.TH BLUE 1 BLUE
.SH "NAME"
blue - Creates table of when the blue hour etc. occurs
.SH "SYNPOSIS"
.nf
\fBblue\fP [\fB-d\fP \fIdelev\fP]* [\fB-D\fP \fIdelev\fP]* [\fB-e\fP \fIelev\fP]* [\fB-m\fP \fIelev\fP]* [\fB-h\fP [\fB-L\fP] | \fB-u\fP | \fB-L\fP]
[\fB-l\fP \fIlat\fP\fB:\fP\fIlon\fP | \fB-l\fP \fIloc\fP] [\fB-s\fP \fIyear\fP\fB-\fP\fImonth\fP\fB-\fP\fIday\fP | \fB-s\fP \fB-\fP] [\fB-r\fP \fInum\fP[\fBh\fP|\fBm\fP|\fBs\fP]]
[\fB-bBgGnN\fP]
.fi
.SH "DESCRIPTION"
.B blue
prints a list of time point when the select event occurs.
.SH "OPTIONS"
.TP
.B \-b
List the time when the blue hour begins. (default)
.TP
.B \-B
List the time when the blue hour ends.
.TP
\fB\-d\fP \fIDELEV\fP
List the time when the first derivative of the Sun's elevation is
.I DELEV
and the Sun's elevation is non-negative (daytime).
.TP
\fB\-D\fP \fIDELEV\fP
List the time when the first derivative of the Sun's elevation is
.I DELEV
and the Sun's elevation is non-positive (nighttime).
.TP
\fB\-e\fP \fIELEV\fP
List the time when the Sun's elevation is
\I ELEV
and the first derivative of the Sun's elevation is
non-positive (evening).
.TP
.B \-g
List the time when the golden hour begins.
.TP
.B \-G
List the time when the golden hour ends.
.TP
.B \-h
Print times in human readable format.
.TP
\fB\-l\fP \fILATITUDE\P:\fILONGITUDE\fP
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.
.TP
\fB\-l\fP \fILOCATION\fP
Use a named location. In particular, the one stored in the
file
.RI ~/.config/geolocation.d/ LOCATION ,
or the file
.IR 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.
.TP
.B \-L
Print times in local time.
.TP
\fB-e\fP \fIELEV\fP
List the time when the Sun's elevation is
.I ELEV
and the firs derivative of the Sun's elevation is
non-negative (morning).
.TP
.B \-n
List the time of solar noon.
.TP
.B \-N
List the time of solar midnight.
.TP
\fB\-r\fP \fIRES\fP
Print the in
.I RES
resultion.
.I RES
must be an integer followed by on the the suffixes:
.nf
h hours
m minutes (min is not a valid suffix)
s seconds
.fi
For example:
.B \-r 15m
prints the nearest quarters of the times.
.TP
\fB\-s\fP \fIDATE\fP
The last date (local time) to include in the last.
.I DATE
must be in
.B %Y-%m-%d
(year dash month dash day) format.
A dash (-) for an infinite list. Default limit is one month.
.TP
.B \-u
Print times in UNIX-time format.
.SH "FILES"
.TP
.B ~/.config/geolocation
Used to get your location if
.B \-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.
.TP
.B /etc/geolocation
Fallback file use if ~/.config/geolocation is missing. Other
programs are encouraged to use this file too.
.TP
.B ~/.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.
.TP
.B /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.
.SH "RATIONALE"
This is useful if you plan to take nice photographies, for example
during the blue hours, or the golden hour.
.SH "NOTES"
US Americans, remember, you are on the Western Hemisphere.
Therefore, you should specify a negative longitude.
.SH "SEE ALSO"
.BR locateme (1)
