The Moon’s Motions

After completing this section, students will describe the types of eclipses (Standard PI – 070)

The moon travels in a regular and predictable motion. This explains why we see different

amounts of the moon’s surface

By keeping track of the moon’s motion, we can predict where the moon is in it’s orbit

The Moon’s Orbit

The moon rises in the east and sinks in the west. This motion is

apparent.

This rising motion is caused by the Earth turning on its axis.

The moon is in orbit around the Earth. It takes about 27

and a third days to rotate

The Moon’s orbit is elliptical, with an average distance of 384,000

kilometers

Apogee – when the Earth and the Moon are farthest away from each other

Perigee – when the Earth and the Moon are closest to each other

Phases of the Moon

The phases of the moon are the daily changes in the moon’s

appearance as viewed from the Earth. Moon phases occur because:

• We see the moon because it reflects sunlight

• The Moon orbits around the Earth

The sun lights the half of the moon that is facing us. From the Earth, the

face of the moon changes from all dark (new moon) to all light (full

moon)

This is called waxing.

When the moon goes from all light to all dark, it is called waning

Lunar Eclipses

The shadow cast by any opaque object has two parts.

The umbra is the area of total shadow. The penumbra is the area of partial

shadow

A lunar eclipse occurs when the Earth’s shadow prevents

the sunlight from reaching the Moon

It only occurs at full moon phase.

A total lunar eclipse occurs when the moon is fully within the Earth’s umbra

A partial lunar eclipse occurs when only a portion of the Moon is in the umbra

Solar Eclipse

Solar eclipses occur when the moon comes between the Earth and the Sun

A solar eclipse occurs only at new moon phase

A total solar eclipse occurs when the moon is closest to

the Earth

Areas in the Moon’s umbra experience a total eclipse

Partial eclipse occurs when the Moon is at perigee.

Annular eclipses occur when the moon is at apogee. The

umbra doesn’t reach the Earth