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lethargic_manIf you look at, for example the sunrise and sunset almanac on timeanddate.com, you'll see there are three types of twilight: civil twilight (taking the sun to 6° below the horizon), nautical twilight (to 12°) and astronomical twilight (18°).
Wikipedia explains: at civil dusk (the end of civil twilight), terrestrial objects may no longer in good weather conditions be clearly distinguished; at nautical dusk navigation via the horizon at sea is no longer possible; and whilst astronomical twilight might look like full night to the casual observer, there is still too much light to observe stars, nebulae or galaxies which are no brighter than sixth magnitude.
However, as a cyclist, and a (reasonably) observant Jew, the periods of twilight divide for me more naturally into: fifteen minutes of good lighting conditions (in the absence of overcast) for cycling, fifteen minutes of failing lighting conditions, and fifteen minutes of "Is Shabbos out yet?" :o)
Wikipedia explains: at civil dusk (the end of civil twilight), terrestrial objects may no longer in good weather conditions be clearly distinguished; at nautical dusk navigation via the horizon at sea is no longer possible; and whilst astronomical twilight might look like full night to the casual observer, there is still too much light to observe stars, nebulae or galaxies which are no brighter than sixth magnitude.
However, as a cyclist, and a (reasonably) observant Jew, the periods of twilight divide for me more naturally into: fifteen minutes of good lighting conditions (in the absence of overcast) for cycling, fifteen minutes of failing lighting conditions, and fifteen minutes of "Is Shabbos out yet?" :o)
