Tools of the Astronomer • J13
Disappearing Orion: Light Pollution and
Sky Brightness
Activity J13
Grade Level: 4–12
Source: This activity is part of the Dark Skies Rangers Program from the National Optical Astronomy Observatory.
The original activity was written by Natasha Kopsie and Constance Walker at NOAO. The version published here has been revised for classroom use by Andrew Fraknoi at the Astronomical Society of the
Pacific. © copyright 2010 NOAO. Permission to use for any non-profit educational purpose (such as a
classroom or summer camp) is hereby granted.
What’s This Activity About?
Tips and Suggestions
Light pollution is a problem that affects astronomers,
nature lovers, and everyone who values the dark. In this
activity, students measure the amount of light pollution
in their area by seeing what stars are visible in the familiar star pattern of Orion.
• This is a good activity to involve parents and families in
your astronomy unit and to create greater awareness of
the problem of light pollution.
• For more on light pollution see activity M11 (The Night
You Hatched) and resource guide 5.16 (Dark Night
Skies) on The Universe at Your Fingertips disk.
• For more on the magnitude system, see: http://www.
darkskiesawareness.org/DarkSkiesRangers/Dark_
Skies_Rangers_Lessons/How_LightPollution_Affects_
the_Stars.pdf
What Will Students Do?
Students first make a glow-in-the-dark map of how to
find the stars that make up the constellation of Orion.
They also make a red flashlight so they can read outdoors in the dark without disturbing their night vision.
Then they go outside and compare what Orion looks
like to them with charts that allow them to estimate the
amount of light pollution.
What Will Students Learn?
Concepts
Inquiry Skills
Big Ideas
• Light pollution
• Constellations
• Magnitudes
• Observing
• Recording
• Comparing
• Measuring
• Patterns of change
• Models
The Universe at Your Fingertips • Astronomical Society of the Pacific
Page 1
J13 • Disappearing Orion
Tools of the Astronomer
Disappearing Orion: Light Pollution and
Sky Brightness
Constance Walker and Natasha Kopsie
(National Optical Astronomy Observatory)
Andrew Fraknoi
(Astronomical Society of the Pacific)
Part of a suite of activities accompanying the GLOBE-at-Night campaign and the Dark Sky Rangers Program.
Introduction
The lights of human activity are encroaching on the dark
of the night. In many urban areas, even on the clearest
of nights, only a few stars remain visible in the artificial
glow of public, residential, and commercial lighting. A
generation of students is growing up deprived of the
beauty of the night sky. Astronomers call this phenomenon “light pollution” and, because it wastes energy, for
once, the interests of science and the interests of our
economy actually intersect.
Light pollution is a problem because so much of the
human light we produce is not directed downwards,
where we need it, but outward and upward, where it is
completely unnecessary. This costs society a great deal
(in our electricity bills, in the pollution produced in the
course of making the electricity, and in the health effects
of not having darkness at night.) Thus the desire of professional and amateur astronomers to reduce light pollution fits in with the growing movement to conserve
resources and reduce our municipal expenses. Recent
calculations show that something like 10 billion dollars
is wasted annually in the U.S. by lighting up the underbellies of birds and clouds!
An international citizen-science and public awareness campaign called GLOBE at Night has developed a
suite of activities for students and teachers and this is
the central activity in their “citizen science” program to
raise awareness of the pervasiveness of light pollution
in our urban areas. Students look at the constellation
of Orion (the hunter) and measure the amount of light
pollution in their area by checking which of the hunter’s
stars are not visible.
While many teachers encourage (or organize) their
students to participate in the GLOBE at Night cam-
paign each spring (see: http://www.globeatnight.org),
for those whose astronomy unit does not coincide with
the dates of the campaign, we here present the activity as
a stand-alone. Since part of it must be done in the evening, this may be a way to get students’ families involved
in your astronomy unit.
Learning Objectives
Students will be able to:
• Locate the constellation Orion using stellar maps
• Determine the magnitude (brightness) of the faintest
visible stars in their location
• Analyze the data the whole class collected
• Draw conclusions from studying their observations.
Materials Needed:
• 2 different colored tubes of GLOW Tulip brand fabric
paint (or another brand that glows in the dark)
• An ultra-violet light (or a bright regular light)
• 1 transparency (the thicker the better, but make sure
you can still see through them)
• The Orion-at-Your-Fingertips tracing pattern
• A couple of Q-tips
• S omething to write on (clipboard or cardboard) for
each student or student group
• S omething to write with (pencil or pen) for each
student or student group
•M
agnitude charts for Orion and an Observation
Sheet for each student (provided below)
• ( Optional) A letter from the teacher to send home to
parents about this activity
The Universe at Your Fingertips • Astronomical Society of the Pacific
Page 2
J13 • Disappearing Orion
Tools of the Astronomer
• Red light to preserve night vision for each student or
student group (see below for how to make one from a
regular flashlight).
