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Understanding Lunar Phases and Eclipses for Astronomical Observations

Dive into the fascinating world of lunar phases and eclipses, exploring the reasons behind their occurrence and their significance in ancient civilizations. Learn about the Moon's motion, phases, eclipses, and their predictability. Discover the complexities of eclipses and the unique phenomena associated with lunar and solar events.

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Understanding Lunar Phases and Eclipses for Astronomical Observations

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  1. Assign. #1 distributed Friday Sep. 15. Due in your lab section slot, by 5 PM Sep 23. Office hours Mon, Thurs, and Friday this week. See Web page. Lab 1 will be due between Sep. 25 - 28. The motion of the Moon • ANNOUNCEMENTS

  2. The Moon, Our Constant Companion Our goals for learning: • Why do we see phases of the Moon? • What conditions are necessary for an eclipse? • Why were eclipses difficult for ancient peoples to predict ? Note: the Chpt. 2 Moon tutorial on masteringastronomy.com is useful!

  3. Animations • Ecliptic Plane • Orbit of Moon

  4. Why do we see the same face? Rotation period = orbital period What do you see if you're standing on the Moon looking at Earth?

  5. Animations • Causes of lunar phases

  6. Lunar Motion Phases of the Moon’s 29.5 day cycle (is that synodic or sidereal???) • new • Crescent • first quarter • gibbous • full • gibbous • last quarter • crescent Waxing Waning

  7. The lunar phases • Notice that the size seems to change. Why? • Notice that it 'wobbles' a bit. Why?

  8. The lunar phases • Notice that the size seems to change. Why? • Moon is not at a constant distance. • Notice that it 'wobbles' a bit. Why? • Because the orbital speed is not exactly constant • Called 'librations'

  9. Why do we see phases? • Half the Moon illuminated by Sun and half dark • We see some combination of the bright and dark faces

  10. Preliminaries: Local Solar time Interactive applet at mastering astronomy .com

  11. Phases of the Moon. An example: the waxing crescent From the publisher's web site.

  12. Rising/setting times of the Moon • Depending on the phase of the Moon it always rises and sets at the same (rough) local solar time. • This is due to simple geometry of the illumination by the Sun. See Fig 2.21 of Cosmic Perspective. NOTE: The times above neglect the Earth's tilt!

  13. Animations • Phases of the Moon • Rise/set time vs phase • Handout given in class

  14. Q: You see a quarter moon rising after drinking in the Pit. What time is it? • 9 PM • Midnight • 3 AM • 6 AM Bonus : First or Third quarter?

  15. Eclipses : Puzzles for ancient astronomers/astrologers • The Earth & Moon cast shadows. • When either passes through the other’s shadow, we have an eclipse. • Why don’t we have an eclipse every full & new Moon? Eclipses twice a month?

  16. The Moon's orbit is inclined. • Moon not necessarily in the ecliptic when it comes `into line' with the Sun

  17. Animations • Moon's orbit tilt • Eclipse Seasons... • How rare are eclipses

  18. Eclipse Predictions • Eclipses recur in the approx. 18 yr, 11 1/3 day saros cycle • But even then, eclipse location and type (e.g., partial, total) may vary. Why?

  19. Lunar Eclipses (way out of scale) From the publisher's web site.

  20. Lunar Eclipse Sequence Is time going L to R or R to L ?????

  21. Lunar eclipse geometry

  22. Solar eclipse geometries • Total • Partial • Annular

  23. Does time go from right to left or left to right here? Time-lapse photo taken in northern Europe

  24. Solar Eclipses Animation

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