disappearing orion: light pollution and sky brightness - globe at night · 2012-02-09 ·...

The Universe at Your Fingertips • Astronomical Society of the Pacific

Tools of the Astronomer • J13

What’s This Activity About?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 famil-iar star pattern of Orion.

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 out-doors 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.

Tips and Suggestions• 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

Disappearing Orion: Light Pollution and Sky BrightnessActivity 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 pub-lished 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.

Concepts• Light pollution• Constellations• Magnitudes

Inquiry Skills• Observing• Recording• Comparing• Measuring

Big Ideas• Patterns of change• Models

What Will Students Learn?

http://www.darkskiesawareness.org/DarkSkiesRangers/Dark_Skies_Rangers_Lessons/How_LightPollution_Affects_the_Stars.pdf





Tools of the Astronomer J13 • Disappearing Orion

Disappearing Orion: Light Pollution and Sky BrightnessConstance 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 phenom-enon “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 pro-fessional and amateur astronomers to reduce light pol-lution 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 under-bellies of birds and clouds!

An international citizen-science and public aware-ness 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 eve-ning, this may be a way to get students’ families involved in your astronomy unit.

Learning ObjectivesStudents 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

• Something to write on (clipboard or cardboard) for each student or student group

• Something to write with (pencil or pen) for each student or student group

• Magnitude 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

http://www.globeatnight.org



• 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 OrionOne of the most recognizable constellations in the win-ter 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 (al-though 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 mate-rials 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). Astro-nomically, 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 fol-low Orion’s belt to the left, it points to the brightest star in our sky, Sirius. (However, Sirius is in a different con-stellation, Canis Major, the big dog. In some cultures, Sirius is considered Orion’s hunting dog.)

2. Making a Finding Chart for OrionIn 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 constel-lation 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 FlashlightWhen you spend some time in the dark — whether it is under the stars or in a movie theater — your eye’s pu-pils open up to be more sensitive to light. This way you can see dimmer objects, whether it is stars or the spilled



popcorn under the seat in front of you. Stargazers who want to consult a star map or constellation guide usu-ally 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 red-light one. You could spend money and purchase a spe-cial 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 single-layer 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 SkySome teachers organize an evening observing session

for the whole class, inviting parents and other fam-ily 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 home-work 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 northwest-ern 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 cor-rectly 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 constel-lation 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

http://www.globeatnight.org/observe_finder.html



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, espe-cially 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 dur-ing 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 MagnitudesAstronomers estimate or measure the brightness of dif-ferent 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 impres-sive.) 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 be-ings, but eventually many observers pooled their esti-mates 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 hobby-ists, 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 “limit-ing magnitude” — what is the largest magnitude (the faintest star) you can see.

6. Measuring the Amount of Light PollutionNow we want to use the stars in the Orion pattern to measure the level of light pollution in your area. Stu-dents 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 obser-vations

6) If students are doing the observations with their par-ents, 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 AnalysisWhether 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



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 lo-cations, 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 dur-ing the time that the GLOBE-at-Night campaign is hap-pening (usually in February and/or March), encourage them to enter their observations in the international tal-ly 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 re-search project looking at the causes of light pollution and suggested solutions.

8. Resources for Further Information about Light Pollution

GLOBE at Night: http://www.globeatnight.orgInternational Dark-Sky Association:

http://www.darksky.orgDark 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

CreditsThis 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-

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).



http://www.darksky.org

http://www.darkskiesawareness.org

http://www.astrosociety.org/education/publications/tnl/74/74.html

http://www.astrosociety.org/education/publications/tnl/74/74.html

http://ngm.nationalgeographic.com/2008/11/light-pollution/klinkenborg-text




< 3.50 mag< 2.50 mag

< 1.50 mag

The following charts were generated with celestial North straight up. Please orient this page according to your location.

< 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.

Hint: You can only see a couple of the brightest stars in Orion.

Hint: You can see two stars in Orion’s belt. Hint: You can see three stars in Orion’s belt.

Disappearing Orion: Magnitude Charts

Magnitude below 1

Magnitude 2

Magnitude 1

Magnitude 3


< 5.50 mag

< 6.50 mag < 7.50 mag

< 4.50 mag

Hint: You can see four stars in Orion’s belt. Hint: You can see six stars in Orion’s belt, and also you can easily find his sword.

Hint: You can see many stars in Orion’s belt, and his sword is clearly visible.

Hint: You can’t count that many stars!

The following charts were generated with celestial North straight up. Please orient this page according to your location.

Disappearing: Magnitude Charts(page 2)

Magnitude 4

Magnitude 6

Magnitude 5

Magnitude 7


Disappearing Orion: Observation Sheet

Date: ___________________

Observation Time: ____:____ PM local time (HH:MM)

Comments on location: (e.g. There is one street light within 50 m that is shielded from my view.)

Your Name: ____________________________________

Country: ____________________________

Match your nighttime sky to one of our magnitude charts :

Stars in Orion not visible

Magnitude 1 Chart

< 1.50 mag

Magnitude 2 Chart< 2.50 mag

Magnitude 3 Chart

< 3.50 mag


Magnitude 5 Chart

< 5.50 mag


Magnitude 7 Chart

< 7.50 mag

< 0.50 mag

Comments on sky conditions: (e.g. a little haze to the north)

Estimate the cloud cover in the sky:

Clear Clouds cover ¼ of sky Clouds cover ½ of sky Clouds cover > ½ of sky

Location: _________________________________________

_________________________________________

_________________________________________


Orion tracing pattern

Orion,The Great Hunter

Disappearing Orion

disappearing orion: light pollution and sky brightness - globe at night · 2012-02-09 ·...

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