1. The Constellation of Orion
One of the most recognizable constellations in the winter and spring sky is Orion, the great hunter. The figure
of the hunter, with its clear belt of three stars, is visible
in both the Northern and Southern Hemispheres (although Orion seems to be standing on his head if you
are looking at him from “down under.”)
This activity introduces the novice constellation
hunter to a method for spotting the main stars in the
constellation, Orion, the Great Hunter. Simple materials are used to make an outline of the constellation
which, when put under a regular light for 45 minutes,
an LED light for a minute, or an ultraviolet light for 30
seconds, will glow in the dark for 5 to 10 minutes, just
long enough to locate the stars in Orion and imagine the
ancient hunter’s appearance in the sky.
A quick search on the Web can turn up many legends
associated with Orion (from several cultures). Astronomically, Orion contains two bright (and well-known)
stars, above and below the three that make up the belt.
Above the belt, Orion’s left shoulder is marked by the
bright red giant star Betelgeuse (pronounced “Beetel
Juice”), while below, his right foot is indicated by the
blue supergiant star Rigel (pronounced “Rye gel”). These
two are among the brightest stars visible in the sky and
help make Orion relatively easy to spot.
When it’s really dark, you can see a faint “sword” of
stars hanging from Orion’s belt. And when it’s fully dark,
or if you have binoculars or a telescope, there is even a
spot of blood visible on the sword, as if the hunter was
coming back from a fresh kill. This spot of red is the
“Orion Nebula” — a region where we can see new stars
forming from the raw material of the cosmos. If you follow Orion’s belt to the left, it points to the brightest star
in our sky, Sirius. (However, Sirius is in a different constellation, Canis Major, the big dog. In some cultures,
Sirius is considered Orion’s hunting dog.)
2. Making a Finding Chart for Orion
In this step, students make a glow-in-the-dark finder
for the stars that make up the constellation pattern of
Orion.
1) First, place the transparency on top of the Orion
tracing pattern, so the transparency covers the constellation in its entirety.
2) After placing these on the flat surface, trace the
inner constellation pattern with the first color tube of
glow-in-the-dark fabric paint, and follow the pattern
by creating lines and circles on the transparency where
indicated. The inner pattern is the constellation pattern
of stars connected by straight lines and circles. Make
sure that the circles are not filled in with paint. Once
the paint is dry, the transparency will be held at arm’s
length and students should be able to position a star in
each circle.
3) When you’re finished with the inner constellation,
it is time to trace the outer, more imaginative, outline
of the constellation with the second, different-colored
tube of glow-in-the-dark fabric paint.
4) If you blur some lines or make a minor mess while
tracing, quickly try using Q-tips to fix them.
5) When you are finished — DO NOT SKIP THIS —
allow the transparency to dry for AT LEAST 2 hours
(or more if there is high humidity) in a brightly lit area
before attempting to do the activity. (If you have an
LED light or an ultraviolet light, you can expose the
paint to those, as discussed above.)
3. Making a Red Flashlight
When you spend some time in the dark — whether it is
under the stars or in a movie theater — your eye’s pupils open up to be more sensitive to light. This way you
can see dimmer objects, whether it is stars or the spilled
The Universe at Your Fingertips • Astronomical Society of the Pacific
Page 3
J13 • Disappearing Orion
Tools of the Astronomer
popcorn under the seat in front of you. Stargazers who
want to consult a star map or constellation guide usually use a flashlight to see with. But the white beam of
that flashlight can ruin your “night-vision” — your eyes’
adaptation to the dark.
There’s a trick that can help you with this dilemma,
known to both theater ushers and veteran stargazers.
Instead of a white-light flashlight, you can use a redlight one. You could spend money and purchase a special flashlight with a red filter on it, but there is no need.
You can make your own red flashlight easily.
Just cover a flashlight with a red 8 or 12-inch balloon
that has its neck cropped off. Or you can use a singlelayer brown paper bag or red cellophane and secure the
covering with a rubber band to be sure it doesn’t slip
while making the observation. Or you can use a red
handkerchief, neckerchief, T-shirt, stockings, or other
light red cloth.
4. Finding Orion in the Sky
Some teachers organize an evening observing session
for the whole class, inviting parents and other family members to either the school or some pre-arranged
safe observing location. But in most schools, getting
an entire class together in the evening is not practical.
In that case, the rest of the activity becomes a homework assignment, and an opportunity to get students’
families involved. Because going outside and doing star
gazing in many towns and cities should be done only
with adult supervision, you may want to write a letter
to send home with students, explaining the assignment
and suggesting that the whole family join in.
