Astronomy Rough Notes – Cycles of the Sky 1: Moon
BRING:
Curtain
Earth globe
Tennis ball and stand
Sun lamp
Orrery
Styrofoam balls with pencils
DISCLAIMER: These notes do NOT cover everything you need to know. You may need to look
up some item or concept online or in a text. Test questions are not exact copies of the
OBJECTIVES but if you know the OBJECTIVES thoroughly, you should do well on the exams.
OBJECTIVES
 Explain why the Moon exhibits phases. Draw the Sun-Earth-Moon system showing the
Moon’s orbit (not to scale), draw Moon in several different positions in its orbit and shade
in Earth and Moon indicating which side is lit and which is dark. Use that drawing to
explain what phase you will see for each of the Moon’s locations you drew.
 Predict the approximate time of day/night you should look for first quarter moon, full
moon, last quarter moon. Explain your thinking using a sketch of the Earth-Moon-Sun
system.
 Knowing when new Moon occurs, predict about when first quarter, full, and last quarter
Moons will occur.
 Explain why the Sun, Moon and stars appear to rise in the east and set in the west.
Explain why we have day and night using a sketch of Sun-Earth-Moon system to help.
 In one hour, the Moon, Sun, and stars move about how many degrees on the sky? How
can you easily calculate that number (hint: how far does the Earth rotate in 24 hours)?
 In one day, Moon moves about how many degrees on the sky? How can you easily
calculate that number (hint: about through how many degrees does Moon revolve in 30
days)?
 What direction does the Moon move from one night to the next? Explain?
 What is a mare?
 What causes craters, especially on the Moon?
 What is the Moon’s terminator?
 Explain how astronomers think the Moon formed and give evidence.
 Explain why you always see the same face of the Moon.
 What causes a solar eclipse? What causes a lunar eclipse?
 Use the terms rotation and revolution correctly.
Rev. 1/17/2017
CLASSROOM: Moon’s Phases
1. What we see from Earth from night to night
 Model with Starry Night (watch for phase)
Notice:
Phase Name
Appearance
New
Waxing Crescent
First Quarter
Waxing Gibbous
Full
Waning Gibbous
Last Quarter
Waning Crescent
2. What we see from space from night to night
 Model with Solar System
 Model with globe, tennis ball and sun lamp
 Draw it (as below or see text or
http://www.noao.edu/education/phases/phases_demo.html or
http://www.inconstantmoon.com/cyclopedia.htm )
 Explanation
o Moon is always half lit by Sun
o Our perspective from Earth of the lit half gives us phases.
 Ex – Full moon = we see all of the lit half
 New moon
= we see none of the lit half
 Quarter moon = we see half of the lit half
Rev. 1/17/2017
EARTH VIEW: From Earth’s
perspective, we see a small
portion of the right side of the
half lit Moon.
ALIEN VIEW: Half lit Moon seen from
outer space
Picture from http://www.itc.csmd.edu/bio/georgek/moon%20phases.bmp
More here: http://www.astro.umass.edu/~myun/teaching/a100/longlecture4.html
3. Construct above drawing from scratch….
4. Tutorial: Moon Phases (emailed to you - If you did not fill in an email form on day 1, email
me asap)
Due date for the Moon Phases exercise is on the calendar.
General Comments on Motion
 Everything is in motion
 Some objects too far to see the motion easily (stars)
 Some motion complicated by observing from a moving system (Moving Moon and moving
planets viewed from moving Earth)
Rev. 1/17/2017
Motion You Can See (Especially the Moon’s Motion)
1. Sun, Moon, Stars - What do we see?
a. Minute to minute
Demo with Starry Night (Don’t just believe the software, go outside and check!)
You see Moon (and stars and planets and Sun) rising in the east, moving west
b. Day to day (night to night)
Demo with Starry Night (I will ask you to check me on this one.)
You see the Moon move noticeably toward the EAST!
Stars (and planets) seem to move slightly west.
2. What is moving and how much?
a. Earth rotates 3600 in one day
How much does Earth rotate in one hour?
~3600/day = 3600/24 h = ~150/h
b. Moon revolves 3600 in one month
How much does Moon revolve in one day?
~3600/month = ~3600/30 days = ~120/day
Which happens quicker Earth’s rotation or Moon’s revolution?
150/h is much quicker than 120/day
so you will see the Earth’s rotation much sooner than Moon’s revolution
Moon’s
Orbit
Moon revolves
~120 in 1 day
Sun
Earth rotates
3600 in 1 day
3. Which direction will Sun, Moon, and stars move in one hour?
Look down on solar system. See next diagram.
Sun rotates counterclockwise (ccw). Earth and Moon rotate and revolve ccw.
Consider Earth’s rotation.
You are looking down on the N pole of Earth.
Rev. 1/17/2017
Therefore Earth is rotating toward the East (think about where the US would be on the globe
and where east and west are).
