I'm on the 19th floor of One Canada Square in London
and that is a GORGEOUS sunset .
And soon the sun will dip below the horizon
and it will be twilight.
See, night doesn't technically start--
at least under formal definitions --
until the sun is 18° below the horizon.
And until then, there are three types of twilight:
First of all there is civil twilight,
that's when the sky is still fairly light and you can walk about without worrying you're going to trip over something,
that's 0° to 6° below the horizon.
Next up is nautical twilight,
that's when you can just about see the horizon against the sky if you're navigating on a boat,
that's 6° to 12°.
And finally there is astronomical twilight,
where it's still just a little bit too light
for the really faint objects like nebulae and galaxies
to come out in the sky,
that: 12° to 18°.
And then finally, when the sun tips under that,
then it formally becomes night.
But the thing is in midsummer,
when it's really really bright,
when it's the sun, high in the sky
the United Kingdom is north enough,
that it never becomes night,
that from evening to morning we are perpetually in twilight,
until finally Autumn rolls around and we dip into night once again.
America doesn't quite get it,
Vancouver in Canada just stretches into that definition,
but the whole of the UK,
and of course a lot of northern Europe,
well, we have entire seasons when we never ever technically have night.
That is twilight,
that is a really gorgeous sunset
and that is something you might not have known.
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