Lunar Phases Eclipses

1
Today Moon Phases

2
Announcements

• The first homework due now.
• The next assignment is now posted
• due Tuesday, Feb. 6
• Weekly preceptor-led study group
• Every Monday 1030AM-1200Noon

3
Todays topics

• What causes moon phases?
• What is Earthshine?
• What causes eclipses?

4
The Phases of the Moon

• Key Points
• The Moon, at any time, is ½ illuminated by the
  Sun. The sunlit side always faces the Sun.
• The Moon orbits the Earth. As it does so, we see
  different fractions of the illuminated side.

? ? Sunlight ?
5
Nomenclature

• The Dark Side of the Moon
• This is the side that is not illuminated by the
  Sun.
• Note that this side of the Moon often faces us (a
  New Moon, for instance)
• The Far Side of the Moon
• This is the side of the Moon that is not facing
  the Earth
• We never see this side from Earth.
• Note that the Dark Side and Far Side are NOT the
  same
• except during a full moon ONLY

6
The New Moon

• When the Moon is between the Earth and Sun it
  is in the New Moon phase
• The New Moon rises at sunrise, sets at sunset,
  and is highest in the sky at noon (just like the
  Sun!)
• This is the best time to observe the stars in the
  night sky without the glare of the moon
  interfering dark skies

7

• The New Moon is the only time that a solar
  eclipse can occur

8
The Full Moon

• When the Moon is at opposition i.e on the
  opposite side of the Sun, we see the fully
  illuminated side. This is the Full Moon phase
• The Full Moon rises at sunset, sets at sunrise
  (exactly opposite to the Sun)
• This is the worst time to observe the stars in
  the night sky because of the Moons glare
• It is also not an ideal time to observe features
  on the moon through a telescope.

9

• The Full Moon phase is the only time in which a
  lunar eclipse can occur

10
The First-Quarter Moon

• When we see half of the sunlit side of the Moon
  it is said to be a quarter moon. If this occurs
  before the Full Moon (and after the New Moon)
  the phase is the First-Quarter Moon
• The First-Quarter Moon rises at noon, and sets at
  midnight.
• This is an excellent time to observe Moon
  features such as craters, rilles and rimae it
  is best to look along the terminator (the
  separator between light and dark)
• Go out shortly after sunset to get the best views
  (it is highest in the sky)

11
The Third-Quarter Moon

• If a quarter-moon phase occurs after the Full
  Moon (and before the New Moon) the phase is the
  Third-Quarter Moon
• The Third-Quarter Moon rises at midnight, and
  sets at noon.
• Just like the 1st-quarter Moon, this is an
  excellent time to observe moon features though a
  telescope.
• Go out just before sunrise (it is highest in the
  sky)

12
Waxing and Waning phases

• Waxing (increasing) is the term used to
  describe the phases after the New Moon and before
  the Full Moon
• During this phase, each day we see more and more
  of the illuminated side of the Moon
• Includes the first-quarter phase
• The beautiful crescent Moon seen just after
  sunset is in a waxing crescent phase
• Waning (decreasing) is the term used to
  describe the phases after the Full Moon and
  before the New Moon
• During this phase, each day we see less and less
  of the illuminated side of the Moon
• Includes the third-quarter phase
• The crescent Moon seen just before sunrise is in
  a waning crescent phase

May 3 May 1 April 29
This is an example of a waxing moon (it
increases with time)
13
Gibbous and Crescent
Gibbous Moon

• Gibbous means the full-ish phase which is when
  the Moon is between the 1st and 3rd quarter
  phases and we see more than half of the
  illuminated side of the Moon
• During the crescent phases we see less than half
  of the illuminated side of the Moon

Crescent Moon
14
(No Transcript)
15
Order of the Moon Phases

• (1. - start) New Moon
• dark skies !
• Moon is not visible (glare from the Sun)
• (2. - after a few days)
• Waxing crescent
• Sets shortly after sunset
• (3. - about 7 days) First Quarter Moon
• Actually a 1/2 moon
• Moon goes from a crescent to a gibbous moon
• (4. - about 14 days) Full Moon
• Goes from waxing to waning

• (5. - about 21 days) Third-Quarter moon
• Another ½ moon
• Waning phase
• Goes from gibbous to crescent
• (6. - about 26 days)
• Waning crescent
• Rises shortly before sunrise
• (1. - start again) New Moon

16
What is a Blue Moon?

• Two definitions
• (1) The second full moon within one calendar
  month
• (2) the 3rd full moon in a season that has 4
  full
• moons (huh?)
• From the Farmers Alamanc!
• The 4th is the Harvest Moon
• It is NOT BLUE !!

17
Todays topics

• What causes moon phases?
• What is Earthshine?
• What causes eclipses?

18
Earthshine
Dark side of the Moon, Illuminated by Earthshine
Sunlit side of the Moon
19

• Earthshine is due to the double reflection of
  sunlight.
• Light from the Sun is reflected off of the Earth
  (point A) onto the Moon (point B). Some of this
  light is then reflected off of the Moon back
  towards the Earth (point C).
• The brightest part of the Moon is illuminated by
  the Sun and the rest is dimly illuminated by this
  doubly reflected light.

20
Saturns moon Iapetus seen in Saturnshine
21
Todays topics

• What causes moon phases?
• What is Earthshine?
• What causes eclipses?

22
Eclipses

• Lunar Eclipses
• This occurs when the Earth shades the Moon as
  it passes between the Moon and Sun
• Total, Partial, Penumbral
• Occurs only during a full moon
• Solar Eclipses
• This occurs when the Moon passes in front of the
  Sun, blocking the Sun from view from Earth
• Annular, Total
• Occurs only during a new moon

Lunar Eclipse of 10/27/04 photo by
Instructor
23
Lunar Eclipses

• Does the moon become invisible?
• No, refraction of sunlight through the Earths
  atmosphere causes the moon to become reddish

24
Lunar Eclipse
25
Solar Eclipses
26
Total solar eclipse
27
Annular Solar Eclipse
28
Eclipses occur only when the Sun and Moonare
both on the line of nodes
29
Geometry and Path of Totality
30
Eclipse Paths
31
Reading for next class

• Chapter 5
• pp. 90-114 (you can omit section 5-8)

32
Extra slides
33
Guiding questions/concepts

• What causes moon phases?
• What is Earthshine?
• What is the difference between the synodic and
  sidereal month?
• What causes eclipses?

34
Guiding questions/concepts

• What causes moon phases?
• What is Earthshine?
• What is the difference between the synodic and
  sidereal month?
• What causes eclipses?

35
Guiding questions/concepts

• What causes moon phases?
• What is Earthshine?
• What is the difference between the synodic and
  sidereal month?
• What causes eclipses?

36
Time and the Moon

• Two types of months are used in describing the
  motion of the Moon.
• With respect to the stars, the Moon completes one
  orbit around the Earth in a sidereal month,
  averaging 27.32 days.
• The Moon completes one cycle of phases (one orbit
  around the Earth with respect to the Sun) in a
  synodic month, averaging 29.53 days.

37
Guiding questions/concepts

• What causes moon phases?
• What is Earthshine?
• What is the difference between the synodic and
  sidereal month?
• What causes eclipses?