Information About Solstices and Equinoxes

Here's What You Need

Here's What You'll Do

Here's What You'll Record

Questions You May Want To Ask

Predictions You May Want To Make

Reference websites

Learning Standards

Shadow Data from 2004 & 2005

Measuring shadows cast by sunlight or moonlight on the Solstices and Equinoxes

This investigation invites you and your students to become astronomers and investigate sun shadows and full moon shadows during the Solstices and Equinoxes.  The longest and shortest days, called Solstices, occur in December and June and the in-between days, called equinoxes, are in March and September. Join people from all over the Earth to measure and record shadows made by a one-meter stick in sunlight and/or the light of a full Moon on these days (or as close as possible depending on weather conditions).  You will use your observations to create models to help explain and understand these yearly changes in the place or position of the Earth, Moon, and Sun.  Doing this investigation gives you opportunities to track and record your own motion as a passenger on planet Earth throughout the year as you better understand the reasons for the seasons.

This investigation can be done by beginning students in grades 1 through 7 and also for advanced students in grades 5 though 12 with minor modifications. 

Materials:  Here's What You Need

All Astronomers:

• A clear sky so we can see the Sun and/or Moon

• A stick or something that is 1 meter or 100 centimeters tall.

• A measuring tape or stick that measures in centimeters.

• An assistant who can help position the stick and take measurements.  The assistant also helps estimate that the stick used to make a shadow is on flat or level ground and that it is straight up and down.

• A watch or clock that is set to the correct time.

• A data sheet or paper and a pen or pencil for recording observations and measurements.

• A flashlight if making observations at night

 Advanced Student Astronomers:

In addition to the materials listed above, you will need the following:

• A carpenter's level that you can use to check that the stick used to make a shadow is on flat or level ground and that it is straight up and down.

Here's What You'll Do

A.   You will measure the length of a shadow cast by a vertical one-meter stick four times during the year.  Observations should be made as close as possible to the March 20 or 21 and September 22 or 23 (the Equinoxes) and June 20 or 21 and December 21 or 22 (the Solstices.    You can find solstice, equinox and Moon phase times and dates from the U.S. Naval Observatory at http://aa.usno.navy.mil/.  On the site, go to "Find it-Index" and look up Solstices, Equinoxes. or Moon, fraction illuminated. 

For Beginners: A good average time for Sun shadow measurement is about 12:30 PM Standard time or 1:30 PM Daylight time.  Full Moon measurements should be at 12:30 AM Standard time or 1:30 AM Daylight time.

For Advanced Astronomers: Use local or true noon or midnight for making observations.  These are the times that the Sun or Moon is exactly North or South of your position and/or halfway between rising and setting.  Go to the U.S. Naval Observatory website at http://aa.usno.navy.mil/data/docs/RS_OneDay.html. and look for the Sun transit and Moon Transit times. You will need to enter the name of the city where you will be making your observations or you can enter your latitude and longitude.  For other ways to calculate local or true noon or midnight, click here.  To find latitude and longitude for your location or a place near you, go to http://www.heavens-above.com/ and click on "Select your location from our huge database." Then select your country and city.

For All Astronomers: 

• Get a one-meter high stick (100 centimeters)

• Predict or guess what you believe the shadow length will be

• Place the stick straight up and down on a flat surface

• With help from a friend, accurately measure the length of the shadow in centimeters.  Measure from the bottom of the object to the end of the shadow.

Now make a list of things you noticed about doing this investigation. Include such things as making measurements, describing the shadow, if the shadow changes, etc.

Here's What You'll Record

Record the following information and e-mail it to: shadowdata@thesciencecenter.org.  Your information will be collected and posted on the website. 

• First name(s) of person(s) making the measurements

• Was this measurement for shadows made by sunlight or moonlight?

• Date of measurement

• Time of measurement

• Length of shadow

• Your latitude and longitude. To find latitude and longitude for your location or a place near you, go to http://www.heavens-above.com/ and click on "Select your location from our huge database." Then select your country and city.

• Location (City/State/Country)

Advanced Astronomers: Should also include the following:

• Length of daylight on the day the observation was made.  There are several ways to find the length of daylight.  Local newspapers, an almanac, or astronomy magazines may have the information or you can access http://encarta.msn.com/media_701500905/Hours_of_Daylight_by_Latitude.html. for information on daylight by latitude. 

• What was the height of the Sun or Moon? Click here to find out more information on calculating the height of the Sun or the moon. 

• What was the direction the shadow was pointing?

Questions You May Want To Ask

You probably have lots of questions and ideas that you want to explore based on your observations:  Here are some other questions that you might want to explore locally using just your data.

• How do Sun shadows change length and direction during the day?

• At what time of day are Sun shadows the shortest?  Longest? 

• At what time of day is the Sun the highest?

•  Where is a full Moon at midnight?

•  How does a full Moon change length and direction during the night? 

•  When can you see the Moon during the day?

• How can we make certain the ground is flat and that the object that we use to make shadows is straight up and down?

• Can you estimate the height of a building or tree by comparing its shadow to the shadow made by the meter stick? 

• What is a good way to make certain that you have a good measurement?

•  When is summer and when is winter on the Earth?

•  What causes the changes in shadows from day to day?

•  Can Sun shadows be used to tell time?

Here are some other questions that you might want to explore lusing data from different places and made at different dates and times: