DES Today

1
DES Today!

• Challenge Why does the moon look different
  throughout the month? Be specific!
• Quiz What would be different on earth if we had
  no moon? (Pick anything from the video there
  are many correct answers!)

2
DES Today!

• Challenge How would our moon phases change if we
  lived in Australia and why?
• Quiz What is the difference between a crescent
  and a gibbous moon?

3
Earth, Sun and Moon Systems
Earth, Sun and Moon Systems
www.starmanproductions.com
4
Reviewing Shadows

• When you hold a light source FAR from an object,
  the object only blocks a little light, so its
  shadow is SMALL and SHARP.
• When you move the light source CLOSE to the
  object, the object blocks a lot of light and its
  shadow is BIG and FUZZY.
• http//www.phy.ntnu.edu.tw/java/shadow/shadow.html
  

5
About Our Moon

• Probably formed when a large object hit Earth and
  broke off a piece.
• The moon is about ¼ the size of Earth
• It takes about 27.3 days to orbit Earth
• About 386,000 km from Earth

6
(No Transcript)
7
Phases of the Moon

• The Moon itself does not emit any light We see
  the Moon because it reflects sunlight back toward
  us.
• As the Moon circles the Earth, the amount of the
  lit side we see changes, which creates the daily
  phases.

Yes, phases of the Moonillustrated using
deliciousOreo cookies!
8
Important Moon Phase Terms

• Waxing Changing from new moon to full moon (2
  weeks). As we see more of the moon we call the
  phases waxing.
• Waning Changing from full moon back to new moon
  (2 weeks). As we see less of the moon we call
  the phases waning.
• Crescent see less than half the moon
• Gibbous see more than half the moon
• At the 1st and 3rd Quarters, we see exactly half
  of the moon.

9
Phases of the Moon
10
Phases of the Moon
11
Dark Side of the Moon?

• Why does the moon have a dark side? Why does the
  illuminated side always look the same (the moon
  revolves, after all!)
• Physics Connection! Its synchronous rotation.
  The time it takes the moon to rotate once on its
  axis is the same as the time it takes it to
  revolve around the Earth.
• Cause? Earths tidal force or differential
  (uneven) gravitational force on the Moon.

12
DES Today!

• Challenge How can our tiny little moon
  completely block out our massive sun?
• Quiz What is synchronous rotation and how does
  it explain why we always see the same side of the
  moon?

13
From the Moon to Eclipses
14
The Lunar Eclipse!
15
Lunar Eclipses
16
Some Basic Terms

• a. Umbra
• -darker, central region of the Earths shadow
• b. Penumbra-
• fainter outer region of the Earths shadow

17
Partial vs. Total Lunar Eclipse

• A lunar eclipse happens during a FULL MOON when
  the Moon passes through the Earths shadow.
• TOTAL Lunar Eclipse You see a total lunar
  eclipse when the Moon is in the darker central
  region of the Earths shadow (umbra).
• PARTIAL Lunar Eclipse You see a partial lunar
  eclipse the Moon is in the fainter outer region
  of the Earths shadow (penumbra).

18
Model of a Lunar Eclipse
www.salagram.net/eclipses-page.htm
19
Other Notes Lunar Eclipses

• Only happen when the moon is in full moon
  position
• Can last for several hours
• Happen slightly more often than solar eclipses
  (3-4 times per year)
• The moon never fully disappears, but instead
  turns red in color

20
Why the Moon looks red
21
(No Transcript)
22
Close up of a Lunar Eclipse
23
Its All About Your View
24
When can we see a lunar eclipse?

• Next penumbral lunar eclipse seen from North
  America March 16, 2006 (very hard to see!!!)

http//sunearth.gsfc.nasa.gov/eclipse/LEplot/LEplo
t2001/LE2006Mar14N.GIF
25
When can we see a lunar eclipse?

• Next total lunar eclipse seen from North America
  March 03, 2007

http//sunearth.gsfc.nasa.gov/eclipse/LEplot/LEplo
t2001/LE2007Mar03T.GIF
26
The Solar Eclipse!
27
Solar Eclipse
The next full solar eclipse in North America
will be in 2017.
28
Solar Eclipse

• a. Umbra
• -dark, central region of the moons shadowfrom
  where you can see a total eclipse
• b. Penumbra-
• -fainter, outer region of the moons shadowfrom
  where you can see a partial eclipse

29
(No Transcript)
30
Partial vs. Total Solar Eclipse

• A solar eclipse happens during a NEW MOON when
  the Moon lies directly between the Earth and Sun.
• TOTAL Solar Eclipse You see a total solar
  eclipse when you are located where the Moons
  darkest shadow falls on Earth (umbra).
• PARTIAL Solar Eclipse You see a partial solar
  eclipse when you are located where the Moons
  lighter shadow falls on Earth (penumbra).

31
Model of a Solar Eclipse
www.salagram.net/eclipses-page.htm
32
Why dont eclipses happen every month?
33
Why dont eclipses happen every month?

