What is a Shadow Stick?
The shadow stick is any vertical, straight, object that casts a shadow. Shadow sticks can be telephone poles, a flagpole, or even a person standing. The shadow cast from a shadow stick may be used to observe the apparent motions of the Sun throughout the day much in the same manner that the shadow cast by the gnomon on a Sundial is used to tell time. However a shadow stick is not as accurate as a sundial for determining time.
In the morning a shadow stick casts a long shadow toward the western horizon. At mid-day the Sun is highest in the sky over the horizon. In the northern hemisphere the Sun will be due south, while in the southern hemisphere the Sun will be due north. The shadow is at its shortest length, and points directly toward geographic north in the northern hemisphere and directly toward geographic south in the southern hemisphere. During the afternoon or evening, as the Sun starts to set, the shadow stick once again casts a long shadow, but this time toward the eastern horizon.
How do you suppose this would be different from the equator?
As the tilted Earth revolves around the Sun, we notice that the Sun's mid-day height varies each day. During the summer it is higher, and during the winter it is lower. The Sun's height above the horizon is called altitude, and is measured in degrees up from the horizon. Measuring the mid-day altitude about every two weeks throughout the year will show the range of the Sun's apparent movement with respect to the observer's latitude location as well as the Sun's movement relative to the Earth's equator. This apparent movement north or south from the equator is a result of the Earth's axial tilt of 23.5o, which in turn is amount the Sun moves north or south of the equator.
Measuring the Sun's height above the horizon may easily be conducted with a student using a pencil as the shadow stick, or having the student actually serve as the shadow stick. The method for determining the Sun's altitude is a process in which a triangle representing the shadow stick and its shadow is made (as shown in the image), or drawn on paper so that the angle the Sun is above the horizon may be measured.
The local time of mid-day may be determined by looking at a newspaper for the times of sunrise and sunset. Use these two times to determine the length of the day in hours and minutes. Then divide the day length by two and then add that amount to the time of sunrise to see when mid-day will occur.
The mid-day altitude of the Sun may be generated using an online ephemeris, such as the NASA Ephemeris Generator .
You may download additional directions for measuring the Sun's altitude, and the Data Sheets from the Links page.