SUN OBSERVATIONS CAUTION: NEVER LOOK DIRECTLY AT THE BRIGHT SUN!

OBJECTIVES The purpose of this lab is to show that the position of the sun in the sky changes according to the time of year and latitude of the observer.

BACKGROUND Much of what we observe of the sun is due to the earth’s rotation and also its tilt on its axis. Because the earth’s axis is tilted 23½o from the vertical,

you cannot always look out from the earth’s equator and see the sun directly overhead. Neither does the sun always rise in the east, set in the west, nor get straight

overhead at “high noon.”

EQUIPMENT You will need a piece of cardboard or plywood and a long nail. You also need a compass and either a protractor or a scientific calculator.

PROCEDURES Observation 1–The sun’s elevation Nail a long nail (3″ to 4″ long) through the center of a board or cardboard (about 1 foot square). Place the board nail-

up on a flat, horizontal sidewalk at noon time (1:00 p.m. if you are in Daylight Savings Time). Measure the length of the shadow that the nail makes at some point

between the hours of 11:00 a.m. and 1:00 p.m. Starting at 11:00 a.m., make a mark at the end of the shadow every 15 minutes. The point where the shadow is the shortest

will be true noon time for your location. At what time did this occur? ______________ What compass direction is the shadow pointing at true noon time? _______________

(If you live in the tropics, you may not have a shadow if the sun is directly overhead.) With a protractor, measure the angle made if you would connect the tip of the

shadow with the tip of the nail. To do this, you can place a ruler on the tip of the nail so that it rests at the end of the shadow. The ruler makes the angle with the

board (see Figure 2 on the next page). This is the angle of the sun’s elevation in the sky.

* \ \ \ \ \ \ nail \ / ==========>\ shadow Figure 2 To make a more precise measurement of the angle, measure the length of the shadow and the length of the protruding

nail. The tangent of the angle is equal to the nail length divided by the shadow length (opposite over adjacent). Calculate this number for the tangent. Punch this

tangent into the scientific calculator and then press [Second] [Tan]. The inverse of the tangent will be calculated, thus giving you the angle. On some calculators,

instead of [Second] you will have an [Alt] button. Example: If the nail is 3″ long and the shadow is 1.5″, then opp/adj is 3 / 1.5 = 2.0. Punching in 2 and then

pushing [Second] [Tan] gives a value of 63.4. So in this case, the sun is 63.4o above the horizon. Observation 2: Sunset or sunrise Take a compass reading of the

center of the sun as it goes down over the horizon. It is diminished in brightness enough to look at it now. Use your reading from the moon lab, if you took one. The

normal apparent size of the sun is the same as that of the moon. When either of them is rising or setting, they appear much larger and richer in color. E. RESULTS AND

CONCLUSIONS Report your calculations and measurements, and answer the following questions. In what part of the sky is the sun when it is at its highest? Would this be

the same for everyone on earth, in both hemispheres? Look up your city’s latitude in an atlas at the library (degrees north or south of the equator). If you live

between 23½o North and 23½o South, the sun does pass straight overhead at sometime during the year. Otherwise, it is always at a lower elevation. / angle “a” ruler

REVIEW AND PRACTICE How fast does the earth actually move? How long does it take for the earth to go around one time? Well, the distance around the equator is about

25,000 miles. Knowing this, at how many miles per hour does the earth go in its daily spin? This is the velocity of the earth’s rotation. The earth also goes around

the sun in 365.25 days. The earth is located 93,000,000 miles from the sun but travels in a slightly elliptical orbit for a distance of 584,400,000 miles (5.844 x 108

mi.). At what speed (miles/hr.) is the earth traveling around the sun (first convert 365.25 days to hours)? Summarize your observations about the sun.

laboratory report should contain the following sections: (1) Hypothesis, (2) Procedures,
(3) Observations and Results, and (4) Conclusions. Make certain you include all four headings with at least a short paragraph for each. In addition, tables, graphs,

and answers to questions may be necessary in the latter two sections.

HYPOTHESIS
Scientific research should contain a preliminary statement of the expected outcome of the experiment. This can include predictions of the specific experiment or the