BortleSlider
How dark the sky is where you are standing, on Bortle's 1—9 scale, wrapping a
<Slider> whose track is the sky it selects:
the gradient is the atmosphere shader's own ((bortle − 1) / 8)²
curve, so classes 1—4 stay genuinely dark and the damage visibly starts at 5.
The reading leads and the jargon follows. The control used to be labelled
BORTLE SCALE — a surname as the primary label —
with the only phrase a reader could act on demoted to a caption. It renders inline;
on the map it is the first control in
SkyConditions.
Rural sky
Bortle 3 ·
The engine is not running here, so the handle moves and the naked-eye limit stays blank.