Moon Phases
& Eclipses
What patterns, motions, and events do we
notice in the sky?
What theories can we create to explain
them?
How can these theories be tested?
The last LUNAR eclipse
YOU might have seen…
September 28,
2015
The next LUNAR eclipse
YOU can see…
March 23,
2016
The next TOTAL SOLAR
eclipse YOU can see…
Monday
morning,
21 August
2017
The next “nearby” TOTAL
SOLAR eclipse YOU can see…
August
21 2017
Observations of the Moon
 Sequence of phases
every “moonth”
 We always see the
same “face”
Observations of the Moon
 Occasionally turns dark
gray & even red!
 Can seem bigger next to
the horizon!
 Phases repeat ~30 days
 A “moonth” of time
 Tied to religious calendars
around the globe
 Ramadan
 Chinese New Year
 Easter
 Rosh Hashanah
 Gudi Padwa & Vasant
Panchami
Observations of the Moon
Sequence of repeated
phases over ~ “moonth”
Sunlight reflecting off
Moon that is visible to us
NOT Earth’s shadow!!
Observations of the Moon
IS the phase the same on the same day
around the world?
Do people in London see the same phase as
we do in Hayward?
Observations of the Moon
IS the phase the same on the same day
around the world?
Most people would say…… NO!
They are wrong!
Compare times
For Earth to rotate: hours
For the Moon to move & change phase: days
Observations of the Moon
Do people in both hemispheres see the
same view?
Does an observer at Chabot see the same
thing as someone in Santiago, Chile?
Most people would say…… er…YES?
They are wrong!
 Phases are “reversed” in
Southern Hemisphere!
 Same side of moon is still
lit by the sun
 Observation from “down
under” reverses view.
 Northern
Hemisphere
Phases!
 Southern
Hemisphere
Phases!
Seeing the moon from different
places on Earth!
Seeing the moon from different
places on Earth!
Northern Hemisphere
Southern Hemisphere
The Moon Illusion!
The Moon Illusion!
What theories can we develop?
WHY does the moon seem larger?
Because it IS larger?
Because it is an illusion
We see horizon different than zenith?
We don’t have a “reference” for Moon when it’s
higher in the sky?
How can you TEST these hypotheses?
The Moon Illusion!
The Moon DOES vary in distance….
The Moon Illusion!
….but not over a few hours!
The Moon Illusion!
Perhaps… we don’t see the sky as symmetric – the horizon is
farther away than the sky above us?
Solar Eclipses
 Occur at NEW moon phase
 While partial, a “bite” out of the Sun
 Last 1+ hours
 IF total…
 Sky goes dark for a few minutes
 See planets and stars near the sun
 See Sun’s corona and chromosphere
Shadow of
the moon
covers small
oval on Earth
Corona
Chromosphere
Annual Solar Eclipse
Time-lapse series
of photos
-What time of day?
-How long did this
take?
Hint: Northern
Hemisphere!
Lunar Eclipses
 Occur at FULL moon phase
 The Moon looks full, but dim
 The Earth’s curved shadow falls across the
moon
 Last 2+ hours
 IF total…
 Moon can look red for an hour
At the start of a lunar eclipse, you can see
the Earth’s Shape through its shadow…
Lunar Eclipse Time-Lapse
Note the curved shadow of the
Earth across the moon.
Predicting Eclipses
Eclipse “seasons”
About twice a year
Always at least (2) eclipses
One of each (lunar + solar)
About 2 weeks apart
Pattern repeats about 18 years for location
and type
Eclipse “Seasons”
The next LUNAR eclipse
YOU can see…
Sunday night,
27 September
2015
Sunday night,
27 September 2015
• Moon rises with partial eclipse
already started
• Total beings 7:11 PM
• Max Eclipse 7:47
• Total Ends 8:23
• Partial Ends 9:27
• Then… just a full moon!
A really “nearby” TOTAL SOLAR
eclipse YOU might see…
August
12 2045
Chabot College