Military utility tools / First light and last light
First light and last light
Twilight, sunrise, sunset and moon data for any position and date. Everything computed here, nothing looked up.
Decimal degrees, north and east positive.
Set the inputs, then work it out.
BMNT--:--sun 12° below
First light--:--civil, 6° below
Sunrise--:--upper limb
Solar noon--:--sun due south
Sunset--:--upper limb
Last light--:--civil, 6° below
EENT--:--sun 12° below
Day length--sunrise to sunset
Usable light--first to last light
Moon--%—
Moonrise--:--± a few min
Moonset--:--± a few min
What is the difference between first light and BMNT?
BMNT is the beginning of morning nautical twilight, sun twelve degrees below the horizon. First light is normally the start of civil twilight at six degrees, when unaided work becomes possible. BMNT comes first.
How accurate is this?
About a minute for solar times and a few minutes for the moon. In practice terrain is a far larger source of error than the arithmetic.