The Observer's Nights within the interval: every span in
which the Sun is below nightSunAltitude, 6 degrees below the horizon
unless the caller says otherwise (NIGHT_SUN_ALTITUDE), cut to the
interval, in time order. Each edge is taken on its Twilight side, so
every instant of Night is inside one.
The Sun's altitude is walked with a step it cannot cross Night's edge
within, from how far it is from it and how fast it can move, so a Night
is never stepped over: a long stride through the middle of the day and
of the night, short ones only at dusk and dawn. A Night shorter than a
second, where the Sun only grazes the edge, can be stepped over, as a
Pass that short can. None where the Sun never sets that far, as in a
summer far north; the whole interval where it never rises that far.
The Observer's Nights within the interval: every span in which the Sun is below
nightSunAltitude, 6 degrees below the horizon unless the caller says otherwise (NIGHT_SUN_ALTITUDE), cut to the interval, in time order. Each edge is taken on its Twilight side, so every instant of Night is inside one.The Sun's altitude is walked with a step it cannot cross Night's edge within, from how far it is from it and how fast it can move, so a Night is never stepped over: a long stride through the middle of the day and of the night, short ones only at dusk and dawn. A Night shorter than a second, where the Sun only grazes the edge, can be stepped over, as a Pass that short can. None where the Sun never sets that far, as in a summer far north; the whole interval where it never rises that far.