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

2. Moon Basics   Shows 1 complete set of phases in one month   Phase is determined by how much of the lit side we can see

3.  New --  Quarter -- see 1/2 illuminated side  Full --  Crescent --  Gibbous -- more than 1/2 of illuminated side  Waxing --  Waning -- decreasing brightness

4. Sidereal and Synodic  Sidereal period -- time for moon to return to initial position with respect to the stars (27.3 days)   Synodic period -- time for moon to return to initial position with respect to the sun (29.5 days) 

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

6. Where is the Moon?  Since the moon makes one orbit in about 30 days, it moves 1/30 of a complete circle in the sky in one day   Moon is ~12 degrees further east each night 

7. Eclipses  Solar Eclipse   Happens during New moon  Lunar Eclipse   Happens during Full moon

8. When do Eclipses Happen?   Moon’s orbit is tilted by about 5 degrees with respect to the ecliptic (plane of the Sun and Earth)  Only have eclipses when Sun falls on line of nodes (line where the orbital plane of the Earth and Moon intersect)

9. Line of Nodes

10. Shadows on the Moon  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

11. Geometry of a Lunar Eclipse

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

13. Lunar Eclipse

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

15. 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 --

16. Annular Eclipse

17. Solar Eclipse from Space

18. Next Eclipses  Eclipses visible from central U.S.  Lunar –  Total solar eclipse – August 21, 2017   For any given location, you see many more lunar than solar eclipses

19. Next Time  Read chapter 2.5-2.8 for next time

20. 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

21.  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