Name ________________
How Light Is Used To Understand Stars
Scientists use tools to help them understand the universe, galaxies, stars
and planets. A major tool used to gather information about these objects is
called a spectroscope. Spectroscopes help scientists determine the
composition, temperature, motion, and density of objects made up of hot
gases like STARS. A spectroscope consists of a prism that can organize the
wavelengths of light coming from an object into a spectrum based on their
energy. Sunlight can be broken up into a rainbow because the prism breaks
the light into all of its separate colors based on wavelength.
Stars are made up mostly of hydrogen and some helium, oxygen, carbon,
nitrogen, neon and other gases. When scientists looked at the light coming
off of just one element, hydrogen for instance, they didn’t see the whole
rainbow. Instead they just got bright lines of certain colors. That would
mean the element was only emitting waves of certain frequencies. Each
element has a different atomic structure, causing it to produce a different
set of wavelengths. It’s the actions of the electrons (tiny particles that
surround the nucleus) jumping between different orbits that produces a
unique spectrum, almost like a chemical fingerprint that can be used to
identify it. Spectroscopes break down the light produced by chemical
elements into specific lines of color – these are called spectral lines. (It
looks like a “barcode”)
SPECTRAL LINES
a spectral line is a bright or dark line found in the spectrum of some radiant
source. Bright lines indicate emission, dark lines indicate absorption. A
bright spectral line represents light emitted at a specific frequency by an
atom or molecule. Scientists can tell the composition of distant stars just
by looking at the spectral lines of the elements.
CONTINUOUS SPECTRUM
A continuous spectrum is a spectrum of emitted light that contains all
wavelengths of the colors that compose white light (all the colors of the
rainbow blended next to each other in a band - red, orange, yellow, green,
blue, indigo, violet, from long to short wavelength).
Bright-Line Emission Spectrum
Specific gases send out light in only certain wavelengths. This is called a
bright line spectrum - bright lines of color on top of a black background
given off by the specific gases in stars. Each element always produces the
same spectrum.
Using the Spectroscope
1. Do not touch the gas emission tubes – they are very hot.
2. Keeping the spectroscope perpendicular to the source, look through the
eyepiece. Align the slit with the light source.
3. When the slit is properly aligned, examine the spectrum through the
spectroscope.
4. The spectrum is displayed on a wavelength scale inside the spectroscope,
to the right of the slit. The numbers on the scale mark hundreds of
nanometers.
When measuring an emission spectrum, record the wavelengths and colors of
the individual lines.
A bright line spectrum with a blue line at about 445 nm, a green line at 525
nm, and a red line at 635 nm.
Directions
Using colored pencils, fill in each box with the spectrum that you observe in
the lab. Be sure to place each color, line, and boundary at the proper unit
from the spectroscope.
│││4│││││││││5│││││││││6│││││││││7││││
Light Bulb
Hydrogen
Helium
Discussion
1. What does the spectroscope do? ______________________________
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2. What did you see when you looked at the white light? ______________
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3. Explain why this is called a Continuous Spectrum. _________________
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4. What other object emits visible light in a continuous spectrum? (Hint:
We see the light as white light until it is separated by wavelength when it
travels into different substances – prism, water) ___________________
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5. What did you see when you looked at the two gases? _______________
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6. Why are there only certain bright lines or spectral lines when you look at
the spectra from different gases? Is this gas emitting light of all
wavelengths? ______________________________________________
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7. Explain how scientists can identify the elements in a star just by looking
at the spectral lines. _________________________________________
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