Background:
Many cultures traced the apparent path of the sun through the sky in the course of the year. They traced the path by marking the shadow cast by a stationary object at the same time every day. This path is called an analemma.
To trace the apparent path of the sun takes an entire year. Many cultures used the analemma to make annual predictions about seasons and daylight hours, and to plan important community festivals.
There are four days in the solar pattern that were very important in ancient observations. On the spring and autumn equinoxes, the sun appears to be directly over the equator and the hours of day and night are equal. Equinox comes from the Latin words aequi = equal, and nox = night.
During the summer solstice (June 21), the sun rises very early and sets very late. The reverse is true during the winter solstice (December 21). The sun appears to "stand still" as it reaches its highest, midday point above the horizon in summer, and then its lowest midday point in winter. Solstice comes from the Latin words sol = sun and stare = to stand.
Concept:
The seasonal variations in the path of the sun through the sky are a consequence of the revolution of the earth around the sun. If we start at a given place on the earth, we see the daily path of the sun vary through the seasons. The variation is greater at higher latitudes and smaller at lower latitudes.
Objectives:
- Students will use an analemma ("appears" in the Pacific Ocean on some older globes) to observe the regularity of the sun's pattern over a year's time.
- Students will find the equinox and solstice dates, and be able to determine relative daylight hours based on latitude and date.
- Students will identify the apparent path of the sun during the four seasons.
- Optional: As a long term project, students can trace their own analemma.
Key Vocabulary
solstice, equinox, analemma, equator, latitude
Materials:
- Analemma
- Cardboard same size as analemma
- Glue
- Colored stick pins
- Globes
- Almanac
(For optional activity, a stationary pole or post on school ground, some kind of permanent marking device, i.e., paint, wooden pegs.)
Pre-Assessment:
Ask students to draw a picture of what they think the sun's path would be in the sky during a year.
Procedure:
- Introduce the students to the analemma. What shape does the sun's path make? Is this what you predicted? Identify the degrees latitude and find the equator. Identify the directions north and south. Have students find the names of the months and the numbers that identify the dates. Practice using the analemma by asking students to find the latitude connected with certain days. (For example, March 30 is at 3°ree; latitude; November 10 is at 17°ree; latitude, etc. Use a transparency of the analemma and an overhead projector to help with the demonstration.)
- Review with students that this is the apparent path of the sun. The earth is moving around the sun in an orbit. The tilt of the earth's rotational axis as it orbits and the daily rotation of the earth around its axis is what makes the sun appear to be moving throughout the year. (See Step 7 in the Procedure for "What Makes the Seasons?" for an activity to review this concept if necessary.)
- Have students glue their analemma to the cardboard and put a pin in today's date and their birthday. Ask them if their birthday will have more or less daylight hours than today. Use a globe to find your latitude and relate it to the analemma.
- Using the definition for equinox, have students find the date for the spring and autumnal equinox for the Northern Hemisphere and for the Southern Hemisphere. Mark the dates with pins. (Note: In the Northern Hemisphere, the spring equinox is March 21 and the autumnal equinox is September 23. The sun is directly over the equator, 0 degrees latitude. In the Southern Hemisphere, March 21 is the autumnal equinox and September 23 is the spring equinox.)
- Have the students find the winter solstice, the date the sunlight hours are fewest for the Northern Hemisphere, and the solstice for the Southern Hemisphere. Mark those dates with different colored pins. (NOTE: The winter solstice is when the sun's midday point is the lowest above the horizon. For the Northern Hemisphere it is Dec. 21, and for the Southern Hemisphere it is June 21.)
- Have students identify those months when the amount of daylight would be the greatest and the least, and those months when the amount of daylight is getting longer and getting shorter. What seasons correspond to these months? Color that section of the analemma red that corresponds with summer, blue for winter, green for spring, and yellow for fall.
Optional: Building a School Analemma
- Find a stationary pole or post on the schoolgrounds. Figure out some way of permanently marking the pole's shadow. If your surface is black top or concrete use some kind of permanent paint. If your surface is soil use wooden pegs that you can pound into the soil as markers. Choose a day of the week and a time of day that your students can mark the tip of the pole's shadow. Make sure it's the same time of day every week. If it's raining or overcast, mark the shadow's tip at the next possible day. This is a long term project. It will take a year to make a complete analemma. However, after several months, the curve of the analemma should become apparent. Compare your direct observation with the paper copy of the analemma.
Conclusion:
On what day does the sun's location give us the fewest number of daylight hours? The most? What are these days called? How did you determine when the equinox is? Why is the date of the spring equinox in the Northern Hemisphere the same as the autumnal equinox in the Southern Hemisphere? How many hours of sunlight will we have on today's date? Use the analemma to predict if we will have more or less sunlight tomorrow, one day next week, next month. If you lived in the Southern Hemisphere would you have colored your analemma the same way for the seasons? Why or why not?
Assessment:
- Using your observations and reading of the analemma, describe how this "sun map" could help a community plan its yearly activities.
- Find specific dates on the analemma, predict the amount of daylight hours. Check your prediction with an almanac. Illustrate the position of the earth in relationship to the sun on those dates. (How is the earth tilted?)
Extentions:
Social Studies:
Have students research ancient buildings and temples that were constructed to take into account the east-west lines of the sun, and the equinox and the solstice. What significance did these solar occurrences have to these cultures? What holidays were celebrated then? What holidays do we celebrate around these times of the year now? Compare and contrast. Some examples are The Great Pyramid of Egypt, Chinese temples, Cathedrals in the Middle Ages, Amon-Ra in Karnak, Egypt, Stonehenge, Native American medicine wheels, Mayan temples.
Geography:
Use maps and globes to have students practice using latitude and longitude to identify position.
Art:
Have students make an Aztec calendar (see resource list for references). Have students design symbols to represent the four seasons. Have them arrange the symbols in a pattern to show the seasonal cycle.
Home Extension:
Ask students to trace an analemma at home with their parents. Place a large piece of paper on the wall opposite a sunny window. Put something on the window (a piece of tape) that can cast a shadow onto the paper. Mark the shadow cast on the paper at the same time of day every week. They should begin to see the analemma's pattern appear. Have students explain to their parents what's happening.
4-7 Lesson 2: