Lunar Motion & Eclipses

Lunar Phases• Caused by Moon’s changing position around

the Earth

• See dif. portions of the lit half of Moon

• Waxing phases: from new moon to full moon, right side of moon becomes illuminated

• Waning phases: from full to new moon, left side is illuminated & see less of the moon.

Phases of the Moon

Synchronous Rotation• Same side of the Moon faces Earth

always

• Because Moon rotates at the same speed it revolves

General Motion Statistics• Lunar month: time it takes to go

through cycle of phases (29.5 days)

• 27.3 days for moons orbit

• Rises and sets 50 min. later ea. Day

Remember the same side of the moon always faces Earth

?Why?

Lunar Month vs. Orbital Period

General Motion Statistics• Moon’s orbit is tilted ~5o (reason

for infrequent eclipses)

• Perigee: Moon closest to Earth

• Apogee: Moon farthest from Earth

Moon’s Orbit

TidesBulge of ocean water on both sides of Earth

caused by Moon’s gravitational pull

• Spring tide: Moon & Sun cause higher than normal high tides, and lower low (full & new Moon)

• Neap tides: Moon at 90o angle to Sun, difference btwn high and low are not as drastic (Qtr. Phases)

Tides and Phases

Eclipses• Light is blocked from an object, which

causes a shadow on it

• Solar eclipse: Moon’s shadow cast on Earth (can’t see Sun)

• Lunar eclipse: Earth’s shadow cast on the Moon (still see moon, but appears reddish in sky)

Eclipses cont’d• Partial eclipse when observer isn’t

under the concentrated shadow

2 regions of Moon’s shadow• Umbra: Moon’s concentrated shadow

~100mi wide (total eclipse)• Penumbra: Moon’s diffuse shadow

(partial eclipse)

Solar Eclipse

Solar Eclipse

Lunar Eclipse