moon ~ earth ~ sun

O, swear not by the moon, the fickle moon, the inconstant moon, that monthly changes in her circle orb, Lest that thy love prove likewise variable –- Shakespeare's Juliet speaking to Romeo, Act 2, Scene 2.

And if she faintly glimmers here,
And paled is her light,
Yet alway in her proper sphere
She's mistress of the night. –- Henry David Thoreau, 1843 — 1916

Inconstant Moon or in Her Proper Sphere?

To understand the moon’s predictably peripatetic motion, let’s first focus on the eastward (west to east) rotation of the earth. Later we will look at how this affects apparent movement of sun and moon, and, in a future topic, the actual movement of tides and winds (Coriolis effect). We are setting a foundation for understanding time zones, International Dateline, moon, tides, and weather. 

It all starts with the earth’s rotation.

The sun also ariseth,
And the sun goeth down,
And hasteth to his place where he ariseth. –- Ecclesiastes 1.5. JPS 1917 translation

After night, we see the sun rise in the east because we move with the earth eastward toward sunlight. After noon, our eastward journey takes us away from the sun until the western horizon rises up to obscure the sun at nightfall. 

In contrast to this actual earth rotation, we experience an apparent transit of sun moving westward (east to west) rising from the east and setting in the west. While we know the earth is moving eastward, it is convenient and conventional to speak of the sun transiting westward.

The moon also rises and sets. The moon, like the sun, rises in the east and sets in the west. If you see the moon above the eastern horizon, it must be rising. If you see the moon above the western horizon, it must be setting. The apparent motion is always from east to west. If that seems too obvious to say, consider this tale of my confusion.

On night watch in 2006 on a voyage to the Marquesas, I saw predawn clouds glowing red, and immediately thought of welcoming dawn. The moon, having been hidden all night by storm clouds, was not on my mind. 

Slowly, to my sleep deprived mind, the “dawn” I was expecting was occurring in the west. 

Had I missed a gap of time, was this sunset instead of dawn? 

All I could think of was the sun. It felt like the end of the world.“What is going on?” I asked myself. 

Slowly the facts became clear. The storm clouds had parted at the western horizon, revealing a blood red full moon setting there. Soon after on the eastern horizon came rosy-fingered dawn (The Odyssey).  

There had been no apocalypse when “the sun became black as sackcloth of hair, and the moon became as blood;  And the stars of heaven fell unto the earth.” (Revelation 6, 12 & 13, King James translation). 

Let us now compare sun with moon.

Petruchio. ... Good Lord, how bright and goodly shines the moon!
Katherina. The moon? The sun! It is not moonlight now.
Petruchio. I say it is the moon that shines so bright. 
Katherina. I know it is the sun that shines so bright.
— Shakespeare’s “The Taming of the Shrew”

SUN 

1. By dictionary definition, one day is 24 hours from one midnight to the next.
2. One sunrise and one sunset occur each 24 hours.
3. Seeing when the sun is above the horizon is as obvious as the difference between night and day.
4. The earth revolves about the sun.  See “Galileo's Daughter: A Historical Memoir of Science, Faith, and Love” by Dava Sobel  http://a.co/8UsrOu1

MOON

1. The moon rises about 50 minutes later each day. Either think of it as lazy or understand that the earth rotates a little more than one full rotation to go from one moonrise to the next.
   • ​Easy: http://earthsky.org/moon-phases/understandingmoonphases 
   • More complete: http://star-www.st-and.ac.uk/~fv/sky/moon-general.html
2. Generally one moonrise and one moonset occur each day. Some days miss a rise or a set. What is missing can be found soon after midnight within the first hour of the next calendar day. As days progress, the moon rises later each day. The time of rising will move backwards though all 24 hours of nighttime and daylight.
3. The moon revolves about the earth creating moon phases described below.
4. When the moon is above the horizon, it is always visible at night and sometimes visible in daylight. The new moon is never visible because it rises and sets with the sun which lights up our day but does not light up any portion of the moon facing us. (See 5. below). The full moon is visible all night and never in the day because it rises at sunset and sets at sunrise. In the week before a full moon, the waxing gibbous moon rises before sunset. Look for it in the east in the afternoon. In the week after a full moon, the waning gibbous moon sets after sunrise. Look for it in the west in the morning. http://earthsky.org/space/when-can-you-see-a-daytime-moon
5. One hemisphere of the moon is called the “far side” because it always (see notes 1 & 2) faces away from earth, staying out of sight. There is no “dark side of the moon” notwithstanding the Pink Floyd album by that name. The far side gets as much sunlight as the earth-facing side. See “The Far Side of the Moon: A Photographic Guide” by Charles Byrne http://a.co/hBt8ayu

Note 1 on Tidal Locking: https://en.wikipedia.org/wiki/Tidal_locking
Note 2 on Libration: https://en.wikipedia.org/wiki/Libration

Here is a sequence of moon phases.
https://science.nasa.gov/science-news/science-at-nasa/2002/12apr_earthshine
https://earthobservatory.nasa.gov/IOTD/view.php?id=83782

New – Not visible. Up all day. Rises and sets with  the sun.

