Not that its really important but I was merely using this as a source:
http://forums.dpreview.com/forums/re...hread=40880526
Also another post in the Canon forum of DPReview had a link to Amazon and it showed D800 as #1 and 5D mark iii as #2. These sorts of sales figures I imagine shift around. Also the D800 was announced earlier as well so that would play some part in it.
Not that its that important. What matters is getting the right camera for your needs. If you are wedding photographer with lots of Canon glass the new 5D mark iii would be an excellent choice.
But the post was about whether 5d mark iii makes sense for astrophotography and that's a different scenario.
As Fred pointed out if you are doing time lapse and want to use bulb ramping (gradually shifting exposure times to handle the change of light from day to night smoothly) then Canon is the way to go. If that is not important (and looking at Alex's time lapses for me I would think that is a minor detail) then D800 would be great.
As far as 36mp goes for time lapse I am of the opinion it would not benefit as you use wide field lenses anyway and the final image is downsized so much. A fast lens is more important than which camera.
As far as long exposure deep sky object astrophotography goes both will be great but you'd have to be pretty interested in the possibilities of a 36mp camera on a short focal length scope. Although at the end of the day it would need to be modified to be really good.
It'd be great if the top DSLR manufacturers made a camera with a detachable UV/IR filter and detachable low pass filter. I believe there is a lesser camera maker that already does that.
Both 5D mark iii and D800 are going to be super cameras. Objectively you have to admit Nikon has really taken a huge leap here and is the more revolutionary camera for now.
Greg.