Phases of the Moon Exercise

Phases of the Moon Exercise Name date

In this exercise, you will investigate the cause of the phases of the Moon. The figure below shows an orbital diagram of the Earth-Moon system as viewed from above the Earth's north pole. Light from the Sun is coming from the left. Note that the drawing is not to scale.

Section I

Shade in the part of the Moon that is in shadow and the part that is unobservable from Earth in each of the eight numbered positions. The first has been completed as an example. (Use dark shading for the shadow, light cross-hatch for the unobservable side.)

Section II

Record the phase and appearance of the Moon in Table 1 for each of the eight positions in the diagram. (Again, the first has been done as an example.) Also determine the Moon's elongation. Note that if you know the Moon's elongation, you know its phase, and vice versa. Position 1 Position 2 Position 3 Position 4

waxing crescent 45°

Position 5 Position 6 Position 7 Position 8

The celestial sphere turns once every 24 hours. During this time, a point of the sky has traveled through the angle of 360° or one complete circle. The angle of 360° is equal to 24 hours. (360° ÷ 24 hours = 15°/hour). The Earth will then rotate 15° in one hour. The angle 90° is one quarter of a complete circle. (360° ÷ 4 = 90°) One quarter of 24 hours is 6 hours. The angle 90° expressed in time units is 6 hours. Therefore, the elongation angle is 90° and the phase of the Moon is the first quarter. The Moon will lag 6 hours behind the Sun in rising. When the elongation angle is 270°, the Moon phase will be the third quarter and the Sun lags behind the Moon by 6 hours.

Section III: Use the diagram to fill in the missing data.

Phase of Moon Time of Day Moon's Position in Sky

00:00 (midnight) rising in the East waning crescent 15° above Western horizon waxing gibbous 20:00

12:00 (noon) directly overhead