Early WAXING CRESCENT. Rises soon after sunrise and sets soon after sunset. Here after sunset with earthshine (light reflected from earth).

Early Waxing Crescent

WAXING CRESCENT. Rises before noon and sets before midnight.

Waxing Crescent

FIRST QUARTER. While one half of the whole moon is receiving sunlight, half of that sunlit moon is on the far side of the moon not visible to earth. From earth, only a quarter of the moon is seen in sunlight.  Think of a quarter section of an orange. Rises at noon, highest at sunset, sets around midnight.

First Quarter

WAXING GIBBOUS. Rises in late afternoon before sunset. Up through most of the night. Sets before sunrise. To see it in daylight, look to the east in the afternoon to see it rising.

Waxing Gibbous

FULL. Up all night from sunset to sunrise. The entire earth facing hemisphere is sunlit.

Full Moon

WANING GIBBOUS. Rises after sunset and is up for the rest of the night and into the morning. Sets after sunrise. To see it in daylight, look west after sunrise before it sets.

Waning Gibbous

THIRD QUARTER. Rises at midnight, highest at sunrise, sets around noon.

Third Quarter

WANING CRESCENT.  Rises before dawn and is up for most of the day, setting before sunset.

Waning Crescent

​Summary chart of the moon phases

We have compared the sun and moon and then looked at moon phases. To prepare for studying tides in a latter article, think now of moon and sun together. Here is a diagram from Bowditch Chapter 15, “Navigational Astronomy”, Section 12 “The Moon” pages 223 to 224 available from the Maritime Safety Office of the National Geospatial-Intelligence Agency at:
http://msi.nga.mil/MSISiteContent/StaticFiles/NAV_PUBS/APN/Chapt-15.pdf
as copied below with permission for non-commercial use.
http://msi.nga.mil/NGAPortal/MSI.portal?_nfpb=true&_pageLabel=msi_comm_use_warning

What matters for tides is to see that with a New Moon and Full Moon the moon and sun are on the same line which makes for greater tidal change (spring tide). The name for this with a New Moon is “conjunction” (moon between sun and earth) and the name with Full Moon is “opposition” (moon on opposite side of earth from sun). The quarter moons are at a right angle to line between earth and sun (quadrature) making for least tidal change (neap tide).

For a more detailed diagram with further explanation see: http://www.moonconnection.com/moon_phases.phtml

For a web moon phase calendar see:
http://www.moonconnection.com/moon_phases_calendar.phtml

For $29.95 you can purchase moon phase predicting software (for Windows or Mac) at
http://www.quickphase.com/

The software author makes the same functionality available for free for cell phones. http://www.lunasolaria.com/
For a bio of the software’s author see 
https://www.bluemarmot.com/about.phtml?ws=bm
https://www.bluemarmot.com/

If you want tables of moon and sun rise and set times, the Navy provides them (in Standard Time only): http://aa.usno.navy.mil/data/docs/RS_OneYear.php
To see media’s earth rotation direction blunders: http://ew.com/article/1992/03/13/earths-rotation/

To learn more about moon phases and check my writing for errors:
http://earthsky.org/moon-phases/understandingmoonphases
https://svs.gsfc.nasa.gov/4236
http://www.astronomy.com/magazine/ask-astro/2015/09/moonrise-times
http://curious.astro.cornell.edu/about-us/46-our-solar-system/the-moon/observing-the-moon/128-how-does-the-position-of-moonrise-and-moonset-change-intermediate

A final thought:
If the illuminated portion of the moon as seen from Southern Hemisphere is on the left side of moon, then in the Northern Hemisphere it will be seen on the right, and vice versa.

http://moongazer.x10.mx/website/astronomy/moon-phases/
http://curious.astro.cornell.edu/about-us/46-our-solar-system/the-moon/observing-the-moon/135-does-the-moon-look-different-in-the-northern-and-southern-hemispheres-beginner

Consider the following two related matters:

The confusion of perspective is why starboard is a name used for an actual side of a boat as compared with the concept of “right” which changes with the perspective of the observer. Avoiding confusion is critical in avoiding collisions at sea.

​Cyclones spin in opposite directions on opposite sides of the equator.  This is something to examine in future articles.