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Motions of the Sky

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Motions of the Sky 1. Seasons 2. Tides 3. Moon Orbit/Tidal Locking 5. Moon Phases 6. Lunar Eclipses 7. Solar Eclipses 8. Planet Retrograde Motion – PowerPoint PPT presentation

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Title: Motions of the Sky


1
Motions of the Sky
1. Seasons 2. Tides 3. Moon Orbit/Tidal
Locking 5. Moon Phases 6. Lunar Eclipses 7. Solar
Eclipses 8. Planet Retrograde Motion
2
The Motion of the Earth
  • Rotation Spinning of the earth on its axis
  • 24 hours
  • 1 day
  • Revolution- movement of earth around the sun
  • 365 days
  • 1 year
  • Precession wobble of earth on axis
  • 26,000 years

3
Seasons
  • Seasons ARE NOT caused by the changing distance
    between the Sun and Earth.
  • During the Northern hemisphere winter, we are
    actually CLOSER to the Sun.

4
Seasons ARE caused by
  • The TILT of the Earth's axis.
  • The Earth is tilted 23.5 degrees

5
Seasons
When it is summer in one hemisphere, it is winter
in the other.
6
Apparent motion of the Sun
  • we do not perceive the Earth moving (Instead the
    sun appears to move.)
  • Ecliptic The apparent path of the sun

7
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8
Apparent Motion of the sun
  • Summer
  • more direct sunlight,
  • sun appears to be higher in the sky.
  • Higher on the ecliptic
  • Winter
  • less direct sunlight
  • sun appears to be lower in the sky.
  • Lower on the ecliptic

9
What Causes the seasons?
  • spring and fall
  • we get equal light as the opposite hemisphere.
  • (The sun in on the celestial equator).
  • Therefore, the seasons are determined by the suns
    position on the ecliptic.

10
Seasons
Summer Solstice - June 21 - 22. The sun is at
the highest point along the ecliptic. The first
day of summer and longest day of year.
11
Seasons
Summer Solstice - June 21 - 22. The sun is at
the highest point along the ecliptic. The first
day of summer and longest day of year. Fall
(Autumnal) Equinox - Sept. 22 - 23. The sun
crosses the celestial equator heading south. The
first day of fall. Equal length of day and
night.
12
Seasons
Summer Solstice - June 21 - 22. The sun is at
the highest point along the ecliptic. The first
day of summer and longest day of year. Fall
(Autumnal) Equinox - Sept. 22 - 23. The sun
crosses the celestial equator heading south. The
first day of fall. Equal length of day and
night. Winter Solstice - Dec. 21 - 22. The sun
reaches the lowest point on the celestial sphere.
The first day of winter and the shortest day of
the year.
13
Seasons
Summer Solstice - June 21 - 22. The sun is at
the highest point along the ecliptic. The first
day of summer and longest day of year. Fall
(Autumnal) Equinox - Sept. 22 - 23. The sun
crosses the celestial equator heading south. The
first day of fall. Equal length of day and
night. Winter Solstice - Dec. 21 - 22. The sun
reaches the lowest point on the celestial sphere.
The first day of winter and the shortest day of
the year. Spring (Vernal) Equinox - March 20 -
21. The sun crosses the celestial equator
heading north. The first day of Spring. Equal
length of day and night.
14
Seasons
15
Earth/Moon System
Scale Diagram of Earth/Moon System
16
What causes tides?
Just as the Earth pulls the Moon, the moon also
slightly pulls on the Earth.
17
Tides Basics
  • Tides
  • The moon pulls on everything on Earth.
  • since water is fluid, the Earth cannot hold onto
    it and the
  • moon is able to pull on it.
  • -This creates two tides per day.
  • (The continents are also pulled, but much less
    so, only about
  • 30 cm. This is not noticeable)

18
Tides
Tidal forces created by one large body on another
19
Sun Tides
Tides Caused by the Sun The Sun is also
pulling on the Earth, causing tides, but to a
much smaller extent
20
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21
Spring Tides
  • Spring Tides -When the Sun and Moon align, and
    the gravitational pull combine, we get extra high
    tides.

22
Neap Tides
Neap Tides -When the Sun and Moon are at right
angles, the gravitational pull cancels, and we
get extra small tides.
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27
Tides
The Bay of Fundy between Nova Scotia and Main
has the worlds most extreme tides. Tides can
raise and lower by 48 feet. http//www.youtube.c
om/watch?v_J2AtORivSY http//www.youtube.com/wat
ch?vSOAKZLwHhXU http//www.youtube.com/watch?vy
cNzUAp6OXk
28
Tides
29
Tides
  • Tidal forces causes
  • The Rotation of the Earth to slow down.
  • (This Causes Precession)
  • Length of day 6 hrs 4.5 billion years ago
    (formation of Earth)
  • Length of day 20 hrs 300 Million years ago
    (Devonian time period)
  • Length of day 23 hrs 80 million years ago
    (Cretaceous - Dinosaurs)
  • 2. The moon to drifting away.
  • It drifts away 4 cm a year, which is slowly
    increasing the length of the month.
  • (Verified by Mirrors placed on Moon during Apollo
    Missions)

