The Moon: Earth’s ONLY Natural Satellite

Phases and Eclipses

Like the Earth and the other planets, the Moon is illuminated by the Sun.It has a day-side and a night-side of equal size.

North Pole

MOON (from above)

• Of course, the day-side must point toward the Sun, but it doesn’t necessarily point toward the Earth.

• We see different amounts of the illuminated side of the Moon each day, from nothing to a complete circle.

• These are the phases of the Moon (like this crescent).

• This animation compresses one month into seconds.

The Moon’s Phases: Oct. 2007

WANING

WAXING

29.5 days29.5 days

The View from Above

Note: We see different phases at different times of day.

The Evening Sky• At sunset we see

the waxing phases of the moon.

• The farther the moon gets from the sun, the more illuminated it is.

• The light side is on the right, the “sun side.”

The Morning Sky• At sunrise we see

the waning phases of the moon.

• The farther the moon gets from the sun, the more illuminated it is.

• The light side is on the left, the “sun side.”

Another View (We can’t see the green striped sections)

The Predictable Lunar Cycle:

The Lunar Year• The time for one cycle is 29.5 days.• This means there are 12 cycles (or months) in

354 days, which is called a lunar year. • To have a lunar calendar work, you must add

a 13th month every 3-4 years.• Unfortunately, since the moon orbits the

Earth, scientists first thought every thing else did too.

As seen from the Moon, the Earth goes through phases, too.

What moon phase do we see?

There are two important alignments of Earth, Moon, and Sun

SUN

EARTH

1

full

2

new

These are the positions of the eclipses

1. Lunar - Full Moon 2. Solar - New Moon

LUNAR ECLIPSE!LUNAR ECLIPSE!The Full Moon falls into the

Earth’s shadow

The eclipse is total when the moon is in the Earth’s umbra.

Solar Eclipse!The Moon’s Shadow hits the Earth,

covering the Sun.

Types of Solar Eclipses:

• Total Eclipse: Umbra strikes Earth’s surface

• Partial Eclipse: Penumbra strikes Earth’s surface.

• Annular Eclipse: Moon is too far away to completely block out sun. You see a ring.

What We See on Earth…

TOTAL ECLIPSE

PARTIAL ECLIPSE

ANNULAR ECLIPSE

Total Eclipses Show Special Features on the Sun:

The Corona.

Notice the stars in backgroundSolar flares on the sun.

The Chromosphere

Eclipse Views…Eclipse Views…

Why don’t we see eclipses every month?

The full or the new moon must occur at the “X”s for complete alignment of Earth, Moon, and Sun.

Total Eclipse Map

WRAP-UP!• Why does the moon go through phases every

month (approximately)?• When the moon is 180° from the Sun, what

phase is it?• Why do we see the waxing phases in the

evening sky and waning in the morning sky?• Why is a half moon more correctly called the

first or last quarter?• What causes a lunar eclipse?• What causes a solar eclipse?• Why are eclipses relatively rare?