The Motion of the Moon The Moon The Earth, Sun, and Time of Day

Astronomy 310 (Newbury)
May 15, 2007
The Motion
of the Moon
Section 1.6
The Moon
Earth has one natural satellite, the Moon.
It orbits the Earth about once a moonth at
a distance of 384 000 km. The Moon’s
diameter is 3476 km or 0.27 D E (Earth
diameters).
As the Moon orbits the Earth, it appears
to change shape as it goes through
phases. The cause of the phases is one
of the greatest misconceptions in
astronomy. Many people feel Earth’s
shadow is responsible, but that is
Mars Global Surveyor (2003)
incorrect.
139 million km from Earth, 1 billion km from Jupiter
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sunlight
The Earth, Sun, and Time of Day
This diagram
explains
_________…
…but it’s a bit
complicated.
Let’s take it
_______ at a
time…
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The Sun is directly
overhead: it’s ____ here.
The Sun is on the
Western horizon: it’s
sunset (6:00 p.m.) here.
sunlight
Imagine you are
floating in space high
above the North Pole,
looking back down at
the _____. The Sun is
illuminating one side
of the Earth.
The Sun is directly beneath
your feet: it’s midnight here.
The Sun is on the
Eastern horizon: it’s
4
______ (6:00 a.m.) here.
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Astronomy 310 (Newbury)
May 15, 2007
The Orbiting Moon
Moon Phases
one side
dark
sunlight
one side lit
by sunlight
Moon
The Moon orbits
around the Earth
every ______days.
The Sun always
illuminates one
side of the Moon,
the side towards
the Sun, no matter
where the Moon is
in ________.
The big question is, what does the Moon look like
_____________ throughout the orbit
The key point is realizing we do not always see the
________ of the Moon. The amount of the sunlit half
we see depends on where the Moon is in it’s orbit.
see all dark,
sliver of lit
sunlight
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We see the new Moon during the day (but not ______).
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Waxing Crescent
Earthshine
see mostly dark
but some
lit, too
sunlight
Sometime there is so much light reflected back off the
______ and on the Moon that we can see the “_____”
portion of the Moon. We call this Earthshine.
One ______ of the way through the cycle (3 – 4 days)
we see a crescent Moon (in the evening). The
crescent “points” towards the Sun. The crescent is
______ every day, so it’s called the waxing crescent.
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Rychlik
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Astronomy 310 (Newbury)
May 15, 2007
First Quarter
Surface of the Moon
half
dark
half
lit
sunlight
One quarter of the way through the cycle (_____) we
see half the Moon lit (and half dark). We still call it
the first ______ Moon, though, because of its position
in the lunar cycle.
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The Moon has no atmosphere to scatter and bend the
sunlight, like we do here on Earth. So, when the Sun
sets or you’re in a shadow (on the Moon) it’s ______
______. And when the Sun is visible, it’s as bright as
the middle of the day.
The line between night and day on
the Moon is called the __________.
Using binoculars or a telescope, you
can clearly see the surface of the
Moon is not smooth, but that it’s
covered in craters. Around first
quarter is the _____ time for looking. Lammel
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Waxing Gibbous
Full Moon
but mostly lit
sunlight
Moon all lit
sunlight
some
dark
About 10 days into the lunar cycle, the ______ side of
the Moon is still growing. It’s called a waxing gibbous
(“________” means “humped” or “bulging”).
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can’t see any
of the dark side
________ through the cycle (2 weeks) the Moon is full.
You only see the full Moon from the night-side of Earth
(it rises in the East at sunset and sets in the West at
sunrise.)
Wait a minute! Won’t the Earth ______ the sunlight
No, not every lunar cycle. We’ll discuss lunar ______
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in the next section…
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Astronomy 310 (Newbury)
May 15, 2007
Waxing Gibbous
Third Quarter
sunlight
some
dark
one side
mostly lit
sunlight
one
half
dark
one
half lit
After the Full moon, the sunlit portion of the Moon
begins to get smaller (begins to “_______”). It’s still
gibbous, so we see the waning gibbous Moon early in
the _________.
