MOON

1
MOON ECLIPSES
2
(No Transcript)
3
Moons orbit viewed from above Earths north
pole

• Orbit period 27.3 days

(Sidereal Period)
4
Near Side
5
Far Side
6
MOTION OF THE MOON (Viewed from Earth)

• Diurnal (Daily) Motion East to West, relative
  to horizon rises sets
• Monthly Motion Eastward relative to stars
• due to orbit of moon about Earth

7
Orbit, viewed edge-on
Moons orbit plane
5o
Earths orbit plane
8
? Orbits tipped ? Orbit planes intersect along
Line of Nodes
p. 41
9
Viewed from Earth, moon moves 13o/day
9 pm
9 pm
9 pm
13o
13o
E S
W
10
Does the moon rotate?
11
(No Transcript)
12
(No Transcript)
13
The Lunar Phase Cycle
E
W
p. 39
14
Waxing Crescent
Horizon
West
toward sun
15
First Quarter
Horizon
South
16
Waxing Gibbous
Horizon
South
17
Full
Horizon
South
18
Waning Gibbous
Horizon
South
19
Third (Last) Quarter
Horizon
South
20
Waning Crescent
Horizon
East
toward sun
21

Phase Movie
E W
22
The Full Cycle
29.5 days One moonth
p. 39
23
(No Transcript)
24
Understanding the Phase Cycle
? Moon is always one-half illuminated.
Sunlight
?
? Just like Earth!
?? Phases result from viewing, from Earth,
fractions of illuminated half.
25
Moon
e.g., First Quarter
View from Earth
Sunlight
Earth
Result Moon appears one-half
illuminated
Note Not to scale
26
(No Transcript)
27
Phase Visibility
28
Eclipses

• Shadows
• gt Umbra Inner shadow
• gt Penumbra Outer shadow

p. 41
29
Lunar Eclipses
The moon was as though drenched with blood. - The
Anglo Saxon Chronicles (734 AD)

• Moon moves through Earths shadow
• Require
• gt Full Moon
• gt Moon along nodal line

30
The View from Space
Note not to scale
Maximum duration of totality ? 100 min
p. 42
31
The View from Earth
Duration 77 min
32
Partial Eclipse of July 28, 1999
33
Lunar eclipse occurs only when moon at/near
nodal line
No eclipse!
Eclipse
p. 41
34
From a vantage point in the plane of Earths
orbit . . .
5o
Earths shadow misses moon ? no eclipse!
35
What explains the color?
Earths shadow
Sunlight
Moon
Earth
Atmosphere

• Atmosphere bends (refracts) sunlight into umbra
• Atmosphere removes (scatters) blue/green part
• of light.

36
Eclipse of Jan 20 21, 2000
. . . the moon drenched with blood.
37
Solar Eclipses
And the moon in haste eclipsed her, and the Sun
in anger swore He would curl his wick within
him and give light to you no more. -
Aristophanes, Chorus of Clouds (423 BC)

• Earth intersects moons shadow
• Require
• gt New Moon
• gt Moon along nodal line
• Eclipse can be
• gt Total
• gt Partial
• gt Annular

38
Basic Geometry of Solar Eclipse
Umbra forms spot (diam 100 mi) on Earth
39
Another View
Partial eclipse seen in penumbra
Spot moves generally eastward at 1100 mi/hr,
creating zone of totality
p. 43
40
(No Transcript)
41
(No Transcript)
42
View from Earth Sun, totally eclipsed.
Solar Corona
?Maximum duration of totality 7.5 minutes
43
Sun, partially eclipsed
44
Moons orbit is not a circle . . .
45
Yielding Annular Eclipses

• Moons umbra does not reach Earth when
• moon too far away.

Earth
Moon
Sun
p. 43
46
Farthest
Closest
Ring or Annulus is seen when sun eclipsed.
Aug 24, 1998
47
How often do eclipses occur?

• Solar about twice per year, somewhere on
  Earth.
• gt At any given location, about once in 360 yrs.
• Lunar about twice per year.

48
Total Solar Eclipses 1997 - 2020
p. 44