Light pollution decides what you can photograph more than any piece of gear. A $400 smart telescope under a dark sky can beat a $4,000 rig downtown on the wrong target. The Bortle scale is the quickest way to describe your sky and set realistic goals.
What the Bortle scale is
Amateur astronomer John Bortle published the nine-step scale in Sky & Telescope in 2001. Class 1 is the darkest sky on Earth; class 9 is an inner-city sky. Each class is defined by what you can see with your eyes: how much of the Milky Way shows, how faint a star you can pick out (the naked-eye limiting magnitude), and how bright the horizon glows.
To find your class, use a light pollution map such as lightpollutionmap.info or check the sky yourself on a clear, moonless night after your eyes have adjusted for 20 minutes.
What each class looks like
| Bortle class | Typical place | Naked-eye limiting magnitude | Milky Way |
|---|---|---|---|
| 1 | Remote desert, ocean, high mountains | 7.6 to 8.0 | Casts faint shadows; zodiacal light obvious |
| 2 | Typical truly dark site | 7.1 to 7.5 | Highly structured, veined with dark lanes |
| 3 | Rural sky | 6.6 to 7.0 | Clearly structured; some glow on the horizon |
| 4 | Rural/suburban transition | 6.1 to 6.5 | Visible but lacking detail near the horizon |
| 5 | Suburbs | 5.6 to 6.0 | Washed out, faint overhead only |
| 6 | Bright suburbs | 5.1 to 5.5 | Barely visible at the zenith |
| 7 | Suburban/urban transition | 4.6 to 5.0 | Invisible |
| 8 | City | 4.1 to 4.5 | Invisible; sky glows gray or orange |
| 9 | Inner city | 4.0 or brighter | Invisible; only bright stars and planets |
AstroSight groups these into four settings: dark rural (1–3), suburbs (4–5), city edge (6–7) and inner city (8–9).
What you can shoot from each sky
Anywhere, including inner city
- The Moon. It is bright enough that light pollution makes no difference.
- The Sun, with a proper filter. See our solar photography safety guide.
- Planets. Jupiter, Saturn and Mars are bright, and planetary imaging uses very short exposures. Seeing (air steadiness) matters far more than darkness.
- Bright star clusters such as the Pleiades or the Double Cluster.
City and suburbs, with a narrowband filter
- Emission nebulae such as the Orion Nebula, the Lagoon, the Heart and Soul, and the North America Nebula. These glow at a few specific wavelengths, mainly hydrogen-alpha and oxygen-III. A narrowband filter passes those and blocks most of the streetlight glow around them.
Needs darker skies (Bortle 4 or darker, ideally 1–3)
- Galaxies. Their light is spread across the whole spectrum, just like light pollution, so no filter can separate them. Bright ones such as Andromeda and M81/M82 are possible from the suburbs with long integration times. Faint galaxies need dark skies.
- Reflection nebulae and dust, such as the Pleiades’ blue nebulosity or the dark nebulae around Rho Ophiuchi.
- The Milky Way and nightscapes. From Bortle 5 it is a faint band; from Bortle 7 it is gone. Plan a trip. See Milky Way with the camera you already own.
- Comets, whose faint tails vanish into bright skies.
Broadband, dual-band and narrowband filters
Broadband (light pollution reduction)
These block specific wavelengths from old sodium and mercury lamps. They helped a lot under orange sodium streetlights. Most cities now use broad-spectrum white LEDs, which these filters barely touch. They can help slightly with galaxies in mixed lighting, but do not expect much.
Dual-band
Dual-band filters pass narrow windows around hydrogen-alpha and oxygen-III and block almost everything else. The Optolong L-eNhance ($229, US list price as of September 2026; AstroSight shows the local price) is a popular example for one-shot color cameras. Several smart telescopes build one in, including the Dwarflab Dwarf 3, and the Dwarflab Draco has an Hα/OIII dual-narrowband filter.
Dual-band filters transform nebula imaging from a suburb or city. They do nothing useful for galaxies, star clusters or reflection nebulae, and they make stars look slightly odd in color.
Narrowband (single line)
Individual filters around 3 to 7 nm wide for hydrogen-alpha, oxygen-III and sulfur-II are used with monochrome cameras and a filter wheel. They cut light pollution and moonlight most aggressively and produce the “Hubble palette” look. This is the most effective way to image nebulae from Bortle 8 or 9, but it is also the most expensive and time-consuming route.
What this means for your gear
- Inner city: focus on the Moon, planets and narrowband nebulae. A Maksutov on a GoTo mount or a smart telescope with a dual-band filter makes sense.
- Suburbs: add bright galaxies and clusters with long integrations; nebulae with a dual-band filter.
- Dark rural: everything is open, including broadband galaxies and wide-field Milky Way.
The Moon also acts like temporary light pollution. Around full moon, even a Bortle 2 sky behaves like Bortle 6 or worse for broadband targets, while narrowband imaging carries on.
For hardware choices by sky, see the best smart telescopes of 2026 and why the mount matters in a first deep-sky rig. Or let AstroSight filter by your sky: nebulae, Moon and planets from the city edge.