Moon phases

Moon Phases Terms Waxing – moon getting bigger Waning – moon getting smaller Crescent – moon less than half full Gibbous – moon more than half full

What causes phases of the moon? The orbit of the Moon around the Earth. We can only see part of the illuminated portion

What do we see? Half of the Moon is always illuminated Half of the moon always faces Earth Where the halves overlap, we see phases

What do we see? It takes 28 days for the moon to make a complete orbit This means the cycle repeats about once a month

Waxing and Waning Waxing - Moving towards a full moon Waning – Moving towards a new moon

New Moon New moon When the near side is totally in shadow Rises at sunrise Overhead at noon Sets at sunset

Waxing moons Waxing crescent Between new and first quarter Rises after sunrise Overhead in the afternoon Sets after sunset

Waxing moons First quarter Between new and full We see half of the illuminated half Half of half = ¼ Rises at noon Overhead at sunset Sets at midnight

Waxing moons Waxing Gibbous More than quarter but less than full Rises after noon Overhead in evening Sets after midnight

Full Moon When the near side is totally illuminated Rises at sunset Overhead at midnight Sets at sunrise

Waning moons Waning Gibbous Less than full, more than third quarter Rises after sunset Overhead after midnight Sets after sunrise

Waning moons Third quarter Between full and new We see half of the illuminated half Half of half = ¼ Rises at midnight Overhead in early morning Sets at noon

Waning moons Waning Crescent Between third quarter and new Rises at just before sunrise Overhead just before noon Sets just before sunset

Formation of the Moon Where did it come from?

Points to keep in mind Any theory of lunar formation must account for: The moon is as old as Earth, is made of the same rock as Earth Has no water Is getting further away from Earth Has little iron

Did the moon.. Spin off from Earth? Form somewhere else? Form alongside Earth? Form from an impact?

Fission Theory Moon spun off from a rapidly spinning molten Earth Problem – Earth’s gravity should have pulled the bulge back in

Capture Theory Moon formed somewhere else and was captured by Earth’s gravity Problem – something would have to slow down the moon Doesn’t explain lack of water, or moon moving away

Coformation Theory Moon and Earth formed side by side from same accretion disk. Problem – lack of iron, lack of water, moon moving away Earth would have cleared its orbit

Giant Impact theory Mars sized planetoid impacted Earth. Moon formed from debris cloud. Most accepted theory

Giant Impact Theory

How do they stack up Theory Age Composition No water Moving away No iron Fission Capture Coformation Impact