Visibility
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The visibility curve shows the altitude of all sources visible
between the start of the astronomical twilight in the evening and the
end of the astronomical twilight in the morning. It only shows sources visibly above
65&deg; zenith distance.

The title shows roughly the start and end time of the time range diaplayed
and the number of  minutes corresponding to one of the twenty
steps on the x-axis.

To relate the curves to the visible sources, the order in which they
culminate is given above the graphics. For sources culminating within
the displayed time-range, also their zenith distance at culmination is
listed. 

Note that the zenith distance is counted from the zenith, while
the altitude is counted from the horizon: Zd=90&deg;-Alt  
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