planetarium/: Tweak manual.

diff --git a/src/planetarium/mit-scheme-planetarium.texi b/src/planetarium/mit-scheme-planetarium.texi
index 91a554eadd85829e6c13aff68152ff4f674e2575..70ee5eb3363b7e722bf9c3f356f3e20e1b265e03 100644 (file)
--- a/src/planetarium/mit-scheme-planetarium.texi
+++ b/src/planetarium/mit-scheme-planetarium.texi
@@ -57,7 +57,7 @@ position of the sun by drawing a face of Earth and shading its dark
 side.  If an old X11 graphics device is all that is available, just
 the terminator is drawn.
 
-To use, startup mit-scheme and enter these following two s-expressions
+To use, startup mit-scheme and enter the following two s-expressions
 at the REPL prompt.
 
 @example
@@ -72,8 +72,9 @@ Returns a new tellurion, a closure to which messages can be sent.
 @end deffn
 
 You can send a @code{turn-to} message to the tellurion, specifying a
-latitude and longitude in degrees, by applying it to three arguments:
-the symbol @code{turn-to} and the latitude and longitude (numbers).
+latitude and longitude to place in the center of the drawing.  To send
+the message, apply the tellurion to three arguments: the symbol
+@code{turn-to} and the latitude and longitude in degrees.
 
 For example, to center the globe on Fairbanks, Alaska, enter this:
 @example
@@ -81,9 +82,11 @@ For example, to center the globe on Fairbanks, Alaska, enter this:
 @end example
 
 You can also have the tellurion draw the terminator as it would appear
-at a particular time (other than the current time).  Apply it to the symbol
-@code{time-to} and a time, either a decoded time or an integer to be
-interpreted as a universal time.
+at a particular time.  Apply it to the
+symbol @code{time-to} and a time, either a decoded time or a universal
+time (an integer).  (See the reference manual's section ``Date and
+Time''.)
+
 @example
     (t 'TIME-TO (make-decoded-time 0 29 9 19 3 2016)) ;; a vernal equinox
 @end example