Bortle Scale

The Bortle scale rates night sky darkness from 1 (pristine) to 9 (inner-city). It was created by amateur astronomer John Bortle in 2001 and is the standard reference for astrophotography site selection.

Bortle 1-2: Excellent dark sky. The Milky Way casts visible shadows. Zodiacal light extends to the zenith. These sites are remote — think national parks far from cities. Ideal for deep-sky widefield astrophotography.

Bortle 3-4: Good dark sky. The Milky Way is clearly structured with dark lanes visible. Some light domes on the horizon from distant towns. Most dedicated astrophotography is done at Bortle 3-4 — accessible yet dark enough for serious work.

Bortle 5-6: Suburban sky. The Milky Way is visible but washed out. Light pollution is obvious in all directions. Short focal length nightscape shots are still possible, but long exposures show significant sky glow. A light pollution filter helps.

Bortle 7-9: Urban sky. Only bright stars and planets are visible. The Milky Way is invisible at Bortle 7+ and the sky never gets truly dark. Astrophotography is limited to the moon, planets, and very bright nebulae with narrowband filters.

For Fuji nightscape shooters: at Bortle 4 or darker, an f/1.4 prime on a star tracker produces stunning results. At Bortle 5-6, a light pollution filter and stacking multiple exposures compensates for the brighter sky. At Bortle 7+, consider driving to a darker site.