ESES Unit 2

LUNA, OUR MOON

WARM UP

• Write 3 things you know about the Moon.

SOLAR ECLIPSES

• We happen to be alive at a time when the Moon and the Sun are about the same size in the sky.

• This means total solar eclipses are possible – the Moon can completely block out the Sun.

SOLAR ECLIPSES

• Question: If the Moon revolves around the Earth then why isn’t there a solar eclipse each month?

• Answer: The plane of the Moon’s orbit is not flat relative to Earth’s orbit around the Sun. So some months there are partial eclipses, and most months no eclipse at all.

LUNAR ECLIPSES

• Since the Earth is much larger than the Moon, it casts a larger shadow, and any time the Moon passes through Earth’s shadow we experience a lunar eclipse.

PHASES

• Waxing moon – visible segment growing each day

• Waning moon – visible segment shrinking each day

• New moon – all dark

• Crescent moon – a quarter-full

• Half-moon – self explained

• Gibbous moon – three-quarters full

• Full moon – a lovely circle

PHASES

CONSERVATION OF ANGULAR MOMENTUM

• The Moon is getting further and further away.

• The Moon’s gravity pulls on the oceans and causes the tides, that creates drag friction on the spinning Earth, causing our rotation to slow slightly.

• Our day gets slightly longer every year.

• If the Earth’s rotation slows down, then the Earth loses angular momentum to the Moon.

CONSERVATION OF ANGULAR MOMENTUM

• Angular momentum can’t be created or destroyed – it is conserved.

• So if Earth loses angular momentum then the Moon gains angular momentum.

• Moon revolves around the Earth a little faster, and moves into a slightly wider orbit.

• The Moon is receding at 38 mm per year.

• Eventually it will move far enough away that total solar eclipses no longer happen.

CONSERVATION OF ANGULAR MOMENTUM

• Students having fun! Not in this class, obviously.

TIDAL LOCKING

• Tidal locking results in the Moon rotating about its axis in about the same time it takes to orbit Earth.

• The Moon always shows the same face to the Earth.

TIDAL LOCKING