DateAxis axis = (DateAxis) plot.getRangeAxis();
axis.setRange(_model.getStartDate(), _model.getEndDate());
axis.setLabel(_getXAxisLabel());
// mark the ranges of twilight and darkness
plot.clearRangeMarkers();
_addDarknessMarker(plot, _model.getNauticalTwilightStart(),
_model.getNauticalTwilightEnd(), TWILIGHT_ALPHA, Color.gray);
_addDarknessMarker(plot, _model.getAstronomicalTwilightStart(),
_model.getAstronomicalTwilightEnd(), DARKNESS_ALPHA, Color.black);