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The
Earth/Moon/Sun
System
Planet Earth
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40,000 km (25,000 mi.) in circumference
13,000 km. (8,000 mi.) diameter.
Bulges slightly at equator.
150 million km (93,000,000 mi.) from Sun.
Has magnetic field called magnetosphere
(generated by our core) that shields us from
the solar wind and some harmful radiation.
Earth’s Movements
• rotation
– spinning on axis
– completes one
rotation in 23 hrs,
56 minutes
Earth’s Movements
• revolution
– orbiting sun
– completes one revolution in 365.26 days
• precession
– direction of axis moves, like a spinning top
– period = 26,000 years
The Right-Hand Rule
If the thumb of your right hand represents the
North Pole, the earth rotates in the direction that
your fingers point (west to east).
Apparent
Movement
•The rotation of the
Earth makes objects
(sun, moon, stars)
appear to move across
our sky from East to
West.
•Stars between the
North Star and the
horizon never set, and
are called circumpolar.
Sidereal Day vs. Solar Day
• Sidereal Day - 23
hrs., 56 minutes – time
it takes Earth to make
one complete rotation
(a distant star returns
to the same position in
the sky).
• Solar Day – 24 hours,
time it takes for the
sun to return to the
same position in the
sky. (4 minutes longer
than sidereal day)
Seasons
• Earth’s axis is tilted 23.5°.
• Axis always points to same direction in space.
• Amount of sunlight falling on different regions
changes throughout year.
• Northern hemisphere is tilted towards sun in
summer, away in winter. Animations
Reasons for Seasons
• Summer – Sun passes through less atmosphere at a more direct
angle (more concentrated) for a longer portion of the day.
•Winter – Sun passes through more atmosphere at a less direct angle
(less concentrated) for fewer hours per day.
Solstices – “sun stands still”
• Summer Solstice – usually June 21
– First day of summer.
– Longest daylight period and shortest night in northern
hemisphere.
– Sun directly overhead at noon at Tropic of Cancer
(23.5o N).
• Winter Solstice – usually December 21
– First day of winter.
– Shortest day daylight period and longest night.
– Sun directly overhead at noon at Tropic of Capricorn
(23.5o S).
http://www.physicalgeography.net/fundamentals/6h.html
Seasons Explained
Seasons Explained 2
•The tilt of the axis also determines the Arctic Circle (66.5o N)
around the North Pole, in which there is 24 hours of daylight on
the Summer Solstice and 24 hours of night on Winter solstice.
•Antarctic Circle (66.5o S) around the South Pole has the
opposite pattern.
Equinoxes – “equal night”
• Equal day and night length (12 hours each).
• Sun is directly overhead at the Equator.
– Vernal Equinox - first day of spring, usually
March 21.
– Autumnal Equinox - first day of autumn,
usually September 21.
http://www.physicalgeography.net/fundamentals/6h.html
Seasons Explained
Seasons Explained 2
Orientation of the Earth’s axis relative to the Sun makes
the sun appear higher in the sky in summer (when we’re
tilted toward it) and lower in winter (when we’re tilted
away. Celestial Sphere and the Sun's Path
http://www.physicalgeography.net/fundamentals/6h.html
Seasons Explained
Seasons Explained 2
Time Zones
Longitude & Time Zones
Time Zones Explained
More Time Zones
• Local noon is when sun crosses our meridian.
• Local time varies continuously with longitude.
• Standard time zones were invented to avoid
confusion.
• International Date Line
– gain day going east (subtract 1 day from date,
repeat day)
– lose day going west (add 1 day to date from
eastern side) International Date Line Explained
Earth’s Moon
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No atmosphere.
No magnetic field.
Small iron core.
Unusually large compared to Earth.
Many craters visible because the moon has
no plate tectonics, atmosphere, weathering,
or erosion.
• Completes revolution and rotation in 27.3
days, so same side always faces earth.
• Full moons 29 days apart.
Sidereal Month – 27 1/3 days, time it takes the moon
to make one complete revolution around Earth.
Synodic Month – 29 ½ days, time it takes the moon to
complete one lunar cycle (new moon to new moon).
Synodic Month vs. Sidereal Month Animation
• Highlands – lightcolored, mountainous
regions, original terrain.
• Maria – dark-colored
lowlands where basaltic
magma leaked out and
flood area. Moon
• Regolith – layer of
pulverized material from
meteorite impacts.
