NAME
	blue - Creates table of when the blue hour etc. occurs

SYNPOSIS
	blue [-d delev]* [-D delev]* [-e elev]* [-m elev]* [-h [-L] | -u | -L]
	     [-l lat:lon | -l loc] [-s year-month-day | -s -] [-r num[h|m|s]]
	     [-bBgGnN]

DESCRIPTION
	blue prints a list of time point when the select event occurs.

OPTIONS
	-b
		List the time when the blue hour begins. (default)

	-B
		List the time when the blue hour ends.

	-d DELEV
		List the time when the first derivative of the Sun's elevation
		is DELEV and the Sun's elevation is non-negative (daytime).

	-D DELEV
		List the time when the first derivative of the Sun's elevation
		is DELEV and the Sun's elevation is non-positive (nighttime).

	-e ELEV
		List the time when the Sun's elevation is ELEV and the first
		derivative of the Sun's elevation is non-positive (evening).

	-g
		List the time when the golden hour begins.

	-G
		List the time when the golden hour ends.

	-h
		Print times in human readable format.

	-l LATITUDE:LONGITUDE
		Tell blue where you are. The values are measured in degrees
		and in the GPS (you probably do not have too care about that,
		the differences between the systems should not be significant
		another), and must be in decimal.

		Reminder for Americans (particularly US Americans), you are
		an the western hemisphere, not the eastern, thus your longtiude
		is negative. If you experience weird time listings, 100 % of
		the times it is because you forgot the minus sign. But no need
		to feel stupid, it is a really common mistake.

		No complicated stuff please, only latitudes within ±90° and
		longitudes within ±180°. No unit thought.

	-l LOCATION
		Use a named location. In particular, the one stored in the
		file ~/.config/geolocation.d/LOCATION, or the file LOCATION,
		if it begins with either ./ (dot slash), ../ (dot dot slash),
		or / (slash). By default ~/.config/geolocation, or
		/etc/geolocation as a fallback, is used.

	-L
		Print times in local time.

	-e ELEV
		List the time when the Sun's elevation is ELEV and the first
		derivative of the Sun's elevation is non-negative (morning).

	-n
		List the time of solar noon.

	-N
		List the time of solar midnight.

	-r RES
		Print the in RES resultion. RES must be an integer followed
		by on the the suffixes:

		h  hours
		m  minutes (min is not a valid suffix)
		s  seconds

		For example: -r 15m prints the nearest quarters of the times.

	-s DATE
		The last date (local time) to include in the last. DATE must
		be in %Y-%m-%d (year dash month dash day) format. A dash (-)
		for an infinite list. Default limit is one month.

	-u
		Print times in UNIX-time format.

FILES
	~/.config/geolocation
		Used to get your location if -l is not used. This file contains
		your geographical location using the Global Positioning System
		in decimal format. This will never change. Other programs are
		encouraged to use this file too.

		If the file contains more than one line, only the first line,
		even if it is empty, is used.

	/etc/geolocation
		Fallback file use if ~/.config/geolocation is missing. Other
		programs are encouraged to use this file too.

	~/.config/geolocation.d/
		Directory used for named locations. The files are formatted
		in the same way as ~/.config/geolocation. Other programs are
		encouraged to use this directory too.

	/etc/geolocation.d/
		Directory used for named locations, used when the named
		location is not listed in ~/.config/geolocation.d/. The files
		are formatted in the same way as ~/.config/geolocation. Other
		programs are encouraged to use this directory too.

RATIONALE
	This is useful if you plan to take nice photographies, for example
	during the blue hours, or the golden hour.

NOTES
	US Americans, remember, you are on the Western Hemisphere. Therefore,
	you should specify a negative longitude.

SEE ALSO
	locateme(1)