Why does the moon appear to change shape over a month?

Phase: different shape of the moon as seen from Earth

Phases are caused by the changing relative position of the moon, Earth, and sun.

Phases are not caused by the Earth’s shadow falling on the moon

The phases occur every month because the moon orbits Earth in 29.5 days

Half the moon is always in sunlight. But, the moon moves! From Earth we see the moon at different angles and the phase is determined by how much of the sunlit side we see.

Let’s take a look… Moon Phase Simulation

Practice Moon Phases at Home

Moonlight Review Curtis: The Moon reflects the light from the Earth. Chet: The light from the Sun bounces off the Moon. Clarence: The Moon gets its light from distant stars. Fallon: The Moon absorbs light from the Sun during the day. Deirdre: There is light inside of the Moon that makes it shine

TIDES

Tide: the periodic rise and fall of the level of water in the ocean

“Tides are one of the most reliable phenomena in the world. As the sun rises in the east and the stars come out at night, we are confident that the ocean waters will regularly rise and fall along our shores.” Why?

Remember the force of gravity depends on distance between two objects and their masses

Tides are caused by how gravity from the moon and sun pull on different parts of Earth

Spring Tide: gravity of sun and moon pull in the same direction = extra high tides and very very low tides Spring from “springen” the Old English word meaning “to jump”

Neap Tide: sun’s pull is at a right angle to the moon’s pull = moderate tides

Rise and fall of oceans occurs every 12.5 hours = 2 high tides and 2 low tides each day

How does this work? In England biscuit = cookie

...but it does create eclipses The Earth’s shadow does not create moon phases…

Eclipse: the partial or total blocking of one object in space by another When an object in space comes between the sun and another object its shadow causes an eclipse

Umbra: darkest part of shadow Penumbra: part of the shadow surrounding the darkest part

When viewed from Earth: People in the penumbra see a partial eclipse People in the umbra see a total eclipse

Solar Eclipse: The Moon passes between the Earth and the sun, casting a shadow on Earth The moon blocks sunlight from hitting Earth

Wait, the sun and moon aren’t the same size! Why do the appear the same size during a solar eclipse?

The sun’s diameter (distance across) is 400 times greater than the moon’s diameter. But, the moon is 400 times closer. Result: Appear the same size and the moon can cover the sun during a solar eclipse

Lunar Eclipse: Earth’s shadow falls on the moon Earth is directly between the full moon and the sun

Why does the moon look red during a lunar eclipse?

The moon orbits Earth about once a month so… Why don’t eclipses happen every month?

Eclipses don’t happen every month because the moon’s orbit is tilted compared to the sun’s orbit This means the moon usually passes above or below the sun

Lunar eclipses are more common but less frequent than solar eclipses ?

That means: Solar eclipses happen more often. But when a Solar eclipse happens only a small number of people can see it. When a Lunar eclipse happens that whole half of the world can see it. So YOU will have more opportunities to see lunar eclipses than solar eclipses.