[Kstars-devel] kdeedu/kstars/kstars

[Jason Harris]

CVS commit by harris: 

Fixing last portion of compound BR #71520.  The reporter found that the 
WUT tool did not report that the Moon and Venus were up on the night of 26 
Dec. 2003.  He provided photographic evidence that they were, in fact, 
visible that night :)

The problem was in our definition of what to consider "up" on a given 
night.  Naively, one might just consider whether the object is above the 
horizon at any time between sunset and sunrise.  However, what we really 
want to know is, can one *observe* a given object from a given location, 
on a given night?  In this case, we want to know if the object is above 
the horizon between the end of evening twilight and the beginning of 
morning twilight, not the moments of sunset and sunrise. 

Twilight is defined to end or begin when the Sun is at a certain negative 
altitude below the horizon.  There are three kinds of twilight: civil 
twilight (alt=-6 deg), nautical twilight (alt=-12 deg) and astronomical 
twilight (alt=-18 deg).  In KStars, we had been using -20 degrees, which 
is close to astronomical twilight.  

However, this is probably too strict, especially for planets and the moon 
which are often easily visible low in the sky during twilight.  We are now 
using the definition of civil twilight, -6 degrees, to determine whether 
an object is visible.

Wow, four paragraphs to explain a one-line change in the code.  :)  Sorry 
abot that!

CCMAIL: 71520 at bugs.kde.org
CCMAIL: kstars-devel at kde.org

 


  M +1 -1      wutdialog.cpp   1.21


--- kdeedu/kstars/kstars/wutdialog.cpp  #1.20:1.21
@@ -261,5 +261,5 @@ void WUTDialog::slotLoadList(int i) {
 bool WUTDialog::checkVisibility(SkyObjectName *oname) {
         bool visible( false );
-        double minAlt = 20.0; //minimum altitude for object to be considered 'visible'
+        double minAlt = 6.0; //An object is considered 'visible' if it is above horizon during civil twilight.
 
         //Initial values for T1, T2 assume all night option of EveningMorningBox