G. 2003 Gonzalez
Lunar Phases -- The Movie
Lecture 7- Lunar phases
Phases of the Moon What causes them and what doesn't Phases of the Moon and time of day Lunar eclipses I
Lecture Challenge
A. What do you think causes the Moon to go through its phases?
Lunar Eclipse -- The Movie
The phases of the Moon.
Names of the lunar phases
Phases of the Moon's 29.5 day cycle
new crescent first quarter gibbous full gibbous last quarter crescent
waxing
waning
Lunar Eclipse -- The Movie
Gordon Garradd 1997
Lunar eclipses versus Lunar phases
How do these images differ? Note the different shapes of the Moon's terminator in the two images. Therefore, the Moon's phases and eclipses are due to two different phenomena, and the Moon does not go through its phases during an eclipse, nor visa versa.
Waxing Gibbous
Lunar Eclipse
Astro term: The terminator is the boundary between lit and dark regions.
Let's do an experiment
Let's consider the following model to explain the Moon's phases: the phases are due to the our changing perspective of a half-illuminated sphere. So, how do we test this idea?
Draw what you see...
What does this mean?
So far we learned that the Moon does not go though its phases during an eclipse and a changing perspective on a half-illuminated sphere can reproduce the observed phases. We can bring more information to bear on this:
-the Moon repeats its phases every 29.5 days. -the Moon completes an orbit in 27.33 days. -the phase depends on the angle between the Sun and Moon.
Last Quarter Waning Crescent Waning Moon
Full Gibbous
New Moon
Waxing Crescent First Quarter
Waxing Gibbous
Diagram above shows Earth-Moon system drawn to scale.
Sidereal vs. Synodic months
T=29.5d (Synodic) T=27.3d (Sidereal)
T=0d
New Moon
Test your understanding 1
Is there a "dark side" of the Moon?
The Moon always presents the same face to us. What does this imply?
Why do we see the same face?
Rotation period = orbital period
Moonrise & Moonset at 1st Quarter
Sunrise
Where is the Moon in the sky at sunset?
Midnight
Noon
N
Sunset
Note that the illuminated half of the Moon faces the Sun.
Sun's apparent path on the sky
June 21 E C.E. December 21 September 21 Ecliptic March 21
S
The New Moon's apparent path on the sky.
Moon's path
Ecliptic
Test your understanding 2
What does it mean to say that the Moon's path closely follows the ecliptic?
Test your understanding 3
You need to know how to answer questions of the foll...