Subject: Re: 4/11 *Black Box*
From: muffy@remarque.berkeley.edu (Muffy Barkocy)
Date: 1991-04-15, 10:06
Newsgroups: alt.tv.twin-peaks

In article <1991Apr15.153824.23535@watserv1.waterloo.edu> alternat@watserv1.waterloo.edu (Ann Hodgins) writes:

   In article <10360@mentor.cc.purdue.edu> russelrd@mentor.cc.purdue.edu (MattBrockman) writes:
   >In article <1991Apr14.191355.13625@watserv1.waterloo.edu> alternat@watserv1.waterloo.edu (Ann Hodgins) writes:
   >>Why are you sure its an eclipse and not  the moon being eclipsed by the
   >>earth, creating the phases of the moon?
   >
   >The phases of the moon are NOT caused by the moon being eclipsed by
   >the earth. This happens only rarely and is called a Lunar Eclipse.
   >
   >The phases of the moon are just how much of the light side
   >of the moon we see compared to how much of the dark side
   >we see.

   Actually this has bugged me for a while.  What makes the moon light?  -
   reflecting sun light. What causes the dark side?  - as far as I know it
   is the earth interfering with the light getting to the moon. Technically
   not an eclipse I guess, but very similar in effect - one planetary body 
   interfering with the light coming off another body.

   ann

No, the dark side of the moon is caused by the *moon* interfering with
the light getting to the moon.  That is, the light is coming from the
sun, it gets to the moon, lights up one side.  The moon is a sphere, so
we can only see half of it and the sun only lights half of it.  This is
not necessarily the same half, depending on the relative positions of
the earth, sun, and moon, which is why we see phases of the moon.

If this is still confusing, take a ball, hold it near a light, and
notice that the light can only reach half of the ball, the other half is
shaded by the ball itself.  If you look at the ball from different
positions, you will see different combinations of light and dark.

Note that the lighting of the moon requires only two bodies, the moon
and the sun.  The phases require an observer, but not a third body.  An
eclipse, on the other hand, is, as you say, caused by one body
interfering with the light from another body to a third body.

Muffy