Chapter 3 Section 1

The Phases of the Moon

The Motion of the Moon2 things about motion of the moon:

We see it moving eastward against the background of stars

It moves about 13˚ eastward in the sky each nightWe notice that the markings on its face don’t

change

Moon orbits around Earth at an average distance of 384,400 km (30 times Earth’s diameter)Its orbit is slightly elliptical, so its distance

from Earth can vary up to 6%

The Motion of the MoonSidereal Period is the period of rotation

or revolution of an astronomical body referred to the starsIt takes the Moon 27.321661days for the moon to

circle the sky once and return to the same place among the stars

We see the same side of the moon because it rotates on its axis to keep one side facing EarthIf it didn’t rotate, then we would see a different

sides of the moon in different parts of its orbit

The Phase CycleAs the moon moves around the sky, the

sun illuminates different amounts of the side of the moon facing Earth, and so the moon passes through a sequence of phasesWhen we see no moon in the sky on a clear night it is

called a new moon, which is the start of the lunar phases

As we continue to watch the progression the light we see reflected waxes (grows) until it is fully illuminated, which is called a full moon

The 2nd half of the lunar cycle reverses the first half because the reflected light of the moon wanes (shrinks)

The Phase CycleSynodic Period – period of rotation

or revolution of a celestial body with respect to the sunCycle of lunar phases takes 29.53 days (little

over 4 weeks)Each phase takes about a week to complete

http://ed-tech-integration.pbworks.com/w/page/8270144/Moon%20Phase%20Images

3rd quarter orLast Quarter

Starting at New Moon the phases move around the diagram in a counter-clockwise direction.

Similar to Figure 3-3 in your book

Chapter 3 Section 2

The Tides

The Causes of the TidesTides are produced by a difference between

the gravitational force acting on different parts of an object

The side of the Earth facing the moon is about 4000 miles closer to the moon that is Earth’s centerMoon’s gravity pulls more strongly on the oceans

on the near side than on Earth’s centerThis difference is small, only about 3% of the

moon’s total gravitational force on Earth, but it is enough to make the ocean waters flow into a bulge on the side of Earth facing the moon

The Causes of the TidesA bulge also forms on the side of

Earth facing away from the moonEarth’s far side is about 4000 miles

farther from the moon than Earth’s center, and the moon’s gravity pulls on it less strongly than it does on Earth’s centerThis causes a small force that makes the

ocean waters on Earth’s far side flow away from the moon

http://geography.about.com/od/physicalgeography/a/tides.htm

The Causes of the TidesEven though Earth rotates on its axis, the

tidal bulge remains fixed along the Earth-moon line

As Earth turns and carries us into the tidal bulge, the ocean water deepens, and the tide crawls up the beach

Since there are two bulges on opposites sides of Earth, the tides rise and fall twice a day, and the times of high tide and low tide depend on the phase of the moon

http://en.wikipedia.org/wiki/File:Bay_of_Fundy_Low_Tide.jpg

Both of these picture were taken in a harbor on the Bay of Fundy. The picture on the right was taken at high tide and picture on right was taken at low tide. The Bay of Fundy has the largest tidal range (over 12 meters) in the world.

The Causes of the TidesAt new moon and full moon, the moon and

sun produce tidal bulges that join together to cause extreme tidal changes

Spring tides – occur at new moon and full moon phases High tide is very high

Neap tides – occur at 1st quarter and 3rd quarter moon phasesLow tide is very low

http://home.hiwaay.net/~krcool/Astro/moon/moontides/

Tidal EffectsTidal forces can have surprising effects

on both rotation and orbital motionsFriction of Earth’s ocean waters against the

seabeds slows Earth’s rotation – days a getting 0.001 second longer per century

Tides are slowing Earth’s rotation by about 0.002 second per day – adds almost a second longer per year

Earth’s gravitational force has slowed the moon’s rotation

Moon’s orbit is growing about 3.8 cm per year, so it is getting further away from us

Chapter 3 Section 3

Lunar Eclipses

Earth’s ShadowA lunar eclipse occurs at full moon when

the moon moves through Earth’s shadowEarth’s shadow consists of 2 parts:

Umbra – region of total shadowPenumbra – region where sunlight is

dimmed, but not totally extinguished

This diagram was copied from Nick Strobel's Astronomy Notes. Go to his site at www.astronomynotes.com for the updated and corrected version.

Total Lunar EclipsesA lunar eclipse occurs when the moon

passes through Earth’s shadow and grows dark

If the moon passes through the umbra and no part of the moon remains outside the umbra in the partial sunlight of the penumbra, the eclipse is called a total lunar eclipse

Total Lunar Eclipse Progression

Total Lunar EclipsesEven when the moon is totally eclipsed, it

doesn’t disappear completelyThe bending of sunlight by our atmosphere

leaks into the umbra and bathes the moon in a faint glow

Since blue light from the sun is scattered by Earth’s atmosphere more easily than red light, it is the red light that penetrates to illuminate the moon in a coopery glow

http://www.skyandtelescope.com/eclipses/m970916a.html

Partial and Penumbral Lunar EclipsesNot all eclipses are totalIf the moon’s orbit carries the full moon too far north or

south of the umbra, the moon may only partially enter the umbraThis results in a partial lunar eclipse

Only part of the moon remains outside the umbra, it receives some sunlight and looks brighter in contrast with the dark part of the moon inside the umbra

If the orbit of the moon carries the moon far enough north or south of the umbra, the moon may only pass through the penumbra and never reach the umbraThis results in a penumbral eclipse

Moon is in the partial shadow of the penumbra which causes the moon to only partially dim

Most people glancing at this type of eclipse won’t notice any difference from a full moon

Chapter 3 Section 4

Solar Eclipses

Solar Eclipses

A solar eclipse occurs when the moon moves between Earth and the sunTotal Solar Eclipse – takes place when

the moon covers the disk of the sun completely

Partial Solar Eclipse – takes place when the moon covers only part of the sun

http://www.mreclipse.com/SEphoto/SEgallery1/SEgallery1.html

The Moon’s ShadowThe moon’s total (umbral) shadow

produces a spot of darkness roughly 167 miles in diameter on Earth’s surface

If we are in this spot of total shadow, we will see a total Solar Eclipse

If we are just outside the total shadow but in the penumbra, we see part of the sun peeking around the moon, and the eclipse is partial

If we are outside of the penumbra, we will see no shadow at all

Found on google images

Total Solar Eclipses

A total solar eclipse begins when we first see the edge of the moon encroaching on the sun. This is the moment when the edge of the

penumbra sweeps over our locationDuring this partial phase, part of the

sun remains visible, and it is hazardous to look at the eclipse without protectionDangerous invisible heat radiation

(infrared) can burn the retina of our eyesBest to observe the partial phases with a

pinhole projectionNext total solar eclipse visible from the

United States will occur August 21, 2017