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(emacs)Sunrise/Sunset

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Times of Sunrise and Sunset
===========================

   Special calendar commands can tell you, to within a minute or two,
the times of sunrise and sunset for any date.

`S'
     Display times of sunrise and sunset for the selected date
     (`calendar-sunrise-sunset').

`Mouse-2 Sunrise/sunset'
     Display times of sunrise and sunset for the date you click on.

`M-x sunrise-sunset'
     Display times of sunrise and sunset for today's date.

`C-u M-x sunrise-sunset'
     Display times of sunrise and sunset for a specified date.

   Within the calendar, to display the _local times_ of sunrise and
sunset in the echo area, move point to the date you want, and type `S'.
Alternatively, click `Mouse-2' on the date, then choose
`Sunrise/sunset' from the menu that appears.  The command `M-x
sunrise-sunset' is available outside the calendar to display this
information for today's date or a specified date.  To specify a date
other than today, use `C-u M-x sunrise-sunset', which prompts for the
year, month, and day.

   You can display the times of sunrise and sunset for any location and
any date with `C-u C-u M-x sunrise-sunset'.  This asks you for a
longitude, latitude, number of minutes difference from Coordinated
Universal Time, and date, and then tells you the times of sunrise and
sunset for that location on that date.

   Because the times of sunrise and sunset depend on the location on
earth, you need to tell Emacs your latitude, longitude, and location
name before using these commands.  Here is an example of what to set:

     (setq calendar-latitude 40.1)
     (setq calendar-longitude -88.2)
     (setq calendar-location-name "Urbana, IL")

Use one decimal place in the values of `calendar-latitude' and
`calendar-longitude'.

   Your time zone also affects the local time of sunrise and sunset.
Emacs usually gets time zone information from the operating system, but
if these values are not what you want (or if the operating system does
not supply them), you must set them yourself.  Here is an example:

     (setq calendar-time-zone -360)
     (setq calendar-standard-time-zone-name "CST")
     (setq calendar-daylight-time-zone-name "CDT")

The value of `calendar-time-zone' is the number of minutes difference
between your local standard time and Coordinated Universal Time
(Greenwich time).  The values of `calendar-standard-time-zone-name' and
`calendar-daylight-time-zone-name' are the abbreviations used in your
time zone.  Emacs displays the times of sunrise and sunset _corrected
for daylight savings time_.  Note: Daylight Savings, for how daylight
savings time is determined.

   As a user, you might find it convenient to set the calendar location
variables for your usual physical location in your `.emacs' file.  And
when you install Emacs on a machine, you can create a `default.el' file
which sets them properly for the typical location of most users of that
machine.  Note: Init File.