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Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Night Sky III Planetary Motion
Lunar Phases
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Quotes & Cartoon of the Day
“Everything has a natural explanation. The moon is not a god, but a great rock, and the sun a hot rock. “
-- Anaxagoras (500 BC – 428 BC)
“Nature gives to every time and season some beauties of its own; and from morning to night, as from the cradle to the grave, it is but a succession of changes so gentle and easy that we can scarcely mark their progress.“
-- Charles Dickens
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Announcements
• First HW, through part of today’s material, posted
• due Tuesday 9/22
• First midterm currently planned 9/24
• may move out one week
• will confirm Tuesday
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Last Class
• Annual Motion
• Zodiac
• Seasons
• Planetary Motion
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
This Class
• Seasons Questions revisited
• Planetary Motion
• Lunar Phases
• LT: Predicting Lunar Phases
• Eclipses (time permitting)
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Seasons Review
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Seasons Review
• Axial Tilt
• Energy transfer
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Which lettered position (A-E), in the image below, best represents the location on Earth that is experiencing summer in the Southern Hemisphere?
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
If Earth were tilted more (60° rather than 23.5°), then during winter at your location you would _____ compared to what you experience during winter now.
A. experience cooler temperatures
B. experience warmer temperatures
C. not experience any significant change in temperature
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Planets... the Wanderers
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Planets... the wanderers
• It was a warm summer evening in ancient Greece....
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Apparent Motion of Planets
• Indeed originally named for their “wandering” movement
• “Late Old English planete, from Old French planete (Modern French planète), from Late Latin planeta, from Greek planetes, from (asteres) planetai "wandering (stars),..."
• Most of the time rise a bit later each night
• move eastward against the background stars
• Sometimes appear to go “backwards” for a while
• i.e. rise earlier each night/go westward
• This is called apparent retrograde motion
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Mars and Retrograde Motion
QuickTime movie from Dr. Ted Snow's web site at The University of Colorado, Boulder.)
WHY DO WE SEE APPARENT RETROGRADE MOTION?
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Motion of the Planets
• orbit in almost the same plane
• relative positions change with time
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Apparent Retrograde Motion
• Planets orbit the Sun at differing rates.
• sometimes Earth will “catch up to and pass” another planet
• planet appears to pause in its eastward progression and “move backwards”
• never actually change orbit!
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Retrograde Motion
• http://www.bisque.com/help/Patterns/image/retrograde_motion_of_mars_wmf.gif
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Frequency and Length Vary
• Synodic period — how often
• Example Mars
• 3/1/2014 to 5/19 2014
• 4/17/2016 to 6/29/2016
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
For how many days was this planet in retrograde motion?
A. 10 days
B. 12 days
C. 15 days
D. 17 days
E. 32 days
May
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
On which date would the planet appear to rise in the west?
A. March 1
B. March 31
C. April 5
D. April 12
E. Never
May
Never, Ever, Never, Ever, EVER!!!!!!!
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Lunar Cycles & Phases
PHASES OF THE MOON
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Moon’s Orbit
• The Moon orbits the Earth every 27.3 days (sidereal month)
• sidereal means relative to the stars
• Full moon to full moon is every 29.5 days (synodic month)
• This is a right-handed revolution, like the Earth
• The Moon is tidally locked to the Earth
• It also rotates once every 27.3 days
• Same side always faces Earth
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Lunar Phases
• We see different phases of the Moon depending on where the Moon is in it’s orbit around the Earth, with respect to the Sun.
• Half the Moon is lit at all times by the Sun.
• We view the half dark/half lit Moon from different angles, which creates the different appearances at different phases
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Moon Phase Animation
• We see different phases of the Moon depending on where the Moon is in it’s orbit around the Earth, with respect to the Sun.
• Half the Moon is lit at all times by the Sun.
• We view the half dark/half lit Moon from different angles, which creates the different appearances at different phases
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Lunar Phase Diagram
• Waxing — getting bigger (approaching Full)
• Waning — getting smaller (approaching New)
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The diagram below shows Earth and the Sun as well as five different possible positions for the Moon. Which position (B-D) of the Moon best corresponds with the Moon phase shown in the upper right corner?
XX
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The diagram below shows Earth and the Sun as well as five different possible positions for the Moon. Which position (A-E) of the Moon best corresponds with the Moon phase shown in the upper right corner?