1) After the glow-in-the-dark fabric paint on the
transparency has completely dried and been exposed to
light, you are ready to take the transparency outside to
find Orion.
2) The way to find Orion is to go outside in the evening
in winter or spring and look in the southwest sky if
you are in the northern hemisphere or the northwestern sky if you are in the southern hemisphere. You
are looking for three bright stars close together in an
almost-straight line. These three stars represent Orion’s
belt. The two bright stars to the north are his shoulders
and the two to the south are his feet.
3) A world map where you can click your location to
see a local star chart for Orion can be found at:
http://www.globeatnight.org/observe_finder.html
4) When you have found the general area, hold up the
transparency with the constellation pattern on it at
arm’s length. Match the pattern you have drawn with
the stars in the constellation Orion. You may have to
tilt or turn the transparency to align the pattern correctly with the stars.
5) The constellation pattern has been drawn so the
stars will be visible within the circles drawn on the
transparency itself, allowing the constellation pattern
to be recognizable to even a novice night-sky observer.
6) The transparency with the glow-in-the-dark constellation pattern should glow for approximately 5 to 10
minutes. That should be long enough for everyone in
the group or family to find the belt of Orion and get
oriented in the constellation.
7) If you need to consult any other resources, or see
things in the dark, be sure to use your red flashlight so
The Universe at Your Fingertips • Astronomical Society of the Pacific
Page 4
J13 • Disappearing Orion
Tools of the Astronomer
you don’t ruin your night vision.
Cautions:
a) If it there are clouds in the sky, they might block
crucial parts of Orion and make finding it harder or (if
there is full cloud cover) completely impossible.
b) Students must allow time for their eyes to get
adapted to the dark and be able to see faint stars, especially after having been in a car with headlights on. It is
important to wait at least 10–15 minutes before doing
this activity. A thermos of hot cocoa is really nice during that waiting time.
c) Remember safety first! Students should go outside
only when they are accompanied by an adult and are
properly supervised.
d) Students should always wear suitable clothing for
weather conditions and being outside for a prolonged
period. Also, if there is a chance of traffic coming by,
they should be wearing light or reflective colors.
e) When choosing the darkest area in your location, be
sure the students are not near the edge of a balcony or
natural drop, and that they are not in traffic or in any
other kind of dangerous situation.
5. Understanding the Idea of Magnitudes
Astronomers estimate or measure the brightness of different stars using an old system (created by the ancient
Greeks) called magnitudes. The word comes from the
idea that the Greeks called the brightest stars in the sky
“stars of first magnitude” (meaning the most impressive.) Then stars that were a little less bright were “stars
of second magnitude” and ones even dimmer became
“third magnitude” and so on. The estimates of what
magnitude a star was were made by fallible human beings, but eventually many observers pooled their estimates to come up with a reasonable system (considering
it was all judged by human eyes.) The important thing to
keep in mind is that the larger the magnitude number,
the dimmer the star! So it’s kind of a backwards system
(as opposed to measuring how tall your little brother is
in centimeters, where the larger the number, the larger
your brother.)
Today, astronomers use light-measuring instruments
that are far more accurate than human eyes, and they
measure brightness in much finer gradations than the
crude magnitude system. But among astronomy hobbyists, the use of magnitudes is still very common and this
activity expresses sky brightness in terms of magnitudes
of stars.
Under perfect conditions — perfect vision, no clouds,
no Moon, no human lights — your eyes can see down to
about 6th magnitude and the sky seems filled with stars.
But under realistic conditions, you will see far fewer
stars. The more human light is spilling into the sky, the
fewer stars we can see. We will be measuring the “limiting magnitude” — what is the largest magnitude (the
faintest star) you can see.
6. Measuring the Amount of Light Pollution
Now we want to use the stars in the Orion pattern to
measure the level of light pollution in your area. Students should refer to the pages of the Magnitude Charts
for Orion when following the steps below.
1) Take a good look at Orion after your eyes have had
plenty of time to get adapted to the dark.
2) Get out your magnitude charts, but remember to use
only a red flashlight so you preserve your night vision.
3) Match your nighttime view of the Orion pattern to
one of the magnitude charts: what is the faintest star
can you see
a. Select the chart that most closely resembles what
you are seeing.
b. Estimate the cloud cover in the sky.
4) Fill out the Observation Sheet
5) If possible, students can move to another location
with different light level and make another set of observations
6) If students are doing the observations with their parents, then they might want to write down the address
of their observing location, so that you can plot sky
brightness on a local map.
