hi Conor/Bart,
hope you don't mind if I suggest a small correction to the explanation?
the reddish band is actually the upper part of the Earth's atmosphere continuing to be illuminated by sunlight. The lower greyish part is the Earth's shadow rising. Depending on the amount of aerosols in the atmosphere the colour tints can be quite dramatic. Obviously, at this time of year with the Sun dipping far below the horizon at night, the Earth's shadow is higher in the night sky (which is why we see less artifical satellites at this time of year, because a lot of them are orbiting wholely in the Earth's shadow when crossing the night side of Earth).
I'd recommend John Naylor's "Out of the Blue" for many more wonderful aspects of the twilight sky. A harder to get book is Aden and Marjorie Meinel's "Sunsets, Twilights, and Evening Skies", which is considered one of the primary references on the subject.
atb,
John
  