01 · EARTH · THE LIGHT WE WASTE
Bortle Observatory
A 3D globe built on the 2025 light-pollution atlas. Tap anywhere on the planet to see its estimated Bortle class, the light domes on its horizon and what tonight will look like with today’s Moon.
THREE OBSERVATORIES · ONE SKY
Firmamento
BortleCero
THE MOON, TODAY
SIRIUS · 8.6 LIGHT-YEARS
01 — LIGHT
Everything you see in the sky
is light arriving late.
Bortle Cero follows light across three distances: the light we switch on down here that erases the sky, the light the Moon hands back from the Sun, and the light that left a star years ago and is only now arriving.
TIME FOR LIGHT TO REACH US · LOGARITHMIC SCALE
0 s
1.3 s
8 min 19 sThe Sun
8.6 years
-
0 s
The light we waste
A city’s glow doesn’t travel: it hangs in the air and wipes out the stars for hundreds of kilometres.
Bortle Observatory -
1.3 s
Borrowed light
The Moon doesn’t shine on its own: it reflects the Sun. That light crosses 384,400 km in just over a second.
Observatorio Lunar ES -
8.6 years
Light that travels
The light from Sirius you see tonight left more than eight years ago. Every star is a date.
El puente estelar
02 — THE SCALE
Bortle zero
doesn’t exist.
The Bortle scale rates the darkness of the night sky from 1 to 9. Class 1 is the darkest sky ever catalogued. Zero isn’t on the scale: it’s the sky we imagine, cleaner still. That’s where this project is looking.
SQM: zenith sky brightness in mag/arcsec². Conventional reference ranges. Between class 7 and 8 the sky stops being blue and turns sodium orange.
Assess your light footprint ES- 0The sky we imagineoff the scale
- 1Remote wilderness> 21.7
- 2Truly dark countryside21.1–21.7
- 3Rural area20.4–21.1
- 4Edge of town19.5–20.4
- 5Suburbs18.5–19.5
- 6Small city17.5–18.5
- 7City16.5–17.5
- 8Big city15.5–16.5
- 9Inner city< 15.5
03 — ORIGIN
It all began
with a photograph.
Bortle Cero grew out of Miguel’s nightscapes and his eclipse chasing: the Milky Way over the cardón cacti of Baja California, Earth’s shadow on the Moon, totality in Mazatlán in 2024. Every observatory in this sky started as a night in front of the camera.
Photographs by Miguel · Bortle Cero
MILKY WAY · PLAYA LA PERLA, BAHÍA CONCEPCIÓN, BAJA CALIFORNIA SUR · MAY 2025
Turn off a light.
Turn on the sky.
Three doors into the same sky. Pick your way in.