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02   Where Is the Sun?

About this Activity
During the course of the year, we all notice that the Sun appears at different places during the same time of the day. At 6 P.M. in July it's still sunny outside, while at 6 P.M. in January the Sun has already set. It's easy to notice difference over the course of months, but what about the difference over weeks or even days?

solar images
This snapshot of the Sun was taken by the Transition Region and Coronal Explorer (TRACE) Observatory.

With this activity you can verify that the Sun appears in a different location at a specific time every day of the year with one exception. On March 21, the Vernal (spring) Equinox, and September 21, the Autumnal (fall) Equinox, you will find the Sun in exactly the same position in the sky.


 What You'll Need
1 - 2 x 2-foot (60 x 60 centimeter) wooden board or cardboard square

1 - 10 to 12-inch (25 to 30 centimeter) wooden stick, 1/4 to 1/2 inches (6 to 12 millimeters) in diameter

1 - tube of glue

1 - marker




















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What to Do

Glue the wooden stick to the cardboard square so that it stands upright (as shown in the sketch below). To assure that the full shadow fits on the cardboard, you may want to glue the stick closer to one of the edges.



Once the glue is dried and the stick can stand by itself, place the cardboard square on a flat surface where it will be exposed to the Sun. Take note of the time of day. Mark the point on the board where the tip of shadow is located and write the date.


3 It is very important that the board be oriented in the same direction each time you lay it on the ground to mark the board. You might mark one of the edges of the cardboard square as a point of orientation.
4 Repeat this daily or weekly at the exact same time each day.
5 Discuss your observations with your family. Ask them if they think that there are any days where the shadow will appear in the same place at the same exact time. Ask them if they think that there are places on the planet where the shadow would appear at the same place at the same time every day.


What's Going On
The cause of the change in the shadow's location (i.e. the location of the Sun) is the tilt of the Earth's axis which causes the Earth to face the Sun at an angle of 23 degrees. Depending on where the Earth is located in its orbit around the Sun determines the length of the day. Since the Earth's location around the Sun is changing continuously, so are the length of the days.

The only two days where the Sun's location matches at any time are March 21 (Vernal Equinox) and September 21 (Autumnal Equinox).

The only place on the Earth where the Sun's location matches everyday is on the equator.

If your family continued this experiment the whole year round and connected the dots of your markings, the picture would look as follows. (Note the point of intersection. That point is where March 21 and September 21 fall.)

Related Websites

"equinoxes, precession of the" From Britannica Online

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