"Alan LeHun" wrote in message
...
In article . com,
says...
Some shots from the evening of March 1st 2006
Earthshine
http://www.digitalsky.org.uk/2006-03-01/earthshine.html

Those are stars visible in the background, correct?
At what phase would the moon's brightness make
them not show up in photographs?


The exposure for that shot was such that the Earthshine could be imaged.
A whole 1 second with very fast film. Look at how bleached the actual
crescent is. Had the shot been taken with an exposure to show the
crescent then the crescent would be all that was visible. It's not a
question of brightness per se but of exposure.

IOW it is already too bright to show the stars if it is the sunlight
side you want to image.


I just did a quick back of the envelope calculation. It looks like the
surface brightness of the illuminated moon is roughly the same as a 0
magnitude star assuming 3arcsec seeing. Given that the minimum detectable
in an image is say 1/100 th of that value, that would suggest that it should
be possible to detect a mag 5 star with a correctly exposed moon. This
assumes though that the scale is such that the star covers at least one
pixel, which is probably not the case in Pete's image

Robin