What Happened to the Moon?

© Linda Davick

From: Our Franklin
Subject: Evening star scene
Date: January 29, 2009 4:28:24 PM PST
To: Marie, Linda, Elaine

Be sure to view the western sky at and after sunset.

From: Linda
What happens?

From: Our Franklin
The new moon (barely waxing) and the planet Venus put on a free show.

From: Linda on February 2
Venus is still up there and really bright but the moon has disappeared. What happened to it?

From: Our Franklin on February 4
Linda,

Regarding why the moon is in a different place from one night to the next:

The moon orbits Earth every 28 days or so, circling in the same direction as Earth's rotation (to our East).
Because the Earth is constantly rotating toward the East once every 24 hours, the moon appears to move across the sky toward the West along with Venus and all the stellar objects, "rising" in the East and "setting" in the West. This apparent westward motion is rather like the way we perceive the tops of trees and telephone poles seeming to race backwards as we lie in a moving car gazing up through the windows.

Like the trees and telephone poles, the stellar objects are relatively "stuck" in space, and it is we who move with the spinning Earth.
In reality, the stellar objects move along their own paths, yet since they are so terribly far away, their motion is practically undetectable to us. But unlike the stars and planets like Venus, the moon actually circles us. And since the moon is circling Earth much slower than Earth spins, the moon appears to lag behind by a few hours every night. (Actually, the moon, as seen from our perspective on Earth, is getting ahead of the other stars and such.)

If you observed the moon on a clear night for several hours, you might be able to notice this lagging behind the other background objects (Venus and the stars). And, as you have recently observed over several days , the moon definitely seems to be falling further "behind" the other objects.

Imagine your animated mouse friend on a carousel rotating counter-clockwise.
Surrounding the carousel is a circular train track.
On this track is a slow train called the Lunar Express, traveling the same way the mouse travels on the carousel.
But the carousel goes around many times while the Lunar Express makes only one full circuit along its track.
The mouse glimpses the Lunar Express briefly each time the carousel goes around.
Now across the track (on the outer side of the track) are a series of randomly placed "stellargraph poles" with stars on thars.
The train chugs steadily yet very slowly by these stellargraph poles.
The mouse sees the stellargraph poles beyond the Lunar Express.
To the mouse, both the Lunar Express and the stellargraph poles appear to be moving "backwards" as the mouse whizzes around on the carousel.
Each time around, the mouse notices that the Lunar Express has moved away from poles that were near the train last trip around.
Given enough cheese and a steady carousel ride, our mouse friend could easily imagine that the "outer world" of trains and poles is moving (clockwise) around her seemingly still carousel. And the stellargraphpoles would appear to be going around the mouse a bit faster than the circling train which really was going around the carousel in the other (counter-clockwise) direction.

Surely by now our mouse must be sleepy, or gone for more wine.
Good night.
RFL
RFL is Susan's husband, R. Franklin Landis (also known as Our Franklin)