The Moon

Origin Step 1: A Mars-sized object hit Earth ~4.5 billion years ago. It hit so hard that debris was shot out into space around Earth Step 2: The debris settled into orbit and its gravity started to pull it together to form the moon

Step 3: Meteorites kept hitting the surface, melting it to make a ‘magma ocean’. Low-density material floated to the top, while high-density material sunk into the core. Step 4: The outer crust cooled and solidified forming light-colored lunar highlands. Meteoroids hit, forming impact craters. Some hit so hard that magma erupted from beneath the crust to fill the craters. This solidified lava is what makes the black maria (or ‘seas’) on the Moon’s surface Step 5: For the past 3 billion years, the moon has been almost completely solid. Only small meteoroids still hit, forming tiny craters.

Lunar Characteristics Lower gravity – because it is smaller & less dense, you would weigh 1/6th of your Earth-weight No magnetic field – because it has no spinning liquid core, compasses won’t work No atmosphere – no weather or wind, so footprints remain for centuries

The Moon’s Orbit The moon orbits the Earth in an elliptical orbit that is tilted about 5° from Earth’s orbit and that has a period of 27 1/3 days. The moon rises & sets 50 minutes later each day Rotation = Revolution, so same side is always facing Earth Apogee – when moon is furthest away from E Perigee – when moon is closest to E

Moon Phases Half of the moon is always receiving light from the sun at any time (except during a lunar eclipse) Phases- the varying amounts of the lighted moon seen from Earth The phases of the moon are cyclic. The period from one full moon to the next is 29 ½ days = one lunar cycle Caused by the changing relative positions of the moon, the sun & Earth From Earth, we only see 59% of the moon’s surface

Moon’s Phases through the Lunar Month Moon Phases Moon’s Phases through the Lunar Month

Moon Phases Inner circle shows view from above. Outer circle shows view from Earth.

“New” Moon When the moon is between us & the sun, we only see the ‘dark’ side of the moon (it’s all dark – we usually don’t see anything!)

“Waxing” Moon When the part of the moon we see lit by the sun is increasing 1st Quarter Waxing Gibbous Waxing Crescent

“Full” Moon When the Earth is between the moon & the sun, we see the full ‘lit’ side of the moon (we see a full circle – half the surface of the moon)

“Waning” Moon When the part of the moon we see lit by the sun is decreasing 3rd Quarter Waning Crescent Waning Gibbous

Then the cycle continues with a new moon…it’s been 29.5 days!

Using what you know of lunar phases, where is the sun in the picture above?

Earth and Moon Motions and Time Motions of the Earth and moon are frames of reference for determining time. Month = one cycle of moon phases (29.5 days) Day = one rotation of Earth (24 hours) Year = one revolution of Earth (365 days)

It takes the moon 27. 3 days to make a trip around the Earth It takes the moon 27.3 days to make a trip around the Earth. Then why is it 29.5 days between full moons?

It takes 27 days for the moon to orbit the Earth with respect to the stars. However, the Earth orbits around the sun as the moon orbits around the Earth, so the moon must ‘catch-up’. Thus it takes 29.5 days for the moon to reach the same position with respect to the Sun.

Eclipses Eclipse- when a celestial object partly or completely comes into the shadow of another celestial object Umbra: central area of full darkness Penumbra: area around the umbra of partial darkness

Eclipses Lunar eclipse- when the moon revolves into the shadow of the Earth at the FULL moon phase. Partial eclipse-part of the moon is covered Total eclipse- all of the moon is covered Average of 2 eclipses per year, 100 min long Seen by anyone on the night side of Earth When the Earth’s shadow falls on the moon, so we can’t see the moon NEXT ONE: Dec. 10, 2011 ~6:34am (partial @ moonset here) A total eclipse won’t be visible here ‘til Apr. 15, 2014

Dec 2011 Lunar Eclipse

Lunar Eclipse Winter Solstice Lunar Eclipse 2010 when the Earth’s shadow falls on the moon so we can’t see the moon Winter Solstice Lunar Eclipse 2010

Lunar Eclipse curved shadow straight shadow Phases of Moon

Eclipses Solar eclipse- when the moon blocks out the sun during the NEW moon phase Average of 1 every 200 years or so for a specific location, lasting 7.5 minutes Seen only by a small area on the day side Umbra: central area of full darkness Penumbra: area around the umbra of partial darkness When the moon’s shadow falls on the Earth & we don’t see the sun NEXT ONE HERE: Sep. 14, 2099 (total)

when the Moon’s shadow falls on the Earth and we don’t see the sun Solar Eclipse when the Moon’s shadow falls on the Earth and we don’t see the sun

Solar Eclipse