Phases, Eclipses, & Tides
Section 1-2
Motions of the Moon
✴ The moon revolves around
Earth and rotates on its axis.
✴ It takes the moon the same
amount of time (27.3 days) to
make one revolution and one
rotation.
✴This is why we always see the
same side of the moon.
Phases of the Moon
✴ The moon does not produce its
own light. Instead, it reflects
light from the sun.
✴ The different shapes of the
moon you see from Earth are
called phases.
✴ The moon goes through a
whole set of phases each time it
orbits Earth.
What Causes Phases?
✴ Half of the moon is always lit by
the sun, but the side that faces
Earth is not always the half that
is lit.
✴ The phase you see depends on
how much of the sunlit side of
the moon faces Earth.
✴ This changes based on the
positions of the moon, Earth,
and sun.
The Cycle of Phases
✴ The moon’s phases progress
from new moon, to full moon,
then back to new moon.
✴ The new moon is when the side
of the moon facing Earth is
completely unlit.
✴ The full moon is when the side
of the moon facing Earth is
completely lit.
Eclipses
✴ When the moon’s shadow hits
Earth or Earth’s shadow hits the
moon, an eclipse occurs.
✴ There are two types of eclipse:
solar and lunar.
✴ The moon does not cause an
eclipse most months because
its orbit is tilted compared to
Earth’s orbit.
Solar Eclipse
✴ A solar eclipse occurs when the
moon passes between Earth
and the sun, blocking sunlight
from reaching Earth.
✴ Two different shadows are cast
during an eclipse:
✴umbra: smaller, darker shadow
✴penumbra: larger, fainter shadow
Total Solar Eclipse
✴ If you stand within the area of
the moon’s umbra, you will see
a total solar eclipse.
✴ In a total solar eclipse, the
sun’s light is completely blocked
by the moon.
✴ It is much rarer to see a total
eclipse than a partial eclipse.
Partial Solar Eclipse
✴ If you stand within the area of
the moon’s penumbra, you will
see a partial solar eclipse.
✴ In a partial solar eclipse, part of
the sun is still visible.
✴ It is much more likely to see a
partial solar eclipse than a total
one.
Lunar Eclipses
✴ A lunar eclipse occurs at a full
moon when the Earth is directly
between the moon and the sun.
✴ During a lunar eclipse, the
moon is in Earth’s shadow, and
so it appears dark.
Total Lunar Eclipse
✴ When the moon is in Earth’s
umbra, you see a total lunar
eclipse.
✴ Unlike a solar eclipse, a lunar
eclipse can be seen from
anywhere on Earth the moon is
visible.
Partial Lunar Eclipse
✴ A partial lunar eclipse occurs
when Earth, the moon, and the
sun are not quite in line.
✴ It happens when the moon
passes only partly into the
umbra of Earth’s shadow.