• The moons orbit around the Earth is tilted at 5
  degrees compared to the Earths orbit around the
  sun.
• Therefore, the moon, Sun and Earth are not
  perfectly lined up every new or full moon to
  create an eclipse.

http//observe.phy.sfasu.edu/courses/ast105/lectur
es105/chapter02/moon_orbit_tilt_vs_ecliptic.htm
34
Other Notes, cont

• Only lasts a few minutes (totality)
• Happens 2-3 times per year

http//highered.mcgraw-hill.com/sites/0072482621/s
tudent_view0/animations.html -Chapter 9,
Eclipses animation
35
Special Eclipses

• The Moons distance from Earth changes during the
  year, and when it is farthest away (at its
  apogee) it looks smaller.
• If an eclipse happens at this point, the moon
  looks too small to completely block the sun, so
  you see an annular eclipse.

36
Other Notes, cont
37
http//www.fourmilab.ch/earthview/pacalc.html
Apogee-The point when the moon is at its farthest
from Earth each month Perigee-The point when the
moon is at its closest to the Earth each month
252,700 miles
221,500 miles
38
(No Transcript)
39
When can we see a solar eclipse?
You are here!

• Next total solar eclipse that can be seen from
  North America
• August 21st, 2017

40

• Closest Viewing of the Total Eclipse
• St. Louis at noon

41
When can we see a solar eclipse?

• Next total solar eclipse that can be seen near
  Chicago
• September 14th, 2099

http//eclipse.astronomie.info/sofi/activemaps.htm
l
http//sunearth.gsfc.nasa.gov/eclipse/SEplot/SEplo
t2051/SE2099Sep14T.GIF
42
When can we see a solar eclipse?
You are here!

• Next partial solar eclipse that can be seen from
  North America
• June 1, 2011

43
When can we see a solar eclipse?
You are here!

• Next annular solar eclipse that can be seen from
  North America
• May 20th, 2012

44
(No Transcript)
45
Predicting Eclipseshttp//www.math.nus.edu.sg/asl
aksen/gem-projects/hm/0102-1-stonehenge/eclipses.h
tm
46
The Seasons!
47
Our Tilted Little Planet

• To the ancients it seemed the sun changed
  positions in the sky throughout the year.
• Sun was higher in the sky in Summer (NH)
• Sun was lower in the sky in Winter (NH)
• We now know that the suns position is fixed
  its the tilt of our planet that affects the
  seasons and where the sun appears in our sky.

48
(No Transcript)
49
Why the Tilt?

• Scientists believe that the sun and the nine
  planets formed by chunks of rock and debris that
  self-accumulated through gravity. In other words,
  objects collided and clumped together, which
  increased their gravitational pull, which in turn
  drew more objects in, which made the object even
  more gravitationally powerful, and so on until
  the solar system looks like a sun and nine fairly
  neat planets with not much stray junk flying
  around. Scientists believe Earth was smacked
  hard enough (probably more than once) to tilt its
  axis!

50
And the Tilt Does What?

• The tilt (23?) means we either face into the sun
  (summer) or away from the sun (winter) over the
  course of a year.

51
And That Affects Daylight How?

• The region tilted towards the Sun is warmer
  because sunlight travels more directly to the
  Earths surface and less gets scattered in the
  atmosphere (longer days).
• The region titled away from the Sun is cooler
  because the light reaching it is indirect or
  more scattered (shorter days).

52
FYI Climate and Latitude

• Places far from the equator receive less sunlight
  than places close to the equator.
• Coldest at the poles and high altitudes (least
  sunlight)
• Warmest at the equator (most sunlight)
• Mid latitudes. Climates are affected by both
  warm, tropical air moving towards the poles and
  cold, polar air moving towards the equator.

53
Solstice vs. Equinox

• Solstice Occurs twice a year when the Sun is at
  its greatest distance from the celestial
  equator. (Summer and Winter)
• Equinox Occurs twice a year when the Sun
  crosses the plane of the Earths equator making
  day/night of equal length. (Spring and Autumn)

54
Solstice in the Northern Hemisphere

• Summer (June 21)
• The sun is at its zenith at the Tropic of
  Cancer.
• Winter (Dec 21)
• The sun is at its zenith at the Tropic of
  Capricorn.

55
Equinox in the Northern Hemisphere

• Vernal (March 21)
• Autumnal (Sept 21)
• Notice they look basically the same!
• Equinox literally means equal nights

56
Compare their Positions
57
So What Did We Learn?

• Moon phases occur because of how we see
  reflected sunlight.
• We have seasons because of our tilted axis.
• Solar and lunar eclipses, solstices, and equinox
  occur because of the relative positions of the
  Sun, Earth and Moon.
• Celestial bodies appear to change positions in
  the sky because we move!

58
And Where Are We Going Next?

• We will explore how understanding optics helps
  us see beyond our planet.
• We will revisit wave properties and study
  reflection and refraction of light.
• We apply the Doppler Effect to measure the
  Universe.