Transcript Moon Phases and Eclipses - Academic Computer Center

Phases of the Moon
• The Phases of the Moon
are the variations in the
Moon’s appearance as the
Moon orbits the Earth.
• They are due to the
changing Sun-Earth-Moon
angle through each month.
• The following is the cycle
of lunar phases: new,
crescent, first quarter,
gibbous, full, gibbous,
third quarter, crescent, new
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Moon Phases
• The Moon orbits
the Earth in about
one month (29.5
days)
• Over one orbit the
appearance and
rise and set times
change with the
cycle of Lunar
Phases.
• The figure is not
to scale
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Light & Dark
How the Earth and Moon would
look high above Earth’s North Pole.
The figure is not to scale.
• We only see the Moon because
sunlight reflects off its surface.
• At any one time, half the Moon
is always lit and half is in
darkness.
• The amount of the illuminated
half we see from Earth depends
on the position of the Moon in
its orbit
• The time of day the Moon is
visible also depends on its
phase.
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Example: Observing the Moon
• Between January 23-25, 2004,
at dusk, the Moon was visible
in its waxing crescent phase.
• The first night it appeared
close to the Sun. Subsequent
nights it appeared higher in the
sky (farther from the Sun) and
the lit portion appeared to be
growing larger.
• What do you think you would
see the next night? How about
a week later?
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Lunar Phase Terms
• The cycle of Lunar Phases
starts at the New Moon.
• At New Moon the Moon is
not visible to us on Earth.
• From New Moon to Full
Moon the illuminated
fraction of the Moon we
see from Earth grows. It is
said to be waxing.
• After Full Moon the
fraction
of
the
illuminated
We can only see the half of the
Moon above and to the right of the Moon visible from Earth
diagonal line drawn on the Moon shrinks. It is said to be
waning.
in the figure above.
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The Cycle of Lunar Phases
• The Lunar cycle is
split into quarters
–
–
–
–
New Moon
1st Quarter
Full Moon
3rd (or Last) Quarter
• Since the whole cycle
lasts about a month
each quarter lasts
about a week.
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As you view
the moon from
different
directions
(relative to the
Sun) its
appearance
changes.
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crosses meridian
at sundown
crosses meridian
at about 9:00 pm
crosses meridian
at about 3:00 pm
sunlight
crosses
meridian
at midnight
crosses
meridian
at noon
sunlight
crosses meridian
at about 9:00 am
crosses
meridian
at about 3:00 am
crosses meridian
at dawn
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The Lunar Phases Web Tool
• This is an interactive
tool that helps illustrate
how
– the time of day,
– the phase of the Moon
and,
– the position of the
Moon in its orbit are all
related to one another.
• The time that is used in
this tool is only an
average 6 PM
represents sunset, 6
“Lunar Phases Web Tool” located at
AM represents sunrise,
http://www.calvin.edu/~lmolnar/moon/index.html
etc.
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