Figure Eight in the Sky: Making an Analemma
Objective: To see how the sun, as a “clock,” does not always agree with your watch.
Activity
1. Read the Background information provided.
2. Use table 26-1 and coordinate system graph provided to create an analemma.
Procedure: Choose a date, say February 14. Refer to table 26-1 to find the sun’s declination for that date, and how far
behind or ahead of your watch it is. For February 14, the sun’s declination is -13° and it is 14 minutes behind your watch.
Next, on the graph, find -14 on the time line and -13° on the declination line. Lightly draw a straight line through both
points until they intersect. Make a dot at their intersection and mark the date “2/14”; then erase the lines you drew. Do this
for at least thirty-five dates and then connect the dots. Congratulations! You have made an analemma.
Note: The dates on your analemma graph are a mirror image of the actual data collected for this activity because the
shadow analemma is a reversal of the analemma in the sky (see Fig. 26-4).
Analysis and Conclusions Questions
1. What is an analemma? What is its purpose?
2. What is the angle between the ecliptic and the celestial equator? What is the significance of this number?
3. What two pieces of daily information is provided by the analemma?
4. The north-south span of the analemma figure covers _____________ degrees. How is this measure derived?
5. In which direction does the sun move in relation to the ecliptic?
6. During what time of the year does the sun move the slowest? The fastest? How do the differing speeds relate to
the distance from the earth to the sun?
7. Why is the motion patterns described to in #6 referred to as the “True Sun”?
8. What is the “Average or Mean Sun”?
9. What do the “Sun Ahead” and “Sun Behind” sections of the analemma (see fig. 26-3 of your handout) refer to?
10. On the analemma, how is “noon” determined?
11. The sun reaches “noon” when your watch reads 12:00 noon only four days of the year (in other words, 12:00 noon
True Sun and 12:00 noon Average Sun overlap exactly on only four days of the year). What are these four days?
12. Regarding question #11, if your watch reads 12:00 noon and the sun is behind clock time, it will appear slightly
______________ of the meridian (imaginary line in the sky that runs due north to south). When ahead of clock
time, the noon sun appears ________________ of the meridian.
13. During what months of the year is the sun running behind? Ahead?
14. The vertical span of the analemma is a direct result of what?
15. During what time of the year is the sun highest in the sky (closest to the meridian and at the top of the
analemma)? The lowest (furthest away from the meridian and at the bottom of the analemma)?
16. What 2 things determine the horizontal span of the analemma?
17. How does the Earth’s elliptical orbit affect the horizontal span of the analemma?
DO NOT GUESS.
USE A RULER!
horizontal Axis - time (minutes)
vertical Axis - declination (degrees)