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Which of these positions would be the waning crescent moon?
A. 2
B. 4
C. 6
D. 8
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Is there really a “dark side of the Moon” that never receives sunlight?
A. yes
B. no
TIMING OF LUNAR PHASES
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Lunar Phases & Timing
• Different phases rise, set & transit @ different times of day
• transit — reaches the highest point/between rising & setting
• How do we tell what time it is?
• Or, how did we before watches, iPhones & atomic clocks?
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Lunar Phase Timing
• Sun overhead — noon
• new moon is transiting
• 3rd Quarter is setting
• 1st Quarter is rising
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Lunar Phase Timing
• Sun is setting — 6 PM
• 1st Quarter is transiting
• New Moon is setting
• Full moon is rising
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
LT Predicting Moon Phases (If time)
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Which phase of the Moon rises at 9 AM?
A. waning gibbous
B. third quarter
C. first quarter
D. waxing crescent
E. none of the above
LT PREDICTING MOON PHASES
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Which phase of the Moon rises at 9 AM?
A. waning gibbous
B. third quarter
C. first quarter
D. waxing crescent
E. none of the above
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
At what local apparent solar time does the full moon transit?
A. noon
B. 6 PM
C. 9 PM
D. midnight
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
At midnight, local apparent solar time, what phase will be rising?
A. Waning Gibbous
B. First Quarter
C. Third Quarter
D. New
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
If you see a crescent moon very high in the sky in the fairly early morning morning, is it waxing or waning?
A. waxing
B. waning
C. it depends on the day of the month
D. this is not possible
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
You observe a full moon rising around 7 P.M. In what phase will you observe the moon setting the next morning?
A. New Moon
B. Waning Gibbous
C. Full Moon
D. Third Quarter
ECLIPSES
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Eclipses
• Lunar eclipse — Earth precisely between Moon and Sun
• Earth’s shadow falls on Moon
• Moon goes dark (reddish actually)
• Solar eclipse — Moon precisely between Sun and Earth
• Moon’s shadow falls on Earth
• Sunlight blocked completely in some places (total solar eclipse)
• partly in some places (partial solar eclipse)
• and not at all in most places
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Apparent Size of Sun and Moon
• The Sun and Moon appear to have the same size when viewed from Earth.
• Makes total solar eclipse possible
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Eclipses
• So... once a month the Moon is between the Earth and the Sun....
• New Moon…
• Why don’t we have a solar eclipse every month?
• Or a lunar eclipse every month?
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Moon’s Orbit is tilted
• The Moon’s orbit tilted relative to the Earth’s orbit around the sun by about 5°
• (recall its apparent angular size is ~ 0.5°)
• Most of the time, the moon is above or below the direct line from Sun to Earth.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Moon’s Orbit is tilted
• Periodically, the Moon crosses the line from Earth to Sun.
• If it does so at full moon, we have a Lunar Eclipse
• The Earth’s shadow falls on the Moon
• If it does so at new moon, we have a Solar Eclipse
• The Moon’s shadow Falls on the earth
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Lunar Eclipse
Path for penumbral eclipse
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Lunar Eclipse
Progression of Total Lunar Eclipse
<----------
Partial Lunar Eclipse ---------->
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Lunar Eclipses 2010-2017
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Solar Eclipses
Image: Sanhujinka.com
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Solar Eclipse
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
A Total Solar Eclipse
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Solar Eclipses
• Next good US TOTAL solar eclipse opportunity is in 2017
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Suppose it is early in the month and you are going on a cruise to view a total solar eclipse later the same month. The moon is currently full. If it only takes a day or so to get to the viewing location, about when might your cruise depart?
A. tomorrow
B. next week
C. about two weeks from today
D. at the very end of the month
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
If you found yourself on a planet very similar to Earth with a moon very similar to our Moon, what would you conclude if you observed a total lunar eclipse every full moon?
A. That this planet’s moon orbits in the same plane as the planet orbits its star.
B. That this planet’s moon is much larger than our Moon.
C. That this planet’s star is much more distant than our Sun.
D. That this planet’s moon orbits over the poles of the planet rather than near its equator.
WRAP-UP
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Topic for Next Class
• History part I
• Greeks to Kepler
• Kepler & Brahe
• Kepler’s Laws
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Reading Assignment
• Ch 3 in either text
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Homework
• Sci, Annual, Diurnal due 9/22