1. Observing the Moon and Eclipses Astronomy 311 Professor Lee Carkner Lecture 4

2. Moon Basics  Moon orbits the Earth once every ~30 days (1 month)   1/2 of the moon is always lit by the Sun 

3. Moon Phases  New --  Quarter –  Full –  Crescent –  Gibbous –  Waxing –  Waning –

4. Phases of the Moon

5. Sidereal and Synodic  Sidereal period -- time for moon to return to initial position with respect to the stars (27.32 days)   Synodic period -- time for moon to return to initial position with respect to the sun (29.53 days) 

6. Why is a Synodic Month Longer than a Sidereal Month?

7. Where is the Moon?  The moon makes one orbit in about 30 days   Moon’s orbit moves it west to east   Moon rises about 45 minutes later each night

8. Eclipses  Solar Eclipse    Lunar Eclipse   Happens during Full moon

9. When do Eclipses Happen?  Why aren’t there eclipses every new and full moon?   Only have eclipses when Sun falls on line of nodes (line where the orbital plane of the Earth and Moon intersect)

10. Line of Nodes

11. Shadows  Umbra -- Darkest part of the shadow   Penumbra -- Less dark part of shadow, region is still getting some sunlight   Penumbral eclipses can be hard to notice

12. Geometry of a Lunar Eclipse

13. Types of Lunar Eclipses  Total Eclipse -- Moon is completely covered   Partial -- Moon is partially covered   Penumbral -- only the penumbra covers the Moon  You can still faintly see the Moon even during a total lunar eclipse because of scattered light (circular sunset)

14. Lunar Eclipse

15. Types of Solar Eclipses  Total Eclipse -- Sun is completely covered   Partial -- Sun is partially covered 

16. Total Solar Eclipse

17. Diamond Ring Effect

18. Solar Eclipse in Action

19. Annular Eclipse  Moon is about 400 times smaller than the Sun, but is also about 400 times closer   When the Moon is the furthest from the Earth it does not completely cover the Sun  Annular Eclipse --

20. Annular Eclipse

21. Solar Eclipse from Space

22. Partial Solar Eclipse Christmas 2000

23. Next Eclipses  Eclipses visible from central U.S.    Lunar eclipses are visible from the entire night side of the Earth, but the shadow of the Moon only covers a small fraction of the Earth’s surface 

24. Summary  Orbit  one complete orbit in one sidereal month  same side always faces the Earth  Phases  complete set in one synodic month  where the Moon is in sky at a particular time depends on the phase

25.  Eclipses  caused by Earth or Moon blocking out the Sun  only occur when line of nodes points at Sun  are darkest when in the umbra  occur in cycles

26. Next Time  Read chapter 2.5-2.7 for next time