Movements of the Moon

1. Movements of the Moon Ch. 28

2. Earth – Moon System • Earth and moon revolve around each other. • The balance point of the Earth-moon system is located within the Earth’s interior, because Earth’s mass is greater than the moon’s mass. • Barycenter – balance point. Follows a smooth orbit around the sun.

3. Moon’s Elliptical Orbit • apogee in the orbit of a satellite, the point at which the satellite is farthest from Earth • When the moon is farthest from Earth, the moon is at apogee. • perigee in the orbit of a satellite, the point at which the satellite is closest to Earth • When the moon is closest to Earth, the moon is at perigee.

4. Question? • Do you think moons orbit is a circle or an ellipse around the Earth??? • Ellipse!

6. Moonrise and Moonset • Why does it appear that the moon rises and sets each night? • Because of Earth’s rotation on its axis • The moon rises and sets 50 minutes later each night. This happens because of both Earth’s rotation and the moon’s revolution. • While Earth completes one rotation each day, the moon also moves in its orbit around Earth. It takes 1/29 of Earth’s rotation, or about 50 minutes, for the horizon to catch up to the moon

7. Lunar Rotation • The moon’s revolution around Earth and its rotation on its axis take the same amount of time • This is why we always see the same side of the moon.

8. Question?? • So, why are we unable to photograph the far side of the moon?? The far side of the moon is never visible from Earth, because the moon’s rotation and the moon’s revolution around Earth takes the same amount of time.

9. Eclipse • eclipse an event in which the shadow of one celestial body falls on another • Shadows cast by Earth and the moon have two parts: • Umbra – the inner, cone-shaped part of the shadow • Penumbra – the outer part of the shadow

10. Solar Eclipses • solar eclipse the passing of the moon between Earth and the sun; during a solar eclipse, the shadow of the moon falls on Earth.

11. Solar Eclipses • http://www.cbsnews.com/video/watch/?id=6100735n

12. Solar Eclipses • The umbra falls on the area of Earth that lies directly in line with the moon and the sun. • Outside the umbra, but within the penumbra, people see a partial solar eclipse. The penumbra falls on the area that immediately surrounds the umbra.

13. Total and Annual Eclipse • What is the difference between a total eclipse and an annal eclipse? • If the moon is at or near apogee (farthest of from the sun) during a solar eclipse, the moon’s umbra does not reach Earth. This causes an “annual eclipse” in which a thin ring of sunlight is visible around the outer edge of the moon. • The brightness of this ring prevents observers from seeing the outer layers of the sun’s atmosphere.

14. Annular Eclipse Total Eclipse

15. Question???? • What is one difference between a total solar eclipse and an annular eclipse? • During a total eclipse, the entire disk of the sun is blocked, and the outer layers of the sun become visible. During an annular eclipse, the disk of the sun is never completely blocked out, so the sun is too bright for observers on earth to see the outer layers of the sun’s atmosphere.

16. Lunar Eclipses • lunar eclipse the passing of the moon through Earth’s shadow at full moon • A lunar eclipse occurs when Earth is positioned between the moon and the sun and when Earth’s shadow crosses the lighted half of the moon. • Partial lunar eclipse – when only part of the moon passes into Earth’s umbra • Penumbral eclipse – when the entire moon passes through Earth’s penumbra

17. Lunar Eclipse

18. Partial eclipse Total eclipse

19. Solar and Lunar Eclipses

20. Review??? • What is the difference between a solar eclipse and a lunar eclipse?? • The point in the orbit of a satellite at which the satellite is farthest from Earth is the satellite’s • Apogee • Perigee • Baycenter • phase APOGEE

21. Review… 3. When the moon is at its apogee, what part of its shadow cannot reach Earth during an eclipse? Umbra

22. Phases of the Moon • phase in astronomy, the change in the illuminated area of one celestial body as seen from another celestial body • phases of the moon are caused by the changing positions of Earth, the sun, and the moon

23. Phases of the Moon - Waxing • When the size of the lighted part of the moon is increasing, the moon is said to be waxing. • When a sliver of the moon’s near side is illuminated, the moon enters its waxing-crescent phase. • When a waxing moon becomes a semicircle, the moon enters its first-quarter phase. • When the lighted part of the moon’s near side is larger than a semicircle, the moon is in its waxing-gibbous phase. • At full moon, the entire near side of the moon is illuminated by the light of the sun.

24. Waxing Moon Phase

25. Waxing Con’t

26. Waning Moon Phase • When the lighted part of the near side of the moon appears to decrease in size, the moon is waning. • When the moon is waning, but is still larger than a semicircle, the moon is in the waning-gibbous phase. • When the moon is waning, and it is a semicircle, the moon enters the last-quarter phase. • When only a sliver of the near side is visible, the moon enter the waning-crescent phase. After this phase, the moon becomes a new moon, in which no lighted area of the moon is visible from Earth.

27. Waning Moon Phase

28. Which one is it???

29. Moon A • What do you expect the Moon A in the picture to do during the next few days? Will the lighted part get bigger (wax) or get smaller (wane)? • The diagram shows the lighted part of Moon A decreasing from November 8 to November 12. This means the Moon is waning.

30. Moon B • What do you expect the Moon B in the picture above to do during the next few days? Will the lighted part get bigger (wax) or get smaller (wane)? • Look at the terminator for the Moon on day 1. Which way does the terminator move from day 1 to day 7? • While this is all imaginary ideas, the one true fact is that the Moon’s terminator always progresses from right to left across the Moon Disk in the sky.

31. Time from new moon to new moon • The moon revolves around Earth in 27.3 days, however, the period from one new moon to the next one is 29.5 days. • This difference of 2.2 days is due to the orbiting of the Earth-moon system around the sun. • In the 27.3 days in which the moon orbits Earth, the two bodies move slightly farther along their orbit around the sun. So, the moon must go a little farther to be directly between Earth and the sun. About 2.2 days are needed for the moon to travel this extra distance.

33. Question? • What is the difference between waxing and waning of the moon? • Waxing, the moon is growing – getting bigger into a full moon • Waning, the moon is getting smaller – going toward a new moon