3. Tidal Locking.
30
Tidal Locking (Phase Locking)
31
Tidal Locking (Phase Locking)
Tidal Locking Although the moon rotates AND
revolves, people on Earth only see 1 side of the
moon. Tidal locking causes 1 rotation of the
moon to be equal to 1 revolution of the moon
(1 rotation 1 revolution)..
32
Tidal Locking (Phase Locking)
33
Tidal Locking (Phase Locking)
Tidal locking is normal. Objects that are tidally
locked Moon to Earth Phobos and Deimos to
Mars Most of Jupiter and Saturn's Moons. Pluto
and Charon Probably Neptune's and Uranus's moons
(not enough data) Mercury to the Sun
34
The Moon
  • The moons orbit is not circular, it is
    elliptical.
  • This means the moons distance from earth changes
    over the course of a month.

35
Moon Distance Perigee vs Apogee
36
Perigee and Apogee
37
Moon Distance Perigee vs Apogee
Scale diagram of Earth/Moon system
38
The Moon at Perigee and Apogee
Perigee - The moons closest approach to earth.
(356,000 km) Apogee - The moons farthest
distance from earth. (407,000 km)
39
Moon Phases
40
Moon Phases
Caused by the angle at which we view the moon as
it orbits the Earth.
41
Moon Phases
  • What is happening
  • The sun always shines on 1/2 of the moon.
  • Depending on the angle at which we see the moon,
  • we see different parts of the moon lit up at
    different times.

42
Moon Phases
43
Moon Phases
44
Moon Phases
45
Lunar Eclipses
46
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47
Cause of Eclipses
48
Cause of Eclipses
49
Lunar Eclipse Occurs when the moon passes
through the Earths shadow. This only occurs
during a FULL moon phase, twice per year.
50
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51
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52
Lunar Eclipses
53
Lunar Eclipse Terminology
Umbra The central, dark, shadow of the Earth.
Penumbra - The outer, lighter, shadow of the
Earth.
54
Drawing
55
Lunar Eclipse Terminology
Total Eclipse - The entire moon enters the
Earths Umbra. Partial Eclipse Only part of
the moon enters the Earths Umbra.
56
Lunar Eclipse Terminology
Partial Eclipse
Total Eclipse
57
Why is the moon RED during total lunar eclipses?
  • Only light scattered through the Earths
  • atmosphere strikes the moon. This
  • scattered light is red. (same reason why
  • sunsets/rises look red.

58
Lunar Eclipse Pictures
59
Lunar Eclipse Pictures
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61
Solar Eclipses
62
Solar Eclipses
63
Solar Eclipse Terminology
Solar Eclipse - When the moon passes directly
between the Sun and Earth, the moons shadow will
strike the Earth. This only occurs during a NEW
Moon phase, approximately twice per year.
64
Why are Total Solar Eclipses much less common?
65
Animated Solar Eclipse as seen from Space

Notice the tiny size of the moons Umbra
66
Solar Eclipses as seen from Space
67
Solar Eclipses as seen from Space
From a weather satellite
68
Solar Eclipse Terminology
  • Total
  • B. Annular
  • C. Partial

69
Solar Eclipse Terminology
Total Eclipse - The Umbra of the moon strikes
the Earth. Anyone standing in this spot sees the
moon completely covering the Sun.
70
Solar Eclipse Terminology
Corona The faint outer atmosphere of the Sun.
Only visible during Total eclipses.
Antarctic Total Eclipse
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73
Solar Eclipse Terminology
Partial Eclipse The Penumbra of the moons
shadow strikes the Earth. Anyone standing in
this Spot sees the moon partially covering the
Sun.
74
Solar Eclipse Terminology
Annular Eclipse The moon passes directly in
front of the Sun. However, the moon is at
Apogee, and looks too small to cover the sun for
a Total eclipse.
75
Solar Eclipse Terminology
Ring of Fire During an Annular eclipse, the sun
appears to be a ring surrounding the moon.
76
Annular Eclipse
77
Annular Eclipse
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79
Retrograde Motion
Retrograde Motion Planets generally move from
west to east in the sky. Occasionally, a planet
will seem to slow down, stop, and loop backwards
for a short time.
80
Retrograde Motion of Mars
81
Retrograde Motion
Retrograde Motion Planets generally move from
west to east in the sky. Occasionally, a planet
will seem to slow down, stop, and loop backwards
for a short time. Reason Why The planet did
not physically stop and move backward. This
illusion is created by the fact that one of the
planets passed the other in orbit. (Similar to
passing a car on a highway, the car being passed
appears to move backward)
82
Retrograde Motion
83
Retrograde Motion of Venus
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