The sky is an endangered habitat.
Drag backthe night.
One measure of darkness. An entire universe of difference.
At class 9, the sky has become a luminous ceiling.
Use arrow keys for one Bortle class at a time. The entire page responds.
Night does not begin where the streetlight ends.
It begins when the pupil opens, nocturnal pollinators navigate, migrating birds see the horizon, and a child recognizes that the pale river overhead has always been home.
21 nights
below 0.20 mcd/m² in the 2029 sanctuary survey
What disappears first
The loss ledger
Light pollution does not erase the sky all at once. It takes it landmark by landmark, then removes the dark between them.
- 0912 stars
The sky itself
The background turns copper. Only a few major constellations keep their shape.
- 0842 stars
The dark between stars
Skyglow reaches the zenith. Newspaper headlines can be read without a lamp.
- 0790 stars
The Milky Way
Our galaxy vanishes entirely, even on moonless nights.
- 06180 stars
The winter clouds
Clouds glow brighter than the sky, reflecting the town below.
- 05360 stars
Structure in the galaxy
The Milky Way appears only as a weak, broken wash near the horizon.
- 04680 stars
The zodiacal light
The solar dust cone becomes difficult to separate from distant glow.
- 031,150 stars
Andromeda at a glance
Our neighboring galaxy returns as a small, steady oval without optics.
- 021,800 stars
Airglow and dust lanes
Dark rifts divide the Milky Way. The sky begins to show its own weather.
- 012,500+ stars
Depth
Stars cast faint shadows. The galaxy becomes architecture, not backdrop.
50% retrofit sky revealed
2029
Vesper turned down its lights. The galaxy came back.
The mountain town of Vesper replaced 1,184 exposed luminaires, set a 22:30 dimming curve, and capped blue-rich light. Three winters later, the zenith shifted from Bortle 6 to 3.
“We expected lower bills. We did not expect the mountains to gain a ceiling.”Leona Marr, night mayor of Vesper
- 74%
- less upward flux
- 2,900 K
- maximum street CCT
- 41%
- energy retained
Aim the light.
Keep the night.
Good lighting is not no lighting. It is warm, necessary, timed, and sent only where people need to see.
38% of emitted light escapes the task area.
62% useful light
glare + uplight
91% useful light
zero uplight
- 01Shield
No light above 90°.
- 02Warm
Keep sources at or below 2,900 K.
- 03Dim
Use the least light the task needs.
- 04Time
Curfew nonessential light at 22:30.
Preserve 21 field record
A sanctuary measured in absences.
No domes on the horizon. No permanent roadway. No unshielded source within the 312 km² core. What remains is wind, juniper, and 2,500 stars visible to an adapted eye.
Recalibrate the skyDarkness is not empty.
It is everything light lets us see.
Preserve 21 · Night habitat charter · Ratified 12 October 2029