Space Forum / Shuttle / May 2007

I remember one of the early astronauts (from
Mercury, IIRC) describing looking down on
Africa at night and seeing campfires.

One of the rules of thumb from photographic
lighting is that, for extended objects (not point
light sources), the observed surface brightness
is independent of distance.  That's because
both the observed angular area and the total
brightness vary with the inverse square of
distance, so the brightness per unit angular
area stays constant.

If that doesn't make sense, here's a
more relevant illustration of the
point:  If you've ever flown in an
airliner at night, you'll notice that cities near
the horizon appear about as bright as cities
directly below you, assuming they're
relatively equally densely populated and
equally lit.  And cities near the horizon
from a 35,000 ft airliner are at close to
the same distance as cities directly
below an orbiting spacecraft.

I've never been in an orbiting spacecraft,
but I'd expect that, once you're on the
dark side of Earth, if your interior
lights are suitably dimmed and your
eyes are properly dark-adapted, it
should be easy to pick out cities
at night.

I am not sure about city lights, but I have talked to astronauts that have
told me lightening/thunderstorms are VERY visible from orbit.  Michael
Collins also mentions this in his book.

Danny Deger

There's that composite photo of the USA at night, taken with DOD
satellite cameras (the weather one, IIRC).  One of the filenames you
may find this under is "nightlights-081503-0103z.jpg" (although my
copy is just the NE states).  I think there is also some post-Katrina
pix showing how the Gulf Coast stayed in the dark.

True, satellite cameras often have better resolution than the human
eye, but they are also often farther out, so I think there's a lot of
opportunity for spotting cities, and maybe towns.

/dps