The following is a quick excerpt transcripted from the 2:30 pm EDT NASA LCROSS Day-1 audio press conference (10-8-2009). The transcript may contain errors.  The transcript excerpt concerns principal co-investigator Colaprete's comments on plume brightness, target selection and recommendations (to the general press) on public observing: --------------------------- Tony Colaprete (statement and answer to follow-up question) "There was a serendipitous situation for use.  For our impact date - tomorrow morning - the sun will be shining through a cleft - a valley - right along the rim of the [Cabeus proper] crater.  This valley let's sunlight - it streams across the crater floor - 500 or 1000 meters above the valley [sic - Cabeus crater] floor.  So our ejecta actually gets into sunlight quite early - only after a kilometer of rise. That's great news.  . . . .  One other aspect that made it [Cabeus] more attractive was the backlighting.  Cabeus A would have had a bright crater wall behind the Earth observers.  . . . . With this new particular Cabeus target, that valley that spreads light in, the farside of that valley actually casts a shadow behind where we are impacting. So you have a large black shadow acting as a backdrop for the observations from Earth.  So you get a very high contrast. And so it just worked out perfectly for us. . . . ." "It's not going to be a grand spectacle. . . . It will last at its brightest for about 30 seconds. And it will be a about a factor of 5 or so or maybe 10 times dimmer than the surface of the Moon itself.  So, it will be dimmer than the Moon.  That's why the black background is important and is needed because it provides a high contrast.  What a somebody looking through a 10 or 12 inch telescope might see is essentially a fuzzy or a sparkling shimmering across this black space on the Moon - this shadow that essentially extends from the ridgeline of what's called Malapert 1 - M1 - that's that mountain between us - between the Earth and our impact site - extending down towards the south pole of the Moon you will see this stripe - that black shadow - and across that you will see a shimmer that will last about 30 seconds.  Essentially - basically - you will see the blackness get less black as the ejecta moves across in front of it and falls back to the surface. So, the hardest thing, actually, and this is true even for the professional astronomers - the hardest thing is to find that shadow and find that crater.  So, we've been careful of that - if you are going to look at this the best place to observe it is probably online - on NASA TV, because we will have cameras on the shepherding satellite that is following it in - and will be looking. We will be streaming those to the television to the internet, so you will be able to see those and watch in the comfort of your own home. We know where the crater is, we've been looking for it and we will be real up and close.  Otherwise, go to one of these observing parties that Jen [Dr. Jennifer Heldmann] mentioned.  Again, it takes practice finding a crater on the moon and in particular finding a particular particular shadow next to a crater on the moon. So, really, I advise people to get online and find a event and go and witness it that way or just watch it, again, on their TV or their computer." End Excerpt Transcript  ------------------ Notes by Kurt - "[A] factor of 5 or so or maybe 10 times dimmer than the surface of the Moon" implies the curtain will be 1.7 to 3.8 differential mags dimmer than the surrounding surface.  Colaprete does not describe absolute magintudes or provide a baseline surface brightness.  Assuming these refer to mpsas and using a 3.8 mag surface brightness, these imply a plume brightness of 5.5 mpsas to 6.3 mpsas. The cleft valley through which sunlight will stream into the bottom of Cabeus can be seen on aerial view finders at this url: http://lcross.arc.nasa.gov/observation.htm Clear Skies and Happy Imaging - Kurt