source: buchla-68k/orig/DATE/SUNNOTES.txt@ 0170798

From: ihnp4!tektronix!reed!nsc-pdc!rgb
Date: Tue, 28 May 85 09:08:58 pdt
Subject: Re:  sun(1)

The best book I have seen to date is a small book called "Practical
Astronomy With Your Calculator" by Peter(?) Duffet-Smith.  I was able
to order a copy from a local bookstore.  The B. Dalton here said they
stock it, but they happened to have sold them all.

As far as the definition of sunset, there are lots of them. The program
uses the time when the upper limb of the sun descends below the horizon.
Note that it is calculated for the observer; a more accurate calculation
would include your mountains. Refraction causes a sun which is already
below the horizon to appear to be above.  

The program calculates some corrections for sunset and sunrise positions
based on the refraction of the air, parallax, and one other thing I
forget now.  The postion figures don't do the correction: I wimped out
because the refraction correction is a function of the height of the
sun above the horizon.  The sunrise and sunset are apparent times, 
you should remove the dt correction to find the "astronomical" times.
Try the first day of spring at dawn to see what I mean.  The sun should
come up almost exactly in the east, but it's apparent position is
different because of the corrections.

I hope this is understandable...

                                                Bob Bond
* Each option yields one type of output line, more or less.
* Set time in a variety of ways, including just hour or hour:min.
* Ditto for date.
* Option to get current or specified time included.
* Option to get just current position.
* Option to get time since/until previous/next sunrise/set, and percent of
  interval elapsed/remaining.
* Option to get length of day/night and percents.
* Work with standard TZ information.

Input options:

-a      latitude
-o      longitude
-z      timezone
[date and time] only argument allowed, various formats

Output options, sample:

-P      Latitude, longitude:     40.02N 105.43W
-d      Date, time:             850419   10:33  (MDT)
-t(def) Rise, set times:          5:33   20:19  (MDT)
-a      Rise, set azimuth:       61 19' 298 51'
-p      Current elev, azimuth:   38 14' 180 00'
-s      Since-/till+ rise, set:  -4:44  +10:02
-S      Since-/till+ rise, set: -31.3%  +68.7%
-l      Length of night, day:    14:10    9:50
-L      Length of night, day:    60.2%   39.8%

-f      full, all of above