How Visible Will ISS (Babylon) Be???
Bruno Tilgner (Bruno_Tilgner@compuserve.com)
Mon, 21 Dec 1998 16:07:39 -0500
James Husnay Sr. asked:
>Will it be possible if conditions are at their best, does anyone know
>if there is a chance we would be able to see the ISS/Babylon's actual
>structure "Naked eye"?
Absolutely not. The largest extent of ISS will be 358 ft or 109 m. At
a distance of 400 km, i.e. for a zenith pass, this means an angular size
of 2.73 * 10^-4 rad or 56.3 arcsec. This is for the entire station. In
order to see the *actual structure* much smaller details must be resolved,
say in the order of 10 arcsec and less.
The human eye can resolve details of about 120 arcsec. Although this number
depends on wavelength and contrast, it is a good first approximation. This
means a difference of at least an order of magnitude. So, no way to see
any *actual structure* naked eye.
Whether structural details will be visible with telescopes is a different
matter. Experience with Mir, whose largest dimension is about one third that
of ISS, suggests that it will be very difficult at best. The main problem
is "seeing", i.e. blurring by atmospheric turbulence. But with professional
equipment it can be done, even by daytime. See Ron Dantowitz's article in
the August 1998 issue of SKY & TELESCOPE, p.48.
Bruno Tilgner
Paris, France