Name:________________________________________ Date:______________________ Block:__________
WHAT’S IN A COLOR? – SPECTRAL ANALYSIS LAB
Background:
Our sun is a star. Everyone knows this now. But the early scientists did not believe this. There was
no proof! The key to the proof came in 1850 with the invention of the spectroscope. When light
passes through a prism, it separates into bands of color known as a spectrum. By putting a narrow
slit in front of a prism you create a spectroscope.
A spectroscope identifies elements by the colors they emit. Every substance gives off light when it
becomes hot enough. Every element gives off its own unique pattern of lines in the spectrum in
specific locations. We call these lines a spectrum. A spectrum is like a fingerprint. No two people
have the same fingerprints. And, no two elements have the same spectrum. But the spectrum is
always the same for a particular element.
There are several types of spectra. A continuous spectrum shows a rainbow of colors that blend into
each other without interruption. Glowing solids or liquids emits a continuous spectrum. The dark line
or absorption spectrum is produced when radiation from underlying layers of a star passes through
cooler outer layers. These appear as if it is a continuous spectrum broken up by dark lines. The
bright line or emission spectrum appears as bright lines with dark spaces between them. Hot gases
at low pressure cause these.
The spectroscope does more than identify the chemical make-up of the stars. The spectroscope also
tells us: the temperature of a star, how fast a star is moving and in which direction.
Purpose:
To use a spectroscope to examine different types of spectra and to relate these results to astronomy.
Procedures:
Sketch the spectra for each of the samples that you are shown. Take care to make the drawings as
accurately as you can.
Analysis Questions:
1. Which sources emitted a continuous spectrum? Explain why.
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2. Which sources emitted an emission spectrum? Explain why.
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3. Were any of the spectra for the elements the same? Explain why.
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4. Why didn’t any of the sources emit an absorption spectrum?
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Use the diagram below to answer the following questions.
HOT, DENSE
ENERGY SOURCE
CONTINUOUS
SPECTRUM
HOT, LOW
DENSITY CLOUD
OF GAS
EMISSION
SPECTRUM
HOT, DENSE
ENERGY SOURCE
COOL, LOW
DENSITY CLOUD OF
GAS
ABSORPTION
SPECTRUM
5. What type of spectrum is produced when the light emitted directly from a hot, dense object passes
through a prism?
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6. What type of spectrum is produced when the light emitted directly from a hot, low density cloud of
gas passes through a prism?
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7. There are dark lines in the absorption spectrum that represent missing light. What happened to
this light that is missing in the absorption line spectrum?
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8. Stars like our Sun have low density, gaseous atmospheres surrounding their hot, dense cores. If
you were looking at the spectrum of light coming from the Sun (or any star), which of the three
types of spectra would be observed? Explain your reasoning.
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9. If a star existed that was only a hot, dense core and did NOT have a low density atmosphere
surrounding it, what type of spectrum would you expect this particular star to emit? Why?
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10. Of all the sources you viewed, which was your favorite and why?
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