing wavelength and incoming wavelength.
An Amazing Tool
The spectroscope is an amazing tool. Its application to astronomy has helped
astronomers determine the composition of distant stars
3 classes of Spectrum



Continuous Spectrum- has all colors and no black streaks
Emission lines- mostly dark except for some little streaks of light
Absorption lines- Opposite of emission lines with lots of color and black
streaks
High density hot matter- diffraction grating- continuous spectrum
Hot gas- diffraction grating- Emission Spectrum
Light bulb- cold gas- diffraction grating- Absorption spectrum
Red shift- Moving away from you
Blue shift- Coming close to you
Normal- at rest
Vocabulary:
Spectrum- Colors produced by a beam of light going through a prism.
Spectral lines- dark lines or bright lines observed in the spectra of stars.
Spectroscopy- The study of spectra spectrum produced when a beam of light is
passed through a prism.
Diffraction grating- A device made of thousands of closely spaced slits through
which light is passed in order to produce a spectrum.
Spectral analysis- the study of spectra
Doppler effect- The phenomenon that the observed frequency of a wave changes
if the source of the wave and the observer are moving toward or away from one
another.
Red shifted- When spectral lines move toward the longer-wavelength part (red
end) of the spectrum.
Blue shifted- The spectrum of an approaching star shows the dark bands
shifting to the blue end of the spectrum. Blue moving towards (cold you can
touch), the dark lines in the star’s spectrum shift toward the shorter-wavelength
end of the spectrum- blue shifted.
1. Describe how a spectroscope works.
A spectroscope works- Isaac Newton passed a beam of light through a prism to
produce a spectrum of colors. If you pass the light through a narrow slit before
sending it through a prism (a spectroscope is a device that does this) the
spectrum will be in more detail
2. If you heat a piece of wire until it glows, what type of spectrum should it
produce?
If you heat a piece of wire until it glows, it would produce a continuous
spectrum because if you heat a solid at high pressure the result of the spectra
would have all the colors blending into one.
3. What instrument would you use to find out what elements are in the
Sun’s atmosphere. How is this done?
You would use a spectrometer- by attaching spectroscopes to their telescopes,
astronomers are able to observe a star’s spectra. Spectral analysis is used to also
figure out what is in the Sun’s atmosphere by seeing if the placement of the dark
lines’ in the solar spectrum is the same as the bright lines made by many
different elements, therefore those elements are in the Sun’s atmosphere. (the
dark lines will appear in the same location as the bright lines)
4. If a star’s light is red shifted what can astronomers conclude about the
movement of that star?
If a star’s light is red shifted astronomers can conclude that the star is moving
away from you.
5. What is the Doppler effect? Give an example of it being used.
The Doppler effect is the change in pitch and is caused by the change in the
sound’s wavelength. For example; the siren on a fire truck, sound waves are
compressed in front of the vehicle as it speeds along having shorter- wavelength
and higher pitch. Behind the vehicle sound waves stretch out, having a longerwavelength and lower pitch.
6. Answer questions # 6 and 7 in the Topic 3 Review questions page 384.
Use the space below…
Analyzing Spectral Patterns
What to Do Analyze the spectra below in order to answer the following questions.
Questions
1. List the chemical elements in:
(a) Mystery Star 1
Helium, Hydrogen
(b) Mystery Star 2
Hydrogen, Helium, Sodium
(c) Mystery Star 3Hydrogen, sodium
1. (a) There is something strange about
Mystery Star 4’s spectrum. What
chemical is in Mystery Star 4?
Hydrogen
(b) What is odd about the spectrum?
Mystery star 1,2,3 have 3 of the
same lines that match up but 4 is
different.