Lesson CCXXXII

The Relation of the Sun to the Earth.

Leading thought—The sun which is the source of all our light and heat and, therefore, of all life on our globe travels a path that is higher across the sky in June than the path which it follows in December, and hence we experience changes of seasons. The lesson should be given to the pupils of the upper grades and should be correlated with reading, arithmetic and thinking.

Observations—1. What does the sun do for us?

2. At what time of the day after the sun rises do we get the least heat from it? What hour of the day do we get the most heat from it?

3. Is the sun equally hot all day? Why does it seem hotter to us at one time of the day than at another?

4. At what hour does the sun rise and set on the first of the following months; February, March, April, May and June?

5. Which is the shortest day of the year, and how long is it?

6. Which is the longest day of the year, and how many hours and minutes are there in it?

7. What day of the year is the sun nearest a point directly over our heads at mid-day?

8. Which day of the year is the sun at mid-day farthest from the point directly above our heads? Explain why this is so.

9. Standing in a certain place, mark by some building, tree or other object just where the sun rises in the east and sets in the west on the first of February. Observe the rising and setting of the sun from the same place on the first day of March and again on the first of April. Does it rise and set in the same place always or does it move northward or southward?

10. Is the sun farthest south on the shortest day of the year? If so, is it farthest north on the longest day of the year?

11. At what time of the year does the sun rise due east and set due west?

12. The sun is so much larger than the earth that its force of gravity is twenty-seven and two-thirds times that of the earth. How much would your watch weigh if you were living on the sun? How much would you yourself weigh if you were there?

13. Experiment. A shadow stick—Place a peg two or three inches high upright in a board and place the board lengthwise on the sill of a south window or where it will get the south light. Note the length cast by the shadow of the peg during a sunny day and draw a line with pencil or chalk outlining the tip of the shadow of the stick from 9 a. m. to 4 p. m. Make a similar outline a month later and again a month later and note whether the shadow traces the same line during each of these days of observation. Note especially the length of the shadow at noon.

Another excellent observation lesson for teaching the fact that the sun travels farther south in the winter, is to measure the shadow of a tree on the school grounds at noonday once a month during the school year. The length of the tree shadow can be measured from the base of the tree trunk, a memorandum being made of it.

14. When does the stick or tree cast its longest shadow at noon—in December or February? February or April? April or June? Why?

Topics for English themes—The size and distance of the sun. The heat of the sun and its effect upon the earth. What we know about the sun spots. Our path around the sun.

Supplementary reading—Starland, Ball; The Earth and Sky, Holden.