The Moon and Moon Phases

Moon Orbits the Earth – but appears to rise in the east and set in the west due to earth’s faster rotation 13 ° a day rotation of moon compared to 15° per hour of earth --- earth rotates faster than the moon revolves around the earth

Moon’s Rotation = Moon Revolution rotation period = 27.3 days revolution period = 27.3 days Moon shows the same “face” to the Earth Velocity: 360°/27.3 days = 13° per day

Daily Movement of the Moon Each day the Moon rises in the east and sets in the west as a result of the Earth's rotation. It moves about 13° eastwards against the background of stars as a consequence of its revolution around the Earth.

Moon Phases Half of the moon is always receiving light from the sun. The “lit” portion that is visible to earth varies as the moon REVOLVES around earth. THIS CAUSES THE PHASES OF THE MOON. Visible portion of moon growing = waxing Visible portion of moon shrinking = waning

Lunar Phases

How much of the moon we see depends on where the moon is in its orbit: Appearance:

Appearance:

Appearance:

What we observe from earth

Cycle of Lunar Phases Takes 29.53 days This is because when moon gets back to its original position in 27.3 days, the earth has moved 1°/day or about 27°. The moon moving at l3°/day takes about 2 days to catch up with Earth and align with it and the sun in a new moon phase. The moon rises above the horizon at a different time each day (or night). This happens because every time Earth spins around once, the moon moves about l3° eastward along its orbit. The earth must rotate an extra l3 deg. More each day for a point on its surface to be roughly under the moon again. Earth takes 50 minutes to spin 13 deg., the moon rises about 50 minutes later each day and sets about 50 minutes later as well.

Lunar and Solar Eclipses The Moon orbits the Earth, and travels with the Earth about the Sun.  Sometimes the Moon gets between the Earth and the Sun, causing solar eclipses, and sometimes the Moon goes into the Earth's shadow, causing lunar eclipses.

Solar Eclipses – can occur only during the new moon phase Lunar eclipses – can occur only during the full moon phase

The Cause of Eclipses: Shadows

Lunar Eclipses

Solar Eclipses

If Lunar eclipses happen in the full moon phase and solar eclipses happen in the new moon phase, why don’t they happen every month??? As the Moon orbits the Earth, its orbit is tilted slightly (about 5 degrees) from earth’s orbital plane (ecliptic) The moon crosses earth’s plane twice during its orbit.  If this crossing happens at the new moon phase, the Moon will be lined up with the Sun and pass in front of it. This alignment has to be perfect in order for the Moon to completely cover the Sun for a total solar eclipse (the sky will darken just like nighttime, and the stars will be visible) Total solar eclipses last about 7 minutes and occur in a very narrow range across Earth. Full moon phase = total lunar eclipse if perfect.

Solar Eclipses Occur when moon’s orbit intersects ecliptic during the new moon phase

Total Solar Eclipses only last about 7 minutes in a very narrow range across Earth

Daily Cycle of Tides Driven by the gravitational pull of the moon and Sun Affected by nearness of the moon more than the size of the Sun As earth rotates, the tides move around the Earth alternating between high and low tides approximately every 6 hours.

Spring Tides – Neap Tides Tidal range: Difference in height between high tide and low tide Spring Tides: new and full moon phase – greatest range Neap Tides: 1st and 3rd Quarter phases – smallest

Moon motion like all celestial bodies except planets which sometime appear to undergo Retrograde Motion

Retrograde Motion