Lunar Phases

and Eclipses

http://solarsystem.nasa.gov/multimedia/gallery/Earth_Moon.jpg

Created by the Lunar and Planetary InstituteFor Educational Use Only

LPI is not responsible for the ways in which this powerpoint may be used or altered.

Preliminary TopicsBefore students can understand the

reason for phases, they need to understand:

• The Moon orbits the Earth

• The Moon orbit at an angle with respect to the Earth’s orbit around the Sun

• The Moon doesn’t shine on its own; it reflects sunlight

• The scale of the Moon and Earth’s sizes and distance

Please go through Earth and Moon statistics before trying to cover the reason for phases or eclipses.

Ecliptic planeMoon’s orbital plane

The Moon

• The Moon shines by reflected sunlight.

– On average, it reflects about 7% of the incident

sunlight.

– The Moon appears about 400,000 times fainter

than the Sun in the sky.

• The phases of the Moon are the result of

varying viewing angles throughout the

month.

– A common misconception is that the phases of the

Moon are caused by the shadow of the Earth.

Moon Size

~ 1/4 width of Earth

Radius of 1080 miles

Gravity ~1/6 of Earth’s

http://grin.hq.nasa.gov/IMAGES/SMALL/GPN-2000-001444.jpg

http://visibleearth.nasa.gov/view_rec.php?id=1624

Earth and Moon to Scale

If Earth were a basketball, then the Moon would be a

tennis ball,

23.5 feet away

Moon Rotation Spins on axis (rotates) once every 27.3 days

Tilted ~1.5 degrees

(Earth = 23.5)

Moon’s Orbit Orbits (revolves around) Earth every 27.3 days

Elliptical orbit (not a perfect circle)

360,000 km 406,000 km 224,000 miles 252,000 miles http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=442

Moon Stats Moon’s orbit around Earth is inclined about 5 degrees to Earth’s plane of orbit around the Sun

Ecliptic plane

Sun EarthMoon

Moon’s orbital plane

Image created by LPI staff

New (couple days)

Waxing Crescent (several days)

1st Quarter

Waxing Gibbous (several days)

Full

Waning Gibbous (several days)

3rd Quarter

Waning Crescent (several days)

New

Phases: Observing and Identifying

http://www.lpi.usra.edu/education/skytellers/moon_phases/about.shtml

Phases--Causes

• The Sun shines on the Moon. – When the sunlight reflects off the Moon’s far

side, we call it a New Moon– When the sunlight reflects off on the Moon’s

near side, we call it a Full Moon– Between New and Full, we see parts of the

daytime side of the Moon.

Golfball and Blacklight Activity

11

Please do NOT use this to teach phases;

use to test for comprehension

http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question3.html

starchild.gsfc.nasa.gov/docs/StarChild/questions/phases.html

Eclipses

• The Sun and Moon occasionally line up so that we have an eclipse.

– These eclipses happen every year

– To see a solar eclipse, you need to be on a particular part of the Earth

14When the Earth’s shadow covers the Moon, we have a lunar eclipse

Three types of Lunar Eclipses

• Penumbral lunar eclipse—the Moon only passes through the penumbra of Earth’s shadow

• Partial lunar eclipse—part of the Moon passes through the umbra of Earth’s shadow

• Total lunar eclipse—the entire Moon passes through the umbra of Earth’s shadow

• Who on Earth will be able to see a lunar eclipse?

Anyone who can see the Moon (anyone who is on the nighttime side of the Earth during the eclipse)

Images from Fred Espenakhttp://www.mreclipse.com/LEphoto/LEgallery1/LEgallery1.html

Why is the Moon red during an eclipse?

• The Earth’s atmosphere filters some sunlight and allows it to reach the Moon’s surface

• The blue light is removed—scattered down to make a blue sky over those in daytime

• Remaining light is red or orange• Some of this remaining light is bent or

refracted so that a small fraction of it reaches the Moon

• Exact appearance depends on dust and clouds in the Earth’s atmosphere

Upcoming Lunar Eclipses

• June 15, 2011, Total lunar eclipse (not visible in US_

• Dec 10, 2011, Total lunar eclipse (mostly not visible in US)

• June 4, 2012, Partial eclipse • Nov. 28, 2012, Penumbral eclipse• Apr. 25, 2013, Partial eclipse (not visible in US)• May 25, 2013, Penumbral eclipse• Oct. 18, 2013, Penumbral eclipse• Apr 15, 2014, TOTAL ECLIPSE –visible here

19

Solar Eclipses• When the Moon’s shadow covers part of the Earth• Only happens at New Moon• Three types: Annular, Partial, and Total

Total Solar Eclipse• Observers in the “umbra” shadow see a total eclipse (safe to view the

Sun); can see the corona• Those in “penumbra” see a partial eclipse—not safe to look directly at Sun• Only lasts a few minutes• Path of Totality about 10,000 miles long, only 100 miles wide

Photo of a Total Eclipse

http://sunearthday.nasa.gov/2006/multimedia/gal_008.php

Annular Solar Eclipse• When the Moon is too far to completely cover the Sun—the

umbra doesn’t reach the Earth• Sun appears as a donut around the Moon

23

Photos of an Annular Eclipse

http://sunearthday.nasa.gov/2006/multimedia/gal_010.php; photos taken by Fred Espenak

Upcoming Solar Eclipses• Nov. 25, 2011, partial solar eclipse—not visible

in USA• May 20, 2012 (annular)—VISIBLE In USA• Nov. 13, 2012, total eclipse—not visible in USA• May 10, 2013, annular eclipse—not visible in

USA

• Next Total Solar Eclipse in continental USA—August 21, 2017

Tides

• The Moon’s gravity tugs on the Earth. – It pulls the most on the part of Earth closest,

which raises the atmosphere, the oceans, and even the rocks (a little)

– It pulls the least on the part of Earth that’s farthest, which allows the oceans and atmosphere to be further from the Moon (and higher)

– The Sun’s gravity does the same thing, but to a lesser extent

26

• St. Michel, N. coast of France

• ~16.8 m highest tidal range in Nova Scotia

27

Nova Scotia Tides

• Wolfville, NS (16 m tidal range)• Diurnal Tides (one high and one low

every 12 hours and 25 minutes

28

Sun and moon effects can be additive or not…

29

Force imbalance in earth-moon system creates tidal bulges

Tides and the Moon

31

• Second highest tidal range at Ancorage Alaska ~ 12 m