Areas of Science Astronomy
Time Required Very Short (≤ 1 day)
Prerequisites None
Material Availability Readily available
Cost Very Low (under $20)
Safety No hazards


Do you like to look up into the night sky? There are so many stars, it can be mind boggling! Some ancient people marked time by the changes in star patterns. We still use changes in constellation patterns to mark astronomical time. Do constellations change more in one hour, one day, one month, or one year?


In this experiment you will investigate how the constellations change in the night sky over different periods of time.

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Sara Agee, Ph.D., Science Buddies

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Science Buddies Staff. "Changing Constellations." Science Buddies, 12 Jan. 2020, Accessed 11 Apr. 2021.

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Last edit date: 2020-01-12


The telling of time is an ancient art, and different ways of marking time have been used by people of different cultures over the ages. Before the introduction of modern standard time, people had to use astronomical features to mark time, mainly the sun, moon and stars. Different calendars were created by different cultures who marked time by using different methods. Here are just a few:
  • Gregorian Calendar: This calendar marks time by the rising and setting of the sun, called solar time. It was introduced in 1582 as a reform to the Julian calendar of 45 B.C. that had been initiated by the Romans. Before Gregorian and Julian time, people had been marking solar time with sundials and waterclocks set to the sun for thousands of years. This calendar was made obsolete by the introduction of Standard Time. However, the passage of the sun over the Greenwich meridian is still the standard scientific reference of world-time (UTC) for modern timekeeping.
  • Lunar Calendar: In China, India and other eastern cultures people mark time by the cycles of the moon, called lunar time. Because the moon cycles are not exactly a month long, a leap month is added to the calendar now and then so that the lunar calendar changes with the seasons. The Romans saw this as too arbitrary, and so replaced the lunar calendar with the Julian calendar. In Islam, a purely lunar calendar is kept which does not add a leap month and strictly coun as twelve lunar months, and so is about 11 days shorter than the solar year.
  • Zodiac Calendar: Instead of tracking time by the sun or moon, the Zodiac Calendar tracks time by the stars, called sidereal time. Sidereal time is mainly used for astronomical observation. The siderical calendar year, or Zodiac Calendar, has days that are shorter by four minutes. Each year is one day longer because a sidereal day is defined as the time it takes to see the stars in the same position in the sky: 23 hr. and 56 minutes.
How do the positions of the stars change over time? In this experiment you will investigate how the constellations change in the night sky over different periods of time. Will the patterns of constellations and stars in the sky change more in one hour, one day, one month or one year?

Terms and Concepts

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!
  • star
  • constellation
  • time
  • moon
  • sun
  • Which constellations are in your night sky?
  • How do they change over time?
  • Do some stars change more than others?


Here are some helpful websites:

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Materials and Equipment

  • computer
  • Internet
  • printer

Experimental Procedure

  1. First, you will need to decide on a date and time to start your experiment. Choose today's date and write it down along with a time in the evening that you can go outside and look at stars, like 8PM.
  2. Now, get on your computer, connect to the Internet and open up your Web browser.
  3. Type the URL, or Web address, for "The Weather Underground" website into the navigation bar:
  4. At the top, left-hand corner of the page there will be a box where you can type in your city and state. Type in your city and state, or your zip code, and then hit "Enter" or click on "Go."
    Screenshot of the header for the website has a search bar and featured links
  5. Scroll down past the weather information until you see a box with Astronomical data. Click on the "View the Full Star Chart" option at the bottom of that window, beneath the pictures of the moon.
    The website has links to a star chart and astronomy terms under a moon phase chart
  6. You should see a circular picture of constellations and stars. This is the view you can see if you lay down in your backyard tonight, with your head towards the south pole and your feet towards the north pole. You might notice some of the names of constellations because they are also the names of astrological signs like Pisces, Aries, Gemini, or Leo.
    A star chart maps and labels all the constellations
  7. Print out this page using a color printer and write the full date and time on the page. You will see the date and time information to the left of the picture. You can also save the picture to your computer by right-clicking on it and selecting save (for a PC) or by clicking and dragging the picture onto your desktop (for a Mac).
  8. Now, change the time to test one of your variables. To test the one hour variable, change the time one hour ahead of the last star chart by clicking on time and choosing the next hour (change 8PM to 9PM). Print or save the new star chart and write the full date and time on the page.
  9. To test the date variable, change the date to one day ahead by clicking on the date and choosing the next date (change 20th to the 21st). Print or save the new star chart and write the full date and time on the page.
  10. To test the month variable, change the month to one month ahead by clicking on the month and choosing the next one (change May to June). Print or save the new star chart and write the full date and time on the page.
  11. To test the year variable, change the year to one year ahead by clicking on the year and choosing the next one (change 2006 to 2007). Print or save the new star chart and write the full date and time on the page.
  12. Arrange all of your star charts on the table and look for either of the main navigational constellations, Ursa Minor or Crixa. On each page, circle these constellations with a marker.
  13. Try to find your favorite constellation near the center of the chart in the first star chart. Compare that chart to the other charts. Which chart is the most similar? Which chart is the most different? Do the stars change in position more in an hour, a day, a month or a year? Are the same constellations present on each page?

If you like this project, you might enjoy exploring these related careers:

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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. Read more
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Maps can give us much more information than ways to get from A to B. Maps can give us topographic, climate, and even political information. Cartographers and photogrammetrists collect a vast amount of data, such as aerial data and survey data to produce accurate maps and models. For example, by collecting rainfall data, a cartographer can make an accurate model of how rainfall can affect an area's watershed. The maps and models can then be used by policy makers to make informed decisions. Read more


  • Another thing that you can do is view the sky from a particular direction, like North or South. Try looking North for the North Star, called Polaris in the constellation Ursa Minor. Change the month gradually, one month at a time. How do the stars change relative to the North Star? Which direction do they move? Can you use this phenomenon to figure out the direction of the earth's rotation? Why do you think Polaris is a good star for navigating compared to other stars?
  • Try another experiment to compare the night sky during different seasons of the year. Choose a month in the winter, spring, summer and fall. What stars are present in every season? Which stars change throughout the year? How do the stars that you see compare to the Zodiac Calendar? Do the constellations match the calendar?
  • In this experiment we asked how the constellations change in the night sky over different periods of time. Another factor that can change the night sky is your location on the earth. You can change the location of your star chart and compare star charts from different places on the globe. Which other countries have a night sky most similar to yours? Which countries are the most different?

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