What better reason to do something different in your classroom this month than the celebration of the spring equinox?

March 20 is the official start of the spring season because the hours of day and night have approximately the same length on this day. It is also known as the vernal equinox, from the Latin for “equal night.” On this day, when the sun is at a right angle to the Earth’s axis, both the northern and southern hemispheres get the same exposure to the sun. It is a great day to focus on the sun and engage your students in some activities to learn more about it.

Effects of Sun Exposure

Divide the students into groups to perform tests of the accuracy of the SPF (Sun Protection Factor) rating of sunscreen lotions and sprays. Provide the students with at least three different commercial brands of sunscreens with different SPF ratings. Testing can be done on ultraviolet beads which are inexpensive and come in assorted colors. Students must devise their own methods to test the various sunscreens on the UV beads to determine if they are accurately labeled for sun protection. The results of the students’ testing can be compared among the groups. The activity can also be expanded to include testing on sunglasses by checking at least five of the commercial brands for their effectiveness against ultraviolet sun rays. Supplementary materials are available on the Stanford Solar Center website. Encourage students to learn more about the effects of UV rays and the risk of skin cancer.

Spring Equinox

Photo Credit: Flickr Creative Commons

Is the Sun Yellow?

Use this spring equinox to help students discover that the sun is not really yellow, but white. Start this activity with some simple tests by having your students observe sunlight reflecting off the walls of a white building or a piece of white paper. Have them observe sunlight through a pin-hole camera. Show the students pictures of the sun taken from space where it does appear white. Helping your students understand that the sun is actually made up of many colors in the spectrum, which appear to the human eye as white, can then be taken a step further by allowing your students to experiment by making and spinning a color wheel. This activity also provides a great opportunity for you to collaborate with the art department!

Experiment with Water and Light

Students can conduct a hands-on experiment by filling a box-shaped clear plastic or glass container with water. Using a strong flashlight, shine this white light through the water in the container. They will see that the image exiting the water is white, demonstrating that the wavelengths making up white light pass straight through the atmosphere with no color distinction. Then have the students add a small amount of milk or powdered cream to the water. This milky quality will represent the Earth’s atmosphere. They will observe that the white light passing through the molecules in the Earth’s atmosphere are yellow or orange – the colors we observe in a sunset or sunrise. More of the shorter-wavelength colors are removed when the sunlight must cover a longer distance than when directly overhead, and the reds, oranges, and yellows are left. For more information, check out this Drive-by Science activity guide from the Stanford University Solar Center and NASA.

Global Dimming Versus Global Warming

Most of your students have probably heard of global warming, but there is a little-known climate phenomenon called global dimming, or a drop in measured sunlight. Have students try this experiment in water evaporation on the spring equinox to allow students to determine energy changes as evaporation is largely influenced by sunlight. An outdoor location which is level and isolated should be identified and two identical pans of water should be placed, one in an unsheltered location, and one in a shaded location, close to each other. Each pan should be measured at about the same time morning and afternoon. After each measurement, the pan should be refilled to the exact level of the starting point. A rain gauge must be placed near the pans so that any rain water added can be taken into consideration. An analysis of the data collected can be evaluated. Students can average the other variables of air temperature, relative humidity, and wind speed in determining their results. Charts and more information are available at here.

Studying the sun will bring a change from the students’ indoor studies and draw their attention outside and to the sun’s warmth and light. Learning is always more fun when you experiment, so this spring equinox, take your students into the sun’s glow and bask in the light!

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