Transit of space station across the sun - 2 questions

Dear
"Alexander Thesoso" wrote in
message news:EOxQg.1276$xh.869@trnddc02...
I just stumbled across a photo of the transit of the
space station, and the shuttle across the sun.


http://www.astrophoto.fr/iss_atlantis_transit.html

Good photo. Thanks for the link!

I have two questions, each demonstrating my ignorance...

1) I don't see any sunspots... why not?

Upper right hand corner of the image... you have to scroll across
to it. Also, with the "local" detail to focus the ISS and
shuttle, smaller sunspots may be lost.

http://www.lmsal.com/YPOP/Projection...t_MDI_CON.html

2) I see a lot of limb-darkening. Why?
If the surface of the sun is isotropic,

It isn't, exactly.

isothermal

It isn't, exactly.

and the atmosphere is at least as hot as
the surface,

Again, it isn't exactly.

why the limb darkening?

http://en.wikipedia.org/wiki/Limb_darkening

David A. Smith