### Session 2. The path of the sun

 Total time: 2 hours Objectives: * To determine the path of the sun during the day and its changes during the year* To read a sun chart in order to find the azimuth and altitude of the sun to within 3° Resources: * Bennett, Sun Angles for Design, pp. 27-53* Mazria, Passive Solar Energy Book, pp. 5-13, 302-338* U. S. D.O.D., Magnetic Variation Map of the World* Attachment III-2-A, "Finding Azimuth"* Attachment III-2-B, "Reading a Sun Chart" Materials: Sun angle charts for the latitude of the training site and the latitude of each participant's country (See Trainer Notes, Step 6), sun angle calculator, heliodon, newsprint, felt-tip pens, tape, thumbtacks
 Trainer Notes The sun angle calculator can be purchased from Zomeworks Corporation, Box 712, Albuquerque, New Mexico 87103 (\$60.00). The heliodon plans can be purchased from Farallones Institute Rural Center, 15290 Coleman Valley Road, Occidental, California 95465 (\$3.00).

Procedures:

Step 1. (5 minutes)
Present the objectives and describe the session activities.

Step 2. (20 minutes)
Using the sun angle calculator and the heliodon, demonstrate how to determine the paths of the sun at the training site and distribute the sun angle charts for the latitude of the training site.

 Trainer Notes Once you have set the sun angle calculator to the latitude of the training site, have a participant describe the sun's daily path at several different times of the year. Point out: * The azimuth (compass reading) of sunrise* The altitude (height above the horizon) at noon* The azimuth of sunset for the time of year during training* The equinoxes* The solstices Some sample questions for discussion include: * What are the two days of the year when the sun rises due east and sets due west?* Does this hold true for all latitudes?* How can you calculate the altitude of the sun at noon during the equinoxes?* What does "equinox" mean?* What direction should a solar collector face at the training site?* What would be the tilt of the collector optimal summertime collection, optimal wintertime collection and for year around collection?

Step 3. (20 minutes)
Discuss the path of the sun at the equator.

 Trainer Notes Move the visor of the sun angle calculator to the vertical position (that of the equator) and ask: * What can you say about the day-length on the equator?* What direction would a solar collector face on the equator for optimal collection March through September? September through March? For year-around collection?

Step 4. (10 minutes)
Post the magnetic variation map of the world on the wall and have the participants find the latitude or range of latitudes for the country in which they will be serving.

Step 5. (15 minutes)
Distribute ant discuss the participant's host country sun angle charts and describe how a north latitude sun chart can be converted to a south latitude sun chart.

 Trainer Notes Prior to this session, you should determine the latitude or range of latitudes for each country and prepare one or two copses of the appropriate sun chart (Bennett, pp. 27-53) for each participant. For example, if five participants are going to Zaire (which ranges from 0° to 4° north latitude) and you want each participant to have two copies of each latitude, make 10 copies of 0° and 10 copies of 4° sun charts. * To change a northern latitude sun chart into a southern latitude sun chart, invert the sun paths shown on the chart (June 21 changes with December 21; July 23 and May 20 change with November 22 and January 21, etc.) and invert the horizontal axis, solar azimuth (degrees) so that the numbers read: 180, 160, 140, 120, 100, 80, 60, 40, 20, 01360, 340, 320, etc. * Sun charts for latitudes near the equator can be confusing because it looks as if the sun path goes off the chart to the left. You can clarify this by pointing out that the sun path continues by coming back onto the chart from the right. * Explain that the sun charts are a two-dimensional representation of a hemisphere, so that when the sun path (which travels through the three-dimensional hemisphere) is transferred onto them, some liberties must be taken.

Step 6. (20 minutes)
Distribute and review Attachment III-2-A, "Finding Azimuth," and discuss the magnetic variation at the training site.

 Trainer Notes * This attachment is made for the San Francisco area of California, U. S. A. It is recommended that if this training is done elsewhere, a new Attachment III-2-A be made prior to this session using information found on the Magnetic Variation Map of the World. Attachment III-2-A can be used as a guide. * Explain the reason for a magnetic variation and the difference between an eastern and western variation, using the attachment as a guide.

Step 7. (10 minutes)
Have a volunteer find the magnetic variation 'or the country in which he/she will be serving on the map of the world and indicate it to the group.

Step 8. (10 minutes)
Distribute Attachment III-2B, "Reading a Sun Chart," and have the participants read the instructions and complete it.

 Trainer Notes Allow the participants to work in groups of two or three to complete this attachment. This helps people to learn, reduces competition and strengthens the cooperation of the group.

Step 9. (5 minutes)
Have the group discuss and explain their sun chart computations.

 Trainer Notes * Let the participants determine the answer. Then check to see if it' 5 correct. * Allow participants to make their own corrections. * Explain that it is important to be able to read the sun chart in order to site a solar collector so that it is not shaded during critical hours. * Remind the participants that shade mapping and solar siting will be done in Phase IV: Session 8 and that the sun charts will be needed at that time.

FINDING AZIMUTH

The magnetic variation of the training site is 17°E. This means that Magnetic North is 17° east of True North. It also means that True South is 17° east of Magnetic South (see illustration). The magnetic variation of your host country will be different. It can be found on the Magnetic Variation Map of the World.

The illustration shows the placement of a compass to show the corrected azimuths. By lining up the three points of your eye, the center of the compass and the potential shading obstacle, you can find the azimuth of that obstacle. The angle of the obstacle is found by reading from True North (160° in the illustration).

Key

FINDING AZIMUTH

MN = Magnetic North
MS = Magnetic South
TN = True North
TS = True South