Download Inside the Rainbow

Inside the Rainbow
Astronomy is an unusual science. Astronomers can’t work with stars and planets in a laboratory
the way chemists or biologists can work with the subjects of their study. And yet, astronomers
can tell us what a star is made of and how hot it is, just by looking at it. Have you ever
wondered how they know these things?
It’s All About Light
Most of what we know about objects in space comes from the light they emit, reflect, or absorb.
The branch of science that analyzes the properties of light is known as spectroscopy.
Spectroscopy uses a common principle of light that was first discovered by Isaac Newton. He
was the first to realize that white light is composed of all the different colors. He was the first
person to pass sunlight through a prism to produce a rainbow, which he called a “spectrum”.
To Newton, the spectrum appeared to be continuous, blending smoothly from one color to the
next.
Continuous Spectra
Other scientists followed in Newton’s footsteps to add to what was known about light and our
sun. They discovered that a continuous spectrum containing all of the colors of the rainbow
would be produced by any incandescent body, not just the sun. “Incandescent” means the
substance is so hot it glows- like a piece of hot iron or the filament in a toaster or light bulb.
Fraunhofer Lines
Later, a scientist named Joseph Van Fraunhofer discovered that if you pass the light from a
glowing object through a special lens (a spectrometer), you will get a rainbow or spectrum that
has tiny amounts of some of the colors missing. Instead of a complete rainbow, you’ll see
places with tiny black spaces or lines where some of the colors are missing. This is called a
“black line spectrum”. He showed that our sun had a distinct black line spectrum. Soon,
astronomers began studying other stars to see what their black line spectra (plural of spectrum)
would look like. Some looked like our sun’s spectrum, but others had a different pattern of lines.
Did these lines carry information concerning the star’s make-up?
Elemental Fingerprints
Finally, two scientists figured out what the black lines meant. Gustav Kirchhoff and Robert
Wilhelm Bunsen, working together in a laboratory, held various elements in the flame of a
Bunsen burner. When the element was heated to the point that it glowed, they used a prism to
separate the light it emitted into a spectrum. They discovered that each element has its own
unique set of lines. For example, if a sample of calcium is heated until it glows and the light is
passed through a spectrometer, it will have a certain pattern of black lines on its spectrum. But if
helium is heated until it glows, it will have a different pattern of black lines. Over the years,
scientists have learned the patterns for many different substances. If you just show them a
black line spectrum, they can tell you what substance is glowing. This is true even if the light is
coming from millions of miles away, like from a star.
Now you know how scientists figured out what stars are made of! They analyzed the black line
spectra made from the light of the stars. This process is called “spectral analysis”.
Spectral Analysis
Activity:
You will be provided with a card that has several black line spectra on it. Four substances have
been identified for you. Now that you can see the patterns for these substances, you can use
that information to do spectral analysis of the sun and three other stars. When you’re done,
you’ll know what they are made of, even though no one has ever been there or landed a probe
on any of them.
Follow the directions carefully. Check off each step as it is completed. Write your answers on
the Student Activity Sheet.
Directions:
1. Your teacher will give you an “Activity Sheet”. Find the edge that says, “hydrogen”. Put that
edge directly below the spectrum of hydrogen on the card that contains the spectra. On the
edge of the activity sheet, put a tiny dot under the very beginning and the very end of the
spectrum. Next, put a tiny dot under each of the black lines in the spectrum. Do this very
carefully and accurately! You now have the pattern for hydrogen.
2. Copy the patterns for helium, sodium, and calcium in the same way. Put each pattern in it’s
place along the edge of your activity sheet. Be sure to put a dot under the beginning, ending,
and each black line of each spectrum.
3. Now, look at the spectrum for the sun. This is really a combination of patterns. It is made of
two or more substances. You will need to check each of the patterns you have copied to see if it
is a part of the combination. Start with hydrogen. Put the edge of your activity sheet with the
hydrogen pattern directly under the sun’s spectrum. Be sure to line up the beginning dot and
ending dot of the pattern with the beginning and ending of the sun’s spectrum. Does the sun
spectrum contain the hydrogen spectrum as one of it’s patterns? (It must line up exactly, or it
does not have hydrogen.) If it does have the pattern, list hydrogen on your activity sheet as one
of the components of the sun. If it does not have the exact pattern, hydrogen is not a
component of the sun.
4. Next, check the sun’s spectrum for helium, sodium, and calcium in the same way that you
checked for sodium. If you find a pattern that matches exactly, that substance is part of the
combination. List it as a component of the sun on your activity sheet.
5. Analyze the spectrum of “Star A.” Do it the same as you did for the sun. List its components
on the activity sheet. Then, do the other unknowns.
6. When you have finished your spectral analysis, answer the questions on your activity sheet.
HYDROGEN PATTERN
Name:________________________
Inside the Rainbow
Student Activity Sheet
The directions for this activity are on a separate paper. This paper is for you to use for copying
the patterns in the spectra along the edges and for writing your answers. As you find
substances that are components of the sun or one of the three unknowns, list them below.
____________________________________________________________________________
Star A contains the following substance(s):
HELIUM PATTERN
According to my spectral analysis, the sun contains the following substance(s):
____________________________________________________________________________
Star B contains the following substance(s):
____________________________________________________________________________
Star C contains the following substance(s):
____________________________________________________________________________
Summing Up: When you have completed your spectral analysis of the sun and other
unknowns, fill in the blanks below.
Most of what we know about objects in space comes from the light they ____________,
_________________ ___________________. A prism can split white light into a rainbow,
which can also be called a ____________________.
A ________________ ________________, containing all of the colors of the rainbow,
will be produced by any glowing substance. If you pass the light from a glowing substance
through a special lens called a ____________________ you will see tiny black lines or spaces
where some colors are missing. These are called _______ _______ _____________. These
are like a “fingerprint” because different substances have different _____________ of black
lines. Therefore, these can be used to identify the substance through a process known as
_________ _______________. Scientists use this process to identify what substances make
up stars even though they have never been to a star to collect the data in person!
CALCIUM PATTERN
SODIUM PATTERN
_____________, or ______________________. White light is composed of all the
After your answers have been shared and discussed together in class, use the information from
this activity to answer the following questions. Use complete sentences, of course!
1. Name three ways that stars are classified.
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
2. How did the following scientists contribute to the understanding of stars:
Sir Isaac Newton: ________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
Joseph Van Fraunhofer: ___________________________________________________
____________________________________________________________________________
____________________________________________________________________________
Kirchhoff and Bunsen: ____________________________________________________
____________________________________________________________________________
____________________________________________________________________________
3. Name two new types of technology that helped scientists as they worked to discover
information about stars? _______________________________________________________
4. Explain what a “sprectral analysis” is: __________________________________________
____________________________________________________________________________
____________________________________________________________________________