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

2. 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

3. 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

4. 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

5. Phases of the Moon
Moon Phases activity
(cfp-5013)

6. 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

7. 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”

8. 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

9. 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

10. 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

11. Eclipses
Eclipse Activity:
(cfp-5013)

12. 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

13. 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

14. 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

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