19.3 Phases, Eclipses, and Tides

The moon We only see one side of the moon. The dark side of the moon never faces Earth and has only been seen by astronauts and in pictures. This is because of how the moon moves in space. The moon rotates on its axis every 27.3 days and revolves around the Earth in the same time 27.3 days. Since its rotation and revolution are equal, the same side always faces Earth.

Phases of the moon The changing positions of the Earth, moon and sun cause the phases of the moons, eclipses, and tides to occur. Every revolution around the Earth the moon goes through a set of phases. Because sunlight lights up the moon where the moon sun and Earth are in relation to one another determines whether we see a full, quarter or crescent moon.

Phases of the Moon The phase of the moon you see depends on how much of the sunlit side of the moon faces EARTH.

1. New Moon Dark side faces Earth, lighted side faces Sun Looks like the moon has disappeared This is the first phase in 8 to take place

2. Waxing Crescent Thin slice of the moon is lit up by the Sun and is shown on Earth Occurs about 24 hours after a new moon

3. First Quarter Occurs about a week after a new moon You can see half of the lighted side from Earth Half of the lighted side is also called, one quarter

4. Waxing Gibbous More than one-quarter of the moon is visible from the earth

5. Full Moon The whole surface of the moon facing Earth is lit up Exact opposite of a new moon

6. Waning Gibbous Occurs right after a full moon The amount of the moons lighted side becomes smaller

7. Third Quarter You can only see half of the lighted side from Earth Just like first quarter, but backwards

8. Waning Crescent Occurs just before a new moon The amount of the moon seen on Earth becomes smaller Only a small slice of the moon is shown Cycle begins again at new moon. The entire phases take 27.3 days.

Solar Eclipses

Solar Eclipse Solar Eclipse- occurs when the moon moves directly between the sun and earth and casts a shadow on part of earth.

Parts of a Solar Eclipse Umbra- darkest part of the moon’s shadow. Only a person standing in the umbra can see a total solar eclipse. Penumbra- lighter shadow on the earth’s surface surrounding the umbra. A person standing in the penumbra can see a partial solar eclipse.

Parts (cont.) The only part of the sun that is visible during a solar eclipse is part of its atmosphere, which appears as a pearly white glow around the edge of the eclipsing moon.

Caution!! Regardless where you are, you should never look into a solar eclipse. The light will permanently damage your eyes. Scientists wear special glasses!

Lunar Eclipse Can only occur at Full Moon Moon passes through some portion of Earth’s shadow Penumbra-Earth blocks part of the sun’s rays from the Moon Umbra-Earth blocks all direct sunlight from the Moon

Penumbral Lunar Eclipse The Moon passes through Earth’s penumbral shadow Subtle and quite difficult to observe 35% of eclipses are penumbral

Partial Lunar Eclipse A portion of the Moon passes through Earth’s umbral shadow Easy to see 30% of eclipses are partial

Penumbral Lunar Eclipse The Moon passes through Earth’s penumbral shadow Subtle and quite difficult to observe 35% of eclipses are penumbral

Total Lunar Eclipse The entire Moon passes through Earth‘s umbral shadow Quite striking, vibrant colors 35% of eclipses are total

Total Lunar Eclipse The entire Moon passes through Earth‘s umbral shadow Quite striking, vibrant colors 35% of eclipses are total

Tides Caused by the moon Occur every 6 hours 2 high tides and 2 low tides every day Spring tides: tides are higher than normal Neap tides: are less effective than normal