The Moon (Phases, Eclipses, and Tides)
Our Motion & the Moon Nutation Barycenter Nutation and Precession
What makes our Moon weird? Large in comparison to the planet that it orbits 27% the radius of Earth Great distance from Earth (most moons are closer) Solid rocky composition (most are icy)
Moon Vs. Earth The moon can get reallllllly hot and cold (127°C, -173°C), but because it has no atmosphere, it does not retain heat in the absence of sunlight No erosion (no wind or water) Areas of high elevation (highlands) and low elevations (maria and craters) Very similar mineral content Differences Similarities
How was the Moon formed? Capture Theory: As the solar system was forming, an object came too close to the forming Earth and got sucked into our gravitational pull Simultaneous Formation Theory: The moon and Earth formed at the same time and in the same area (that’s why the compositions are similar) Impact Theory: The moon formed as a result of the collision of Earth and a Mars-sized object about 4.5 billion years ago. Debris from both merged together to form the moon (most widely accepted!)
Phases, Eclipses, & Tides The moon is Earth’s closest neighbor out in space at 384,400 kilometers out in space or 30 Earths lined up in a row. The moon revolves around the Earth as the Earth revolves around the sun. The positions of the moon, Earth, & the sun cause the phases of the moon, eclipses, and tides.
Motions of the Moon: As the moon revolves around the Earth it rotates on its own axis; its orbit similar to Earth’s as a flat oval, tilted at about 7˚. The moon takes about 27.3 days to orbit around the Earth; it also takes 27.3 days to complete one revolution on its own axis causing a moon “day” & a moon “year” to be the same length of time. The moon & Earth have synchronous rotation, meaning the same side of the moon always faces Earth. The “far side” of the moon always faces away from Earth & is never seen.
Phases of the Moon: The moon does not produce its own light, instead it reflects the light from the sun. The moon has 8 phases and goes through the whole set once a month, or 29.5 days. What Causes Phases? The phase of the moon you see depends on how much of the sunlit side of the moon faces Earth.
The Cycles of the Phases: From one full moon to the next it takes about 29.5 days. The 8 phases of the moon in order are: New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Third Quarter, Waning Crescent.
Eclipses When the moon’s shadow hits Earth or Earth’s shadow hits the moon, an eclipse occurs. There are 2 types of eclipses: solar (sun) eclipse & lunar (moon) eclipse. The type of eclipse is named for what is being blocked from Earth. Total solar eclipse Total lunar eclipse
Solar Eclipse The umbra is the darkest and smallest part of the shadow & is cone shaped (total darkness). The penumbra is the largest part of the shadow (partial darkness). Total Solar Eclipse: Only people in the umbra experience a total solar eclipse. Partial Solar Eclipse: In the penumbra, people only see a partial eclipse; since part of the sun is still visible, it is not safe to look directly at the eclipse.
Lunar Eclipse Total Lunar Eclipse During a full moon the Earth blocks the sun’s light from reaching the moon making the moon look dark from Earth. Total Lunar Eclipse When the moon is in the Earth’s umbra, there is a total lunar eclipse Partial Lunar Eclipse The moon passes partly into the umbra of the Earth’s shadow.
The Tide Cycle The moon’s gravity pulls Earth’s water toward itself and away from 2 opposite places, creating low tides. All 4 tides rotate in a 25 hour cycle.
Spring & Neap Tides Spring tides occur twice a month, one at full moon & one at new moon. The combined force of the sun & moons gravity make a tide with the most intense high & low tide. Neap tides happen 2 times a month, one at first quarter moon & one at third quarter moon. The sun & Earth are at right angles and creates tides with the least intense difference between high & low. (It’s like a tug-of-war between the moon and sun).