Lesson 5 Notes

Investigating Lunar Phases

I. The Moon reflects the Sun’s light.

a. No matter where the Moon is positioned in its path around the Sun, only half the Moon is illuminated at one time – the half toward the Sun.

b. The exception to the above statement is when there is a lunar eclipse.

c. The Moon rotates on its axis.

i. This means that the side of the Moon that faces the Sun is always changing.

ii. The Moon orbits Earth at the same time that Earth orbits the Sun.

iii. The area of the illuminated Moon that is visible from Earth also changes each day.

apparent shapf the Moon depends on how much of the Moon’s illuminated side is visible from Eart

d. The Moon orbits Earth called phases. Per Encarta

e. The part of Moon that is in its own shadow is called the dark side.

f. When the Moon passes between the Sun and Earth, only the dark side is visible, this called a new moon.

g. When Earth is between the Moon and Sun, the Moon’s entire illuminated side is visible, called a full moon.

II. Moon’s Orbit:

a. The sidereal month (27.3 days) is the time it takes the Moon to orbit Earth one complete revolution.

b. The synodic month is the time it from one new moon to the next new moon, or about 29.5 days.

c. A synodic month is longer than a sidereal month.

i. The Earth has orbited about 1/12^th of the way around the Sun.

ii. The Moon has completed one cycle of lunar phases.

III. Waxing and Waning:

a. The Moon’s cycles is divided into 8 equal parts.

- each part lasts a little over a half a week.

- New moon

- Waxing crescent

- First quarter

- Waxing gibbous

- Full moon

- Waning gibbous

- Third quarter

- Waning crescent

b. During a waxing phase, the illuminated portion of the Moon is continually growing.

c. During a waning phase the illuminated portion of the Moon is continually shrinking.

d. The changes in phase occur because the Moon is orbiting Earth, and we see more or less of its illuminated side each night.