Calculate and plot the day-night terminator


gmt solar [ -B[p|s]parameters ] [ -C ] [ -Gfill|c ] [ -I[lon/lat][+ddate][+zTZ] ] [ -Jparameters ] [ -M ] [ -N ] [ -Q ] [ -Rregion ] [ -Tdcna[+ddate][+zTZ]] [ -U[stamp] ] [ -V[level] ] [ -Wpen ] [ -X[a|c|f|r][xshift[u]] ] [ -Y[a|c|f|r][yshift[u]] ] [ -bobinary ] [ -hheaders ] [ -oflags ] [ -pflags ] [ -ttransp ] [ --PAR=value ]

Note: No space is allowed between the option flag and the associated arguments.


solar Calculate and plot the day-night terminator and the civil, nautical and astronomical twilights.

Required Arguments


Optional Arguments

-B[p|s]parameters (more …)
Set map boundary frame and axes attributes.
Formats the report selected by -I using tab-separated fields on a single line. The output is Sun Lon Lat Azimuth Elevation in degrees, Sunrise Sunset Noon in decimal days, day length in minutes, SolarElevationCorrected corrected for the effect of refraction index and Equation of time in minutes. Note that if no position is provided in -Ilon/lat the data after Elevation refers to the point (0,0).
-Gfill|c (more …)
Select color or pattern for filling of terminators; or use -Gc for clipping [Default is no fill]. Deactivate clipping by appending the output of gmt clip -C.
Print current sun position as well as Azimuth and Elevation. Append lon/lat to print also the times of Sunrise, Sunset, Noon and length of the day. Add +ddate in ISO format, e.g, +d2000-04-25, to compute sun parameters for this date. If necessary, append time zone via +zTZ.
-Jparameters (more …)
Select map projection.
Write terminator(s) as a multisegment ASCII (or binary, see -bo) file to standard output. No plotting occurs.
Invert the sense of what is inside and outside the terminator. Only used with clipping (-Gc) and cannot be used together with -B.
-Rxmin/xmax/ymin/ymax[+r][+uunit] (more …)
Specify the region of interest.
Plot (or dump; see -M) one or more terminators defined via the dcna flags. Where: d means day/night terminator; c means civil twilight; n means nautical twilight; a means astronomical twilight. Add +ddate in ISO format, e.g, +d2000-04-25T12:15:00 to know where the day-night was at that date. If necessary, append time zone via +zTZ.
-U[label][+c][+jjust][+odx/dy] (more …)
Draw GMT time stamp logo on plot.
-V[level] (more …)
Select verbosity level [c].
-W[-|+][pen] (more …)
Set pen attributes for lines or the outline of symbols [Defaults: width = default, color = black, style = solid].


-Y[a|c|f|r][yshift[u]] (more …)
Shift plot origin.
-bo[ncols][type] (more …)
Select native binary output.
-h[i|o][n][+c][+d][+rremark][+rtitle] (more …)
Skip or produce header record(s).
-ocols[,…][t[word]] (more …)
Select output columns (0 is first column; t is trailing text, append word to write one word only).
-p[x|y|z]azim[/elev[/zlevel]][+wlon0/lat0[/z0]][+vx0/y0] (more …)
Select perspective view.
-t[transp] (more …)
Set PDF transparency level in percent.


Print current Sun position and Sunrise, Sunset times at:

gmt solar -I-7.93/37.079+d2016-02-04T10:01:00

Plot the day-night and civil twilight

gmt begin
gmt coast -Rd -W0.1p -JQ0/14c -Ba -BWSen -Dl -A1000
gmt solar -W1p -Tdc
gmt end

Set up a clip path overlay based on the day/night terminator:

gmt solar -Gc -Tc


Code from the Excel Spreadsheets in


Taken from the NOOA site Data for Litigation note.

The NOAA Solar Calculator is for research and recreational use only. NOAA cannot certify or authenticate sunrise, sunset or solar position data. The U.S. Government does not collect observations of astronomical data, and due to atmospheric conditions our calculated results may vary significantly from actual observed values.

For further information, please see the U.S. Naval Observatory’s page Astronomical Data Used for Litigation

See Also

gmt, clip, coast, plot