Night Sky III Planetary Motion Lunar Phases · Astronomy 1 - Elementary Astronomy LA Mission...

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

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

Last Class

• Annual Motion

• Zodiac

• Seasons

• Planetary Motion

This Class

• Seasons Questions revisited

• Planetary Motion

• Lunar Phases

• LT: Predicting Lunar Phases

• Eclipses (time permitting)

Spring F2015

Seasons Review

• Axial Tilt

• Energy transfer

Let’s Practice

Which lettered position (A-E), in the image below, best represents the location on Earth that is experiencing summer in the Southern Hemisphere?

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

Spring F2015

Planets... the Wanderers

Planets... the wanderers

• It was a warm summer evening in ancient Greece....

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

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?

The Motion of the Planets

• orbit in almost the same plane

• relative positions change with time

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!

Retrograde Motion

• http://www.bisque.com/help/Patterns/image/retrograde_motion_of_mars_wmf.gif

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

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

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

Never, Ever, Never, Ever, EVER!!!!!!!

Spring F2015

Lunar Cycles & Phases

PHASES OF THE MOON

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

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

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

Lunar Phase Diagram

• Waxing — getting bigger (approaching Full)

• Waning — getting smaller (approaching New)

Let’s Practice

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?

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?

Which of these positions would be the waning crescent moon?

Is there really a “dark side of the Moon” that never receives sunlight?

A. yes

TIMING OF LUNAR PHASES

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?

Lunar Phase Timing

• Sun overhead — noon

• new moon is transiting

• 3rd Quarter is setting

• 1st Quarter is rising

Lunar Phase Timing

• Sun is setting — 6 PM

• 1st Quarter is transiting

• New Moon is setting

• Full moon is rising

Spring F2015

LT Predicting Moon Phases (If time)

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

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

At what local apparent solar time does the full moon transit?

A. noon

B. 6 PM

C. 9 PM

D. midnight

At midnight, local apparent solar time, what phase will be rising?

A. Waning Gibbous

B. First Quarter

C. Third Quarter

D. New

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

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

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

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

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?

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.

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

Lunar Eclipse

Path for penumbral eclipse

Lunar Eclipse

Progression of Total Lunar Eclipse

<----------

Partial Lunar Eclipse ---------->

Lunar Eclipses 2010-2017

Solar Eclipses

Image: Sanhujinka.com

Solar Eclipse

A Total Solar Eclipse

Solar Eclipses

• Next good US TOTAL solar eclipse opportunity is in 2017

Let’s Practice

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

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

Topic for Next Class

• History part I

• Greeks to Kepler

• Kepler & Brahe

• Kepler’s Laws

Reading Assignment

• Ch 3 in either text

Homework

• Sci, Annual, Diurnal due 9/22

Night Sky III Planetary Motion Lunar Phases · Astronomy 1 - Elementary Astronomy LA Mission...

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