Phases, Eclipses, & Tides Chapter 1, Section 3, p20-27

Motions of the Moon Moon moves through space in two ways Revolves around Earth Relative positions of sun, Earth, and moon change The changing relative positions of the moon, Earth, and sun cause the phases of the moon, eclipses, and tides Rotates on its axis 1 moon “day” = 1 moon “year” Time to rotate once is same as time to revolve around Earth Same side of moon always faces Earth

Phases of the Moon Moonlight is reflected sunlight Moon doesn’t give off own light Able to see things in dark room when light bounces off them to your eyes Phases: different shapes of the moon you see from Earth One phase cycle = one revolution of moon around Earth

Phases of the Moon Moon phases caused by changes in relative positions of sun, Earth, and moon Half of the moon always lit Moon revolves around Earth We see the moon from different angles The side of the moon we see, isn’t always the “lit” side The phase of the moon you see depends on how much of the sunlit side of the moon faces Earth New moon – side of moon facing Earth isn’t lit (sun behind moon) Full moon – side of moon facing Earth is lit (sun in front of moon) Cycle ≈ 29.5 days

Phases of the Moon Moon Phases activity www.PHSchool.com (cfp-5013)

Eclipses Eclipses Eclipse: when a space object moves between the sun and a third object casting a shadow on that third object When the moon’s shadow hits Earth, or the Earth’s shadow hits the moon, an eclipse occurs Moon’s orbit is slightly tilted with respect to Earth’s orbit Moon revolves around Earth without moving into Earth’s shadow or casting a shadow on Earth

Eclipses When Do Solar Eclipses Occur A solar eclipse occurs when the moon passes directly between Earth and the sun, blocking sunlight from Earth Solar eclipse: new moon blocks your view of the sun Solar – Latin word for “sun”

Eclipses Total Solar Eclipses Partial Solar Eclipses Umbra: darkest part of shadow; (cone-shaped) From any part in umbra light is completely blocked Moon’s shadow just long enough to reach Earth Only few people on Earth in umbra experience total solar eclipse Sky grows dark as night Air becomes cool Able to see stars and solar corona (outer atmosphere of sun) Partial Solar Eclipses Penumbra: part of shadow less dark than the umbra; (larger part of shadow) From any part in penumbra light is partial blocked Part of sun is still visible – don’t look at sun

Eclipses When Do Lunar Eclipses Occur During a lunar eclipse, Earth blocks sunlight from reaching the moon Lunar eclipse: full moon is in Earth’s shadow and looks dim

Eclipses Total Lunar Eclipses Partial Lunar Eclipses Umbra: darkest part of shadow Total lunar eclipse occurs when moon is in Earth’s umbra Able to see Earth’s shadow on moon before and after eclipse Able to be seen anywhere on Earth that moon is visible Partial Lunar Eclipses Partial lunar eclipse occurs when moon passes partly into umbra of Earth’s shadow

Eclipses Eclipse Activity: www.PHSchool.com (cfp-5013)

Tides Tides Tides: the rise and fall of ocean water that occurs every 12.5 hours or so Cycle: Water rises ≈ 6 hours Water falls ≈ 6 hours Tides are caused by differences in how much the moon’s gravity pulls on different parts of Earth

Tides Tide Cycle Figure 16 Moon’s gravitational pull exerts a force Strongest on water closest to the moon Water flows towards this point = high tide Pulls on Earth more than water on far side of Earth Weakest on water farthest from the moon In between these two points are low tides Water flows away from these areas

Tides Spring Tides Neap Tides Spring tide: tide with the greatest difference between consecutive low and high tides Occur twice a month when sun and moon are in a straight line Full moon New moon Neap Tides Neap tide: tide with the least difference between consecutive high and low tides Occur twice a month when sun and moon pull at right angles 1st Quarter moon 3rd quarter moon

Homework Read Section 3: p20-27 Answer ?s 1-3 p27