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Three quarters of the way through the cycle, about 3
weeks, we see the ________ half the Moon lit and the
other half _______. This is the third quarter Moon.
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Waning Crescent
New Moon, Again
After 29.5 days, the ______ starts over again…
mostly dark
a bit
lit, too
sunlight
new Moon
very young
Moon
Near the end of the lunar cycle, we see only a
_______ (pointing towards the Sun). The crescent is
getting smaller each day, giving a waning crescent
Moon. We see it in the morning – just before ______
is best.
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very end
of cycle
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4

Astronomy 310 (Newbury)
May 15, 2007
sunlight
See how
easy it is
now _____!
Eclipses
There is a lot
of information
_____ inside
this diagram!
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APOD 2006 April 4
APOD 2006 April 4
Recall the Full Moon…
Eclipses
sunlight
Eclipses of the Sun and Moon are (the most)
spectacular astronomical events. Solar eclipses, as
we’ll see shortly, are difficult to see, so if you’ve ever
seen a total solar eclipse, you are _____________.
Recall that when the Moon on the side of the Earth
__________ the Sun, we see a full Moon.
An obvious question is, doesn’t the Earth ________
________ The answer is yes, sometimes, but not
every lunar cycle. Eclipses require special alignment.
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solar eclipse (August 1999)
APOD 2006 March 30
A solar eclipse occurs when
the Earth passes into the
________ of the Moon. The
Moon blocks the Sun, as
seen from Earth. It happens
only when the ______, Moon
and Earth are aligned.
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5

Astronomy 310 (Newbury)
May 15, 2007
Eclipses
Lunar Eclipses
A ______ eclipse occurs when
the Moon passes into the
Earth’s shadow. Earth ______
the sunlight that is supposed to
produce a full Moon. It
requires alignment of the Sun,
Earth and Moon.
Did you notice the ________
An eclipse is named after…
the object
being blocked
lunar eclipse (November 2003)
APOD 2003 November 21
the object doing
It seems like there should be a lunar eclipse ______
_______ when the Moon is full. This doesn’t happen,
though, because the Moon’s orbit is ____ about 5°
from the plane of the Solar System.
Because of the
tilt, sometimes the
Moon is above
the ecliptic and
sometimes it’s
below the ecliptic.
Eclipses are not
the blocking 21
________.
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Line of Nodes
Lunar Eclipse Y or N
Notice there are
two points on the
Moon’s orbit where
it _____________
the plane. These
points are on the
line of nodes.
In order for a lunar eclipse to occur, the ___________
must be on the line of nodes at exactly the same time
the Earth is in the right place in it’s orbit that the line of
nodes points towards __________:
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Astronomy 310 (Newbury)
May 15, 2007
Three Types of Lunar Eclipses
The Earth’s Shadow
It requires amazing alignment of the Sun, Earth and
Moon to produce a lunar eclipse. It doesn’t have to
be ______________, though, because the Sun, Earth
and Moon are not infinitely small points. They have
some size, so there is a some “leeway” for almost
perfect alignment.
This leeway means there are _______ lunar eclipses
each year. Depending on how ____ the alignment is,
three different kinds of lunar eclipses can occur…
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First, ________ the
shape of the Earth’s
shadow:
Pogge
(Ohio State)
The region behind Earth that receives __________ is
called the umbra (“umbra” means “shadow”, as in
“umbrella”). Because the Sun is so huge, there are
regions that get some sunlight, but not all of it. This is
the penumbra (the prefix “pen-” means “almost”, as in
__________, an “almost island”)
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If the full Moon
passes only
through the
penumbra, it is only
partially blocked.
Penumbra Lunar Eclipse
If the __________
passes through the
umbra, it is totally
blocked, producing
a ___ lunar eclipse
Total Lunar Eclipse
There may still be a significant amount of _________
hitting the Moon. Sometimes, you ______________ a
penumbral lunar eclipse is happening.
