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Observing the Moon and Eclipses

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Lee Carkner's standard As311 template ... Astronomy 311 Professor Lee Carkner Lecture 4 Moon Basics Shows 1 complete set of phases in one month Phase is determined by ... – PowerPoint PPT presentation

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Title: Observing the Moon and Eclipses


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?
  • Moons 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
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