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Project Summary

Difficulty	1
Time required	Short (several days)
Prerequisites	None
Material Availability	Readily available
Cost	Very Low (under $20)
Safety	Need a parent to drive to different locations at night, use safety measures when in dark areas.

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Objective

In this experiment you will investigate how the number of visible stars in the night sky can change from place to place because of light pollution.

Introduction

If you live in a big city or urban area it is hard to see many stars at night. In most urban areas only the most brilliant stars, planets and the moon can be seen. This is because of something called light pollution which is the accumulation of background light from homes, automobiles, streetlights and any other source of light in an urban area. This accumulation of background lighting can make it difficult to see the stars at night.

Light pollution is a problem for many urban observatories. As the new development of homes and cities comes closer and closer, urban observatories experience more light pollution. This is why the world's best observatories are located in remote areas, like the Mauna Loa Observatory in Hawaii. It is located in the middle of the vast Pacific Ocean, protecting the observatory from encroaching development and light pollution.

How much light pollution do you have in your backyard? Can you find the best places to view stars in your area? You can find out by conducting an experiment to measure the visibility of stars at different locations.

Terms, Concepts and Questions to Start Background Research

To do this type of experiment you should know what the following terms mean. Have an adult help you search the Internet, or take you to your local library to find out more!

• stars
• planets
• moon
• brilliance
• light pollution
• observatory

Questions

• How many stars can I see from my area?
• Is my area a good location for making astronomical observations?
• Are there other areas near my house that are better locations for star gazing?
• Which places are the best locations for viewing stars?

Bibliography

• Weinrich, Dave. "Counting Stars." Mangilao, Guam: UOG Planetarium. [1/29/06]
  http://www.guam.net/planet/starcount.html
• Gardner, R. and Webster, D. 1987. Science in Your Backyard. New York, NY: Simon & Schuster, Inc.
• Bonnet, R.L. and Keen, G.D. 1992. Space and Astronomy: 49 Science Fair Projects NewYork, NY: McGraw-Hill Inc.
• Asimov, Isaac. 1990. Library of the Universe: Projects in Astronomy. Milwaukee, WI: Gareth Steven's Inc.

Materials and Equipment

• cardboard star counter (a toilet paper tube)
• flashlight
• notebook
• pencil
• a clear night without clouds, fog or a full moon
• a parent to drive you around at night
• three to five different locations for star gazing, some you think will be good and some you think will be bad: your backyard, a city park, downtown , a busy street corner, the outskirts of town, the countryside, the mountains, near an observatory, campground, etc...

Experimental Procedure

1. First, decide with your parents where you will go and choose the location of your test sites. You may want to provide a map of the location of your test sites for your poster. You can make and print a map with your computer by using Google Maps (maps.google.com).
2. Prepare your notebook with a data table for your observations. You will need a data table for each site, including space to write a description for each location and to perform any calculations:

   Location:
   Description:
   Star Counts:
   Sum of Counts:		Average Count:				Total Visible Stars:

3. You will need to pack your bag of supplies since you will be conducting this experiment in the field. Bring your cardboard star counter (toilet paper tube), a notebook, a pencil and a flashlight.
4. On a night when the sky is clear and there is not a full moon, have a parent drive you to your different test sites with your field equipment.
5. At each test site walk to a safe area that is clear, and not covered by trees for example. Write down a description of the site in your notebook.
6. Turn off your flashlight (if you have it on) and allow your eyes to adjust to the light for a few minutes.
7. Hold your counting tube up to your eyes and count all of the stars you see through the tube, being careful not to count any star twice. Write the number in your data table.
8. Repeat nine more times, moving your counting tube slightly to a new view of the sky each time. Write each number in your notebook. You should have ten different counts for each of your test sites.
9. Add together the ten numbers, and then divide the sum by ten. This number will be the average number of visible stars you can see through the tube in that area. Write this number in the data table.
10. Next, calculate the total number of stars in the sky. When using a toilet paper roll to calculate the number of stars in the night sky, the number of stars you see in the tube is equal to a fraction of the total number of stars in the sky. To calculate the total number of stars in the sky, multiply your average by 104. Write this number in your data table. For an explanation of how this number was derived, see Counting Stars by Dave Weinrich.
11. Drive to your next location and repeat steps 4–9 for each test site.
12. Make a graph and analyze your data. Which locations had the most visible stars? The least? Look back at your description of each site and think about why each site was better or worse than the others. Do you notice any trends?

Variations

• Another way to measure light is to use a light meter. A light meter will give a reading of the amount of light present. You can buy a light meter, or you may have one as an option in your camera. Take light readings at night from several of your test sites. Do the changes in light values correlate with the numbers of visible stars in each area? Can you use a light meter to measure urban light pollution?
• Other types of atmospheric pollution can interfere with astronomic observations as well. Do air pollution and smog effect the visibility of stars? Use your local newspaper to find the daily smog or air quality report for your area. Count the stars on a high, medium and low smog day to compare.
• Another source of light that can interfere with star gazing is light from the moon. Try a similar experiment using your star counter to see if the number of visible stars changes with the phases of the moon.

• For more science project ideas in this area of science, see Astronomy Project Ideas.

Credits

Sara Agee, Ph.D., Science Buddies

Last edit date: 2006-02-14 18:58:20

Career Focus

If you like this project, you might want to think about career opportunities in Astronomy.

Astronomers think big! They want to understand the entire universe—the nature of the Sun, Moon, planets, stars, galaxies, and everything in between. An astronomer's work can be pure science—gathering and analyzing data from instruments and creating theories about the nature of cosmic objects—or the work can be applied to practical problems in space flight and navigation, or satellite communications. Learn more about this career: Astronomer.