Assign. #1 distributed Friday Sep. 15.Due in your lab section slot, by 5 PM Sep 23.

Office hours Mon, Thurs, and Friday this week. See Web page.

Lab 1 will be due between Sep. 25 - 28.

The motion of The motion of

the Moonthe MoonANNOUNCEMENTS

The Moon, Our Constant CompanionThe Moon, Our Constant Companion

Why do we see phases of the Moon?

What conditions are necessary for an eclipse?

Why were eclipses difficult for ancient peoples to

predict ?

Our goals for learning:

Note: the Chpt. 2 Moon tutorial on

masteringastronomy.com is useful!

AnimationsAnimations

Ecliptic Plane

Orbit of Moon

Why do we see the same face?Why do we see the same face?

Rotation period = orbital period

What do you see if you're standing on the

Moon looking at Earth?

AnimationsAnimations

Causes of lunar phases

Lunar MotionLunar Motion

Phases of the Moon’s 29.5 day cycle

(is that synodic or sidereal???)new

Crescent

first quarter

gibbous

full

gibbous

last quarter

crescent

Waxing

Waning

The lunar phasesThe lunar phasesNotice that the size seems

to change. Why?

Notice that it 'wobbles' a

bit. Why?

The lunar phasesThe lunar phasesNotice that the size seems

to change. Why?

Moon is not at a constant

distance.

Notice that it 'wobbles' a

bit. Why?

Because the orbital speed

is not exactly constant

Called 'librations'

Why do we see phases?Why do we see phases?

Half the Moon

illuminated by Sun

and half dark

We see some

combination of the

bright and dark

faces

Preliminaries: Local Solar timePreliminaries: Local Solar time

Interactive

applet at

mastering

astronomy

.com

Phases of the Moon. An example: Phases of the Moon. An example:

the waxing crescentthe waxing crescent

From the

publisher's

web site.

Rising/setting times of the MoonRising/setting times of the Moon

Depending on the phase

of the Moon it always

rises and sets at the

same (rough) local solar

time.

This is due to simple

geometry of the

illumination by the Sun.

See Fig 2.21 of Cosmic

Perspective.

NOTE: The times above neglect the Earth's tilt!

AnimationsAnimations

Phases of the Moon

Rise/set time vs phase

Handout given in class

Q: You see a quarter moon Q: You see a quarter moon

rising after drinking in the Pit. rising after drinking in the Pit.

What time is it?What time is it?

A) 9 PM

B) Midnight

C) 3 AM

D) 6 AMBonus : First or Third quarter?Bonus : First or Third quarter?

Eclipses : Puzzles for ancient Eclipses : Puzzles for ancient

astronomers/astrologersastronomers/astrologers

The Earth & Moon cast

shadows.

When either passes

through the other’s

shadow, we have an

eclipse.

Why don’t we have an

eclipse every full & new

Moon?Eclipses

twice a

month?

The Moon's orbit is inclined.The Moon's orbit is inclined.Moon not necessarily in the ecliptic when it

comes `into line' with the Sun

AnimationsAnimations

Moon's orbit tilt

Eclipse Seasons...

How rare are eclipses

Eclipse PredictionsEclipse PredictionsEclipses recur in the approx. 18 yr, 11 1/3 day

saros cycle

But even then, eclipse location and type (e.g.,

partial, total) may vary. Why?

Lunar Eclipses Lunar Eclipses (way out of scale)(way out of scale)

From the

publisher's

web site.

Lunar Eclipse SequenceLunar Eclipse Sequence

Is time

going

L to R

or

R to L

?????

Lunar eclipse geometryLunar eclipse geometry

Solar eclipse geometries

Total

Partial

Annular

Does time go from right to left or left to right here?

Time-lapse photo taken in northern Europe

Solar EclipsesSolar Eclipses

Animation