Space InfraRed Telescope Facility
Space Infrared Telescope Facility (SIRTF):
The Herschel Experiment
Dr. Michelle Thaller
thaller@ipac.caltech.edu
SIRTF Science Center
California Institute of
Technology
sirtf.caltech.edu
Dr. Denise Smith
Dan McCallister
Origins Education Forum
Space Telescope Science
Institute
Space InfraRed Telescope Facility
The Origins Program
Origins:
Where did we come from?
Are we alone?
Space Infrared Telescope Facility
 Exploring the universe in the
infrared
 Planned launch: December 2002
 Expected lifetime: 5 years
Space InfraRed Telescope Facility
The Discovery of Invisible Light
A Fortunate Accident
In 1800, while placing thermometers
in each color of the solar spectrum,
Herschel places his “control”
thermometer just outside the red end
of the spectrum.
Result: the thermometer outside the
visible spectrum registered the
highest temperature!
The first detection of invisible
light, which Herschel called
infrared (“beneath red”) light.
Space InfraRed Telescope Facility
The Herschel Experiment:
A Classroom Activity
Objective: To perform a version of
the experiment of 1800, in which a
form of radiation other than visible
light was discovered by the famous
astronomer Sir Frederick William
Herschel.
Target Audience: Grades 7-9,
easily extended to higher grades
(10-12)
Space InfraRed Telescope Facility
Herschel Experiment Set-Up
1. Place a sheet of white paper
inside a cardboard box
2. Tape three thermometers
together and place inside box
3. Cut a small notch in the top of
the box and position a small
glass prism so that the
spectrum is projected inside
the box
4. Arrange the thermometers so
Do not look directly at
the Sun.
that one is just outside the red
end of the spectrum, with no
visible light falling on it
Space InfraRed Telescope Facility
Results
The thermometers will
register differences almost
immediately.
After approx. 10
minutes, the
thermometers show a
10 degree difference:
The highest temperature is found outside the
visible spectrum, where infrared light is falling on
the thermometers.
Space InfraRed Telescope Facility
Team Roles
The Herschel Experiment can be done in groups of 2 to 4. Team
members can be assigned the following roles:




Box-keeper – makes sure the thermometers are positioned properly
and holds box if necessary
Timekeeper – announces times for temperature measurements
Measurer – reads the temperatures of the thermometers
Recorder – records the temperatures on the observation chart
Space InfraRed Telescope Facility
Today’s Goals
1. Adjust the prism in the notch until a broad spectrum is achieved.
2. Place thermometers in the blue, the yellow, and next to the red
portions of the spectrum for 30 to 60 seconds, until a temperature
difference is observed.
 If 3 thermometers will not fit in the spectrum, place one
thermometer in the yellow and one thermometer next to the
red portion of the spectrum. Optional: Keep the 3rd
thermometer in a shaded area of the box, as a control.
3. Using the Herschel Experiment Worksheet, continue taking data
for 4 to 5 minutes.
Space InfraRed Telescope Facility
Workshop Discussion
Useful discussion questions for the workshop (and classroom) setting:

Did you observe a temperature rise in the infrared?

Did you encounter any difficulties while doing the experiment? If so,
how did you solve them?

Consider recording the final thermometer readings and elapsed
time for each group. Comparing results can lead to an interesting
discussion of experimental uncertainties.
Space InfraRed Telescope Facility
Additional Questions

Insightful students may wonder why
the blue thermometer doesn’t have
the highest temperature. After all,
doesn’t blue light have more energy
than red light?

The answer lies in what the prism
does to the light. Prisms spread blue
light out, while red light remains
more focused. After passing through
the prism, the energy in the red and
infrared parts of the spectrum is
more concentrated.

A more thorough discussion can be
found on the SIRTF website
(sirtf.caltech.edu).
Space InfraRed Telescope Facility
Helpful Hints
For best results, do
experiment in direct
sunshine, when the Sun
is high (noon). Putting
the prism in the cut notch
provides stability and
easy rotation.
Blacken the bulbs of the thermometers
with black paint. Flat black spray paint
works best, but even a black magic
marker will yield results.
The experiment WILL NOT WORK
without the paint (Herschel sootblackened his thermometers in the
original experiment).
Glass prisms work
much better than
plastic ones (this is
Herschel’s original
prism).
Space InfraRed Telescope Facility
Herschel Experiment Ideas

Makes a great science fair activity:
Space InfraRed Telescope Facility
The Importance of Infrared

How is infrared light used in our
daily lives?

Why would astronomers put a
telescope in space to look at
infrared light?
Space InfraRed Telescope Facility
Infrared Measures Heat
Every object with a temperature above absolute zero radiates in the infrared.
Space InfraRed Telescope Facility
Infrared in Society



Oceanography
Firefighting
Commercial Applications
Space InfraRed Telescope Facility
Infrared Astronomy:
Detecting “Cool Objects”
Finding “brown dwarfs”
helps us measure the
mass of the universe.
Debris disks – signs of
other solar systems?
Space InfraRed Telescope Facility
Infrared Astronomy:
Viewing the “Invisible”
Dust absorbs visible light and re-emits it in the infrared.
Some galaxies emit most of their light in the infrared.
Space InfraRed Telescope Facility
Infrared Astronomy:
Exploring the Early Universe
Just as the pitch of a train
whistle changes as it passes an
observer, the observed
wavelength of light emitted by a
moving object also shifts.
Visible light from very distant objects is shifted to the infrared.
Space InfraRed Telescope Facility
Why a Telescope in Space?
Infrared light is mostly absorbed by our atmosphere.
Space InfraRed Telescope Facility
For More Information…
Michelle Thaller
thaller@ipac.caltech.edu
SIRTF Science Center,
California Institute of Technology
sirtf.caltech.edu
Space Science Education
Resource Directory
Teachspacescience.org
Origins Education Forum
Origins.stsci.edu
Click on “Educator Resources”,
and then select “Curriculum
Support”