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

Chapter 3 Cycles of the Moon

New Moon

Waxing Crescent

1st Quarter

Waxing Gibbous

Full Moon

Waning Gibbous

3rd/Last Quarter

Waning Crescent

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? 1 5 Earth Sun 2 4 3 Not to Scale

Review: Phases of the Moon If the moon reaches full phase on May 6, it is at _____ phase on May 17. new waxing crescent waxing gibbous waning gibbous waning crescent

The third quarter phase moon rises at about: Review: Phases of the Moon The third quarter phase moon rises at about: sunrise. noon. sunset. midnight. There is no way to predict the time that a particular phase rises.

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 hours b. every week c. every month d. never An astronaut on the Moon would see the Earth rising a. every 24 hours b. every week c. every month d. never

Moon’s Orbit: 12% variation over one lap! VERY EXAGGERATED Apogee: farthest from Earth Perigee: closest to 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.

A total lunar eclipse can last up to 1 hour and 40 min. 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.

Total Lunar Eclipse of 2/20/08 Visible across the Americas, Europe and Africa Totality lasts nearly an hour Distinctive “red glow”

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? Feb 21, 2008 and June 15, 2011 Dec. 21, 2010 and December 10, 2011 Dec 10, 2011 and Oct. 8, 2014 Feb. 21, 2008 and June 15, 2011

Solar Eclipses Moon’s shadow is small. Sun is eclipsed for observers within the Moon’s shadow. Typical speed: 1000 MPH Size of Shadow: 100 miles

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

Observing a Solar Eclipse

Observing a Solar Eclipse Total Solar Eclipse March 29, 2006, Side, Turkey

Observing a Solar Eclipse Annular Eclipse May 30, 1984

Observing a Solar Eclipse March 29, 2006 Adrasan, Turkey Digital Mosaic Totality: about 4 minutes

2006 Total Solar Eclipse

360 Sunset During the Eclipse

Solar Eclipse Seen from Space

…. And another

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.)

Frequency of Lunar vs. Solar Eclipses 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.

We can see total solar eclipses because: the linear diameters of the sun and the moon are almost equal. the distances to the sun and the moon are about the same. the angular diameters of the sun and the moon are almost equal. total solar eclipses would be visible on any planet with a moon. 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?