Announcements:

•Assignment for Monday: read chapter 4 of text

•No quiz on Monday. However, we will start class with two very simple questions from Chapter 4. Anyone who read the chapter should be able to answer these questions.

• Look for news on Thursday about Kepler - homework extra credit if you write a one paragraph summary of what you learned

Cycles of the Moon

Chapter 3

New Moon

Waxing Crescent

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1st Quarter

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Waxing Gibbous

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Full Moon

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Waning Gibbous

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3rd/Last Quarter

Waning Crescent

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All Together

The diagram below shows Earth and the Sun as well as five different positions for

the Moon. Which position of the Moon best corresponds with the phase of the Moon

shown in the figure to the right? QuickTime™ and a

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1

2

3

4

5

Not to Scale

Earth Sun

If the moon reaches full phase on May 6, it is at _____ phase on May 17.

1. new

2. waxing crescent

3. waxing gibbous

4. waning gibbous

5. waning crescent

Review: Phases of the Moon

The third quarter phase moon rises at about:

1. sunrise.

2. noon.

3. sunset.

4. midnight.

5. There is no way to predict the time that a particular phase rises.

Review: Phases of the Moon

The Moon’s Orbit

The Earth exerts tidal forces on the moon’s rocky interior.

→ It is rotating with the same period around its axis as it is orbiting Earth (tidally locked).

→ We always see the same side of the moon facing Earth.

An astronaut on the Moon would see the Sun rising

a. every 24 hoursb. every weekc. every monthd. never

An astronaut on the Moon would see the Earth rising

a. every 24 hoursb. every weekc. every monthd. never

Moon’s Orbit: 12% variation over one

lap!

Perigee: closest to Earth

Apogee: farthest from Earth

The Moon’s Orbit

Moon’s orbit about Earth is not perfectly circular. The consequence is that the Moon gets slightly larger and smaller in the sky. The change is only about 12%!

Inclination of Moon’s Orbit

Inclination of orbital plane relative to the ecliptic is 5.14 degrees. = ~10 moon diameters

Lunar Eclipses

Earth casts its shadow out into space as it orbits the Sun. The Moon is eclipsed when it passes in the Earth’s shadow. Earth’s shadow is larger than Moon.

Lunar Eclipses

A total lunar eclipse can last

up to 1 hour and 40 min.

During a total eclipse, the moon has a

faint, red glow, reflecting sun light scattered

in Earth’s atmosphere.

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Total Lunar Eclipse of 2/20/08

•Visible across the Americas, Europe and Africa

•Totality lasts nearly an hour

•Distinctive “red glow”

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1. Feb 21, 2008 and June 15, 2011

2. Dec. 21, 2010 and December 10, 2011

3. Dec 10, 2011 and Oct. 8, 2014

4. Feb. 21, 2008 and June 15, 2011

5. Dec 10, 2011 and Oct. 8, 2014

Of the six total lunar eclipses listed in this table, which two definitely cannot be observed by someone under clear skies located in Greenwich, England?

Solar Eclipses

Moon’s shadow is small. Sun is eclipsed for observers within the Moon’s shadow.

Typical speed: 1000 MPHSize of Shadow: 100 miles

Solar Eclipse Geometry

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So….. What phase of the Moon must it be to have a solar eclipse?

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Observing a Solar Eclipse

Observing a Solar Eclipse

Total Solar EclipseMarch 29, 2006, Side, Turkey

Observing a Solar Eclipse

Annular EclipseMay 30, 1984

Observing a Solar Eclipse

March 29, 2006Adrasan, TurkeyDigital MosaicTotality: about 4 minutes

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2006 Total Solar Eclipse

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360 Sunset During the Eclipse

Solar Eclipse Seen from Space

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…. And another

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How Often Do They Occur

•Moon’s orbit “precesses” (wobbles) so that the node moves Eastward about 20 degrees per year

•Sun crosses node about every 173 days

•When Sun is near the node, it is “eclipse season” and solar and lunar eclipse occur two weeks apart

•About two node crossings per year

Ecliptic and Moon’s Orbit Offset by 5

35 days for possible overlap. (It takes the Sun 35 days to travel this far

across the sky Only about 3 days for Moon to cover the same angle.)

It is much more probable that you will see a Lunar eclipse only because significantly more people on Earth can see it at the same time.

Lunar eclipses are not more frequent than solar eclipses.

Frequency of Lunar vs. Solar Eclipses

We can see total solar eclipses because:

1. the linear diameters of the sun and the moon are almost equal.

2. the distances to the sun and the moon are about the same.

3. the angular diameters of the sun and the moon are almost equal.

4. total solar eclipses would be visible on any planet with a moon.

5. the moon always shows the same face to the Earth.

Observing a Solar Eclipse

A total lunar eclipse lasts much longer than a total solar eclipse. Why?