7. Discussion and Analysis
Whether students do their observations together as a
class (on a night-time field trip or school gathering) or
each student does an observation with his or her family,
be sure that you leave time the next school day for them
The Universe at Your Fingertips • Astronomical Society of the Pacific
Page 5
J13 • Disappearing Orion
Tools of the Astronomer
to compare notes and analyze their results. Was the level
of light pollution the same everywhere the students did
the measurements? Were they surprised by how few of
Orion’s stars they could see?
If students did observations from many different locations, have them enter their magnitude chart number
and location on a map of your area. What makes certain
locations darker than others? If the activity is done during the time that the GLOBE-at-Night campaign is happening (usually in February and/or March), encourage
them to enter their observations in the international tally at http://www.globeatnight.org (you will need to help
them get their latitude and longitude to make an entry.)
Now have them think a bit about the causes of light
pollution. Why does light from our cities spill into the
sky? What could we do to keep light on the ground
(where we need it)? Students could be assigned a research project looking at the causes of light pollution
and suggested solutions.
tive agreement with the National Science Foundation.
GLOBE at Night is hosted by the National Optical
Astronomy Observatory (NOAO) in partnership with
the Environmental Systems Research Institute, Inc.
(ESRI), the GLOBE Program, the Centro de Apoyo
a la Didactica de la Astronomia (CADIAS), and the
International Dark-Sky Association (IDA).
8. Resources for Further Information
about Light Pollution
GLOBE at Night: http://www.globeatnight.org
International Dark-Sky Association:
http://www.darksky.org
Dark Skies Awareness Project:
http://www.darkskiesawareness.org
“A Silent Cry for Dark Skies” in the Astronomical
Society of the Pacific’s Universe in the Classroom
newsletter, Winter 2008 (focuses on the effects
of excess light on animals, and gives some useful
classroom activities and resources):
http://www.astrosociety.org/education/publications/
tnl/74/74.html
Klinkenborg, V. “Our Vanishing Night” in National
Geographic magazine, Nov. 2008: http://ngm.
nationalgeographic.com/2008/11/light-pollution/
klinkenborg-text
Credits
This activity was originally created by Natasha Kopsie
and Connie Walker at the National Optical Astronomy
Observatory (NOAO) for the GLOBE at Night program.
NOAO is operated by the Association of Universities for
Research in Astronomy Inc. (AURA), under a coopera-
The Universe at Your Fingertips • Astronomical Society of the Pacific
Page 6
Disappearing Orion: Magnitude Charts
The following charts were generated with celestial North straight up.
Please orient this page according to your location.
Magnitude below 1
< 0.50 mag
Hint: You can’t see stars in Orion because
the sky is too bright. The star you see
is Sirius in the constellation Canis Major.
Magnitude 2
< 2.50 mag
Hint: You can see two stars in Orion’s belt.
The Universe at Your Fingertips • Astronomical Society of the Pacific
Magnitude 1
< 1.50 mag
Hint: You can only see a couple of the
brightest stars in Orion.
Magnitude 3
< 3.50 mag
Hint: You can see three stars in Orion’s belt.
Page 7
Disappearing: Magnitude Charts
(page 2)
The following charts were generated with celestial North straight up.
Please orient this page according to your location.
Magnitude 4
< 4.50 mag
Hint: You can see four stars in Orion’s belt.
Magnitude 6
< 6.50 mag
Hint: You can see many stars in Orion’s belt,
and his sword is clearly visible.
The Universe at Your Fingertips • Astronomical Society of the Pacific
Magnitude 5
< 5.50 mag
Hint: You can see six stars in Orion’s belt,
and also you can easily find his sword.
Magnitude 7
< 7.50 mag
Hint: You can’t count that many stars!
Page 8
Disappearing Orion: Observation Sheet
Date: ___________________
Your Name: ____________________________________
Observation Time: ____:____ PM local time (HH:MM)
Country: ____________________________
Location: _________________________________________
_________________________________________
_________________________________________
Comments on location: (e.g. There is one street light within 50 m that is shielded from my view.)
Match your nighttime sky to one of our magnitude charts :
< 0.50 mag
< 1.50 mag
Magnitude 2 Chart
Magnitude 1 Chart
S tars in Orion
not visible
< 4.50 mag
Magnitude 4 Chart
< 3.50 mag
< 2.50 mag
< 5.50 mag
Magnitude 3 Chart
< 7.50 mag
< 6.50 mag
Magnitude 6 Chart
Magnitude 5 Chart
Magnitude 7 Chart
Estimate the cloud cover in the sky:
Clear
Clouds cover ¼ of sky
Clouds cover ½ of sky
Clouds cover > ½ of sky
Comments on sky conditions: (e.g. a little haze to the north)
The Universe at Your Fingertips • Astronomical Society of the Pacific
Page 9
Disappearing Orion
Orion,
The Great Hunter
Orion tracing pattern
The Universe at Your Fingertips • Astronomical Society of the Pacific
Page 10