Lecture 5 – The Moon
1
Motion of the Moon
Same face always kept towards earth.
Rotation period = Revolution period
Period = the time it takes to return to where
you started
2
Motion of the Moon
Sidereal Period = 27.3 days
Same face always kept towards earth.
Rotation period = Revolution period
Period = the time it takes to return to where
you started
Moon moves 13◦ /day in sky
Phases: Depends on relative position of sun
and moon.
Know when the moon rises and sets for Full,
New, and First and Last Quarter
3
Moon Rotation Period Tidally Locked
4
Lunar Phases
5
Lunar Phases
6
Lunar Phases at Sunset
7
Lunar Phases at Sunrise
8
Lunar Phases Quiz
Lunar Phase Quizzer
What Phase
(a) Full
(b) New
(c) First Quarter
(d) Third Quarter
(e) Waxing Gibbous
9
Sidereal Period vs Synodic Period
10
Tides I
Synodic Period (full moon to full moon) = 29.5
days
27 days to be in the same place with respect
to fixed stars but sun has moved 27◦ so 2
more days to catch up.
Tides: Differential pull of moon on different
parts of the earth.
11
Tides II
Spring Tides: High tide very high, low tide
very low.
Sun and moons pull adds so happens at new
and full moon
Neap Tides: High tide less high, low tide less
low.
Sun 90 degrees out of phase with moon, so
happens at first and third quarter moon.
12
Tides III
Friction causes rotation of earth to drag tidal
bulge ahead of earth-moon line, slowing
rotation of earth and leading to eventual loss
of the moon
Earth slows by 1.5 ms/century
Moon-earth distance increases by 4 cm/year
13
Moon pulls harder things near it
14
Spring Tides and Neap Tides
15
Friction slows earth rotation
16