Therefore Sun, Moon, planets will rise in east and move to west.
Conclusion: In one hour, Sun, Moon, stars will appear to move about 15 0 toward the west.
Check it out: I won’t ask you to turn anything in but note where a bright star is and then look an
hour later to see if it has moved about 150 west.
Moon’s
Orbit
Earth
revolves
Earth
rotates
N
Moon
rotates
Sun
rotates
Sun
NOT TO SCALE!
Moon
revolves
4. Which direction will Moon move from one night to the next?
Moon’s
Orbit
Moon revolves
~120 in 1 day
Sun
Earth rotates
3600 in 1 day
Rev. 1/17/2017
In one day, the Earth rotates back roughly to where it was the night before.
The Moon, however, has moved ~120 east in that time.
5. Summary:
 Earth rotates quickly (24 h), Moon revolves slower (1 month), stars seem fixed (very far
away)
 Earth’s rotation causes Sun, Moon, stars to rise in east and set in west (~150 per h)
 Moon’s revolution to the East can be seen from night to night (~120 per day)
Moon Picture – What do you notice?
http://www.astronomy.org/StarWatch/January/1-15-08-moon.jpg
Or
http://antwrp.gsfc.nasa.gov/apod/ap001228.html
See
Craters, Mare, Terminator, Phases
Details near terminator
Project: Moon Craters – See calendar for instructions and possible opportunities.
Solar and lunar eclipse
Solar eclipse explained at many sites. For example,
http://www.windows2universe.org/sun/atmosphere/solar_eclipse.html
http://sunearth.gsfc.nasa.gov/eclipse/ for eclipse data
Origin of Moon
Early Earth and Mars size object collide
Moon’s composition is like that of Earth’s crust
Back side does not have maria like the Earth side
Not much if any iron core
More at http://www.psi.edu/projects/moon/moon.html
Or here http://www.seti.org/node/1458
And a movie here http://stewartlab.rc.fas.harvard.edu/moon/GiantImpact2.mov
More “Lunatics” that we may not have had time to cover but that you should know.
For general Moon nonsense, see http://www.badastronomy.com/bad/misc/index.html
I. Are you nuttier at Full Moon? Nonsense. See
http://skepdic.com/fullmoon.html
or http://media.skytonight.com/documents/200701051052N.pdf
II. Moon Illusion
1. Size comparison http://antwrp.gsfc.nasa.gov/apod/ap011015.html
2. Full Moon over Greece http://antwrp.gsfc.nasa.gov/apod/ap050623.html
3. No real change in size (sequence photo)
http://antwrp.gsfc.nasa.gov/apod/ap050503.html
Or
http://www.nasa.gov/vision/universe/watchtheskies/20jun_moonillusion.html
Rev. 1/17/2017
4. Big Moon Illusion (it’s your brain playing tricks
http://www.badastronomy.com/bad/misc/moonbig.html
5. Moon size does change but you cannot notice it (Moon gets slightly closer and farther)
http://antwrp.gsfc.nasa.gov/apod/ap041021.html
III. Moon’s Libration
Full lunar cycle (with libration) http://antwrp.gsfc.nasa.gov/apod/ap040829.html
IV. Rotate vs revolve
1. Moon shows same face to us (mostly) – See Libration photos
Far side photo (from spacecraft): http://antwrp.gsfc.nasa.gov/apod/ap070225.html
2. Moon gravitationally locked to us
3. Moon rotates and revolves at same rate
Miscellaneous
Some general websites:
http://www.inconstantmoon.com for lots about the Moon
http://antwrp.gsfc.nasa.gov/apod/astropix.html then search for Earth’s Moon under Index or
Search
Free Moon Software (for craters, mare, etc)
1. “Virtual Moon Atlas” Download from http://www.astrosurf.com/avl/UK_index.html
2. “Photographic Moon Book” Large! 225 page 105 megabyte PDF
http://www.cityastronomy.com/moonbook-mirror.htm
“This page is a courtesy North American downloading mirror for Hong Kong based
amateur Alan Chu's superb "Photographic Moon Book". For those unfamiliar with this free
publication, it is a photographic guidebook to the moon containing nearly 300 annotated
images of lunar features with complete feature descriptions in 33 map sections--- and too
much more useful information to list here. It is an excellent (I feel the very best available,
free or otherwise) observer's guide to our Moon. This is the most recent version, released
Jan. 2007.”
Free Solar System Simulator Software
http://sssim.com/en/product/index.html
Homework:
 Read web or text about Moon phases, Moon craters, eclipses
 Read web or text about origin of Moon
 Make flash cards or write out your answers to the objectives covered to this point.
 Work the Moon Phases tutorial and hand it in.
 Plan how you will observe the Moon so you can do the Moon Craters exercise.
Rev. 1/17/2017