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Astronomy 310 (Newbury)
May 15, 2007
Why is the lunar eclipse red
The Moon may be directly behind the Earth, but it is
not completely dark because the Earth’s __________
bends the sunlight onto the Moon: refraction
Sure, but why is it ___ The Earth’s atmosphere also
scatters away shorter wavelength light (blue) leaving
the _____ wavelengths (red) to travel on to the Moon.
red and blue mixed
blue
red
Next Lunar Eclipse
The length of time the Moon spends eclipsed by the
Earth depends on its _____through the umbra. It can
last for up to 1:47 hours.
The next total lunar
eclipse is on August 28.
We should be able to
______ the whole event
from here in Vancouver.
This is a long-exposure picture that shows the
fainter, redder light during the eclipse.
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Espenak (Mr. Eclipse)
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If the full Moon
passes partly
through the umbra,
it is only ________
blocked.
Partial Lunar Eclipse
The portion of the Moon in the umbra may turn quite
dark (or red). The portion only in the penumbra may
still be _____, though, producing a partial lunar eclipse.
How Good is the Alignment, Anyway
Imagine making a scale model of a lunar eclipse.
The important quantities are:
Quantity
Length (km) Scale to Moon pinky fingernail
Moon diameter
3475 1
1 cm
Earth diameter
12 756 3.67 3.67 cm
Sun diameter 1 392 530 400.7 400 cm (____)
Earth-Moon distance 384 400 110.6 111 cm (1.1 m)
Earth-Sun distance 149 600 000 43 050 __________
(______ m)
1 392 530
= 400.7
3475
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Astronomy 310 (Newbury)
May 15, 2007
How Good is the Alignment, Anyway
Quantity
Scale to Moon head of a pin
Moon diameter
1
1 mm
Earth diameter 3.67 3.67 mm
Sun diameter 400.7 400 mm (40 cm)
Earth-Moon distance 110.6 111 mm (1.1 cm)
Earth-Sun distance 43 050 43 050 mm
(43 m)
model
Hold the head of the pin 1.1 cm from the head of the
quilt pin. Hold them so they line up with the Sun
circle across/down the hall!
Question
How good is the alignment, anyway
unbelievable!
I can’t believe it
ever happens!
no wonder lunar
eclipses are rare!
Geez, I couldn’t
even do it!
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Solar Eclipses
The Moon’s Shadow
Lunar eclipses occur when the Moon passes into the
shadow of the Earth. _____ eclipses occur when the
______ passes into the shadow of the Moon.
solar corona
prominences
(Espenak)
By remarkable chance,
the Moon is just the
right size and distance
from the Sun to almost
perfectly block out the
Sun’s disk, revealing
features normally
________ in the
brightness of the Sun.
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The shadow of the Moon also has a umbra and
penumbra region. The “tip” of the umbra just barely
________________ of
the Earth, “painting” a
dark circle on the
ground that races along
the __________at over
1700 km/h. A solar
eclipse never lasts
longer than 7½ minutes
at any location (and
usually it’s a lot less!)
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Astronomy 310 (Newbury)
May 15, 2007
Three Types of Solar Eclipse
Partial Solar Eclipse
If you’re at the right place on Earth at the right _____,
the shadow of the Moon will pass over you.
Sun moves across the sky
Moon crosses
in front of the Sun
totality
APOD 2006 April 4
Over several hours, you see a larger and larger piece
of the Sun “_______.” It gets darker and darker. During
a total solar eclipse, _______ (when the Sun is hidden)
last only a few minutes at your location.
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APOD 2002 June 12
If you are ___ on the
eclipse path, you
might only be in the
path of the Moon’s
__________. You’ll
see a partial solar
eclipse, instead.
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Annular Solar Eclipse
Next Solar Eclipse
The Earth–Moon ________
changes slightly. If a total
solar eclipse occurs when
the Moon is _____ from the
Earth, the disk of the Moon
might not cover the Sun,
producing an annular solar
eclipse (an “annulus” is a
“_____”)
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There is a solar eclipse
on Sep 11, 2007 (solar
and lunar eclipses almost
always happen during the
_______________, when
the line of nodes points
towards the Sun.)
It’s a partial solar eclipse
(the Moon’s umbra
almost misses Earth
entirely!) that we ______
see from BC.
eclipse
path
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