[Chaos-l] What's wrong with this picture?

[Jeff Polston]

The exact date according to my software is December 4, 2005.

The moon phase was about 16%.  Now, would earthshine be bright enough to look like a full disk, if exposed long enough?  I'm thinking the bright crescent "bleeds" enough to make it look like a disk, especially given the wide angle.  In other words, I don't think earthshine had a part.  I've taken shots of the moon that were over exposed enough for me to lose the phase and have it appear more full (granted, never at this small a crescent).

Jeff


-----Original Message-----
From: chaos-l-bounces at rtpnet.org [mailto:chaos-l-bounces at rtpnet.org] On Behalf Of D Gary Grady
Sent: Wednesday, April 23, 2008 12:53 AM
To: Chapel Hill Astronomical Observation Society
Subject: [Chaos-l] What's wrong with this picture?

NASA's latest Astronomy Picture of the Day is a bit surprising:

http://apod.nasa.gov/apod/ap080423.html

It appears to be a full moon setting next to Venus, which if you think
about it isn't possible.

The caption says the photo was shot in "early December of 2005," and per
http://aa.usno.navy.mil/data/docs/MoonPhase.php the new moon was
December 1, 2005, so one would expect the phase to be waxing, somewhere
in the neighborhood of the first quarter. Hence there's nothing at all
implausible about Venus being near the moon (and if I were feeling
better I might try figuring out the exact date using planetarium software).

So the real mystery is why the moon in the photo looks like a round
disk. I think the explanation is that in exposing enough to pick up the
Milky Way, we're seeing the dark side of the moon illuminated by enough
reflected earthshine to make it appear white. The part of the moon
illuminated by sunlight is of course far brighter, but in photography,
past a point white is white and adding more light doesn't make the image
any whiter.


--
D Gary Grady
Durham NC USA
dgary at mindspring.com
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