THE MOON'S CHANGE IN APPEARANCE (XX-1)

The problem. Primitive peoples noted the regularity of the moon's changes and measured time by them. The moon receives its light from the sun and reflects a portion of this light to the earth. We recognize the new moon as a thin crescent and the full moon as a brilliant yellow disk. Why do these changes occur? In seeking an answer

blank form suggested on the following page will be useful in keeping the record. It is best to make the observations at least one month before the final class discussion of the subject.

What to do. 1. Refer to a calendar to find when the moon is new. Look for the moon in the evening sky and record the facts suggested in the table on the following page. Estimate the altitude (Fig. 39) in degrees, the distance from either north or south to Z being 90 degrees. A convenient "yardstick" for measuring the sky may be had by considering the distance across the Big Dipper's bowl as 10 degrees.

2. Make as many observations as you can during the month (at the same hour if possible) and record the facts.

3. Assemble the records of the class and compare observations. Make large drawings showing the appearance of the moon at the age of four days, eight days, fourteen days, and twenty days.

Compare these drawings with the photographs found in figures 123 and 124 of the text.

Questions. In what direction from the sun was the moon when first seen? Does the moon rise and set at the same time every night? Where does the full moon appear at sunset? How many days intervene between new moon and full moon? How long will it be before the next full moon? Why does the moon change its appearance from evening to evening?

Suggestions for report. Record the observations in the table.

PLACE DATE TIME

DIRECTION OF
MOON FROM
OBSERVER

ALTITUDE
(DEGREES ABOVE
HORIZON)

DIAGRAM

SHOWING
SHAPE

Prepare a drawing similar to figure 39 showing the path of the moon across the sky, from new moon to full moon. Use the position of the moon at the same hour each evening.

Reference work. Read sections 248 to 255.

Optional problems. Look at the moon with a pair of opera glasses, a pair of field glasses, or a small telescope. Compare your observations with the outline map of the moon in case a well-illustrated textbook on astronomy is available. Devise a demonstration to explain the phases of the moon. Prepare a diagram to show why the moon rises later every night.

THE PLANETS OF THE SOLAR SYSTEM (XX-2)

The problem. Next to the moon the planets are the most readily observed. In all, eight planets, of which the earth is one, revolve about the sun. Like the moon, the planets are observed by means of light reflected from the sun. The seven other planets which revolve about the sun move in the same direction as the earth and in almost the same plane. How many and which planets are visible at this time of the year?

What to use. The Monthly Evening Sky Map * for the current month or a "star and planet chart."

What to do. 1. Find what planets are visible this month. This is best done from the printed information mentioned above, but some almanacs and the first issue of the month of the Scientific American give these facts. Look for the planets in the proper positions in the sky and make one observation and record each evening. Continue observations for two or three weeks if possible.

2. In order to appreciate the relations of the planets to one another and to the sun, a model of the solar system can be arranged to scale as follows: Refer to page 253 of the text and record the names, diameters, and distances of the planets from the sun in a table. Record also the diameter of the sun, the diameter of the moon, and the distance from the earth to the moon. In choosing a scale let one millimeter represent 10,000 miles. Calculate the diameters of the sun, planets, and moon to this metric scale. Likewise calculate the distances of the planets from the sun. Convert this millimeter distance into feet (approximately) by dividing by 305.

3. Place a ball or a circle of the proper size in one corner of the room to represent the sun on this scale. Locate circles of the proper size and distance from the sun to represent the different planets. * May be secured at 150 Nassau Street, New York, 10 cents per copy.

Questions. How can a planet be distinguished from a star?

Does a planet rise and set?
with reference to the stars?
with the eye? Are all of the
new facts do you discover through the use of the model?

Does a planet change its position
Can the planets be distinguished
planets visible to the eye? What

Suggestions for report. Write a story in which you tell what you have done in 2 and 3. Choose some appropriate title relative to the planets and write the story in any form you desire.

PLACE DATE TIME

DIRECTION OF
PLANET FROM
OBSERVER

ALTITUDE

(DEGREES ABOVE
HORIZON)

DIAGRAM CF PLANET AND STARS NEAR IT

Reference work. Read sections 256 to 266.

Optional problems. Observe the planets with an opera glass, a field glass, or a small telescope and write a description of your observations. Where would the following appear in the model worked out in 2 and 3: Sirius (text, p. 273)? Mizar (text, p. 276)? Vega (text, p. 277)? Consult the Evening Sky Map for information on the moons of Jupiter.