Lunar Features
Origin of the Moon
• Early in life of solar system, Mars-sized planet
struck Earth with a glancing blow.
• Knocked off mostly lower-density rock from the
crust/mantle, little of iron core.
• Ejected material remained
in orbit, pulled
together by
gravity.
Moon
Moon Phases
• Half of moon is always lit by sun.
• How much of lit half we see depends upon
relative positions of sun, earth, and moon.
• Full moon - moon is on opposite side of
earth from sun, rises as sun sets, we see
entire lit side.
• New moon - moon is lined up on same side
as sun, rises & sets with sun, we can’t see it.
Moon Phases
• Waxing – lit portion of the moon gets
bigger each day, lit on the right side.
• Waning – lit portion of the moon gets
smaller each day, lit on the left side.
• Crescent – less than half of the moon’s face
is lit (excluding new moon).
• Gibbous – more than half of the moon’s
face is lit (excluding full moon).
Eclipses
• Lunar Eclipse - moon moves into earth’s
shadow. SunEarthMoon
• Partial shadow (penumbra) darkens moon
slightly, full shadow (umbra) takes “bite” out of
moon & gives shadowed surface a reddish glow.
•
Earth & Moon Shadows
What would a “solar” eclipse
look like from the moon?
• It looks like
this! One would
essentially see
all of the
sunrises and
sunsets on Earth
simultaneously.
Eclipses
• Solar Eclipse - earth moves into moon’s shadow.
SunMoonEarth
• Only a portion of Earth sees partial eclipse
(penumbra), tiny portion sees total eclipse
(umbra) Earth and Moon Shadows
• Eclipses don’t happen every month because plane of moon’s
orbit is tilted (moon is usually above or below the Earth’s
shadow). Moon's Orbital Tilt
Eclipse Table
• Because of this and Earth’s axial tilt, the moon’s path (and
full moon) is higher in our winter when the Northern
Hemisphere is tilted away from the sun (toward full moon).
Full Moon Declination Table
Tides
• Caused by gravitational pulls of sun and moon.
• Moon’s influence is greater (less mass, but
much closer).
• Spring Tides (extreme) occur when earth, sun,
and moon are in line (full & new moons).
• Neap Tides (reduced) occur when sun’s and
moon’s pull are at right angles (first and last
quarters). Do We Really Need the Moon?
Tidal Bulge Simulator
Highest High Tides in the World
http://www.youtube.com/watch?v=qfhNjpu_IU4 -
Bulge of water at
high tide is
funneled into
increasingly
narrow bays.
Highest tides are
at the far end of
the Bay of
Fundy.
Incoming tide
often appears as a
rolling wave
moving up the
bay, called a tidal
bore.
Tidal Bore
In a confined bay, such as the Bay of Fundy, the incoming
tide forms a standing wave that rushes into the bay.
Tidal Bore Turnagain Arm, Alaska
Standup Paddleboard Tidal Bore Surfing
Knik Arm Bore Tide
Tidal Bore Nova Scotia
Bay of Fundy Tidal Bore rafting
Turnagain Arm of Cook Inlet,
Alaska
Atmospheric Astronomy
Auroras
Aurora Borealis – Northern Lights
NG Northern Lights
Northern Lights
Northern Lights - short
Aurora Australis – Southern Lights
Cause: Sun emits
constant stream of
charged particles –
solar wind, solar
flares, coronal mass
ejections (CMEs).
Earth’s magnetic field
shields us from most,
funnels charged
particles into
atmosphere around
north & south
magnetic poles.
Auroras
Auroras
In upper atmosphere (thermosphere, ionosphere), charged
particles interact with atmospheric gases to emit light.
Nitrogen – blue or purplish-red
Low altitude (100-300 km) oxygen – yellowish-green
High altitude (>300 km) oxygen – red (rare)
Very low altitude (100 km) nitrogen – reddish fringe on bottom
of “curtains”
High altitude hydrogen & helium – deep blues & purples
Auroras
Northern
Lights
Tourism
Meteors
• Solid space debris (meteoroids) penetrate atmosphere & ignite
due to friction (meteors).
• Any that survive plunge & land on Earth are meteorites.
Meteorites
• Stony – mineral crystal
composition (silica)
similar to some earth
rocks.
• Iron – mostly iron w 530% nickel
• Stony-iron – blend of
the two previous
• Lunar
• Martian
Fireballs – Large space rocks entering atmosphere at shallow angle,
often disintegrate or explode.
Tunguska
Event - 1908