What Is the Bortle Scale? Understanding Light Pollution for Satellite Watching

The Bortle scale is a nine-level numeric scale that measures the night sky’s brightness (or darkness) at a given location. It directly affects how many satellites you can see and how dramatic they appear against the sky background.

The Bortle Scale Explained

Created by amateur astronomer John Bortle in 2001, the scale ranges from Class 1 (the darkest skies on Earth) to Class 9 (inner-city skies). Here’s what each level means for satellite watching:

Class 1 — Excellent Dark Sky

Zodiacal light, gegenschein, and zodiacal band all visible
The Milky Way casts shadows on the ground
Satellite watching: Spectacular. You’ll see dozens of satellites per hour, including very faint ones. The sky is so dark that satellites are visible almost to the horizon.
Found in: Remote wilderness areas, desert sites, mountain observatories

Class 2 — Typical Dark Sky

Milky Way is highly structured and detailed
Airglow (faint atmospheric luminescence) may be visible
Satellite watching: Excellent. Nearly as many satellites visible as Class 1. Faint tumbling rocket bodies and small debris become visible.
Found in: National parks, rural areas far from cities

Class 3 — Rural Sky

Milky Way still appears complex with dark lanes
Some light pollution visible low on the horizon
Satellite watching: Very good. Most satellites visible to the naked eye can be seen. A slight sky glow near the horizon may hide the faintest low-elevation passes.
Found in: Small rural communities, farmland

Class 4 — Rural/Suburban Transition

Milky Way visible but lacks detail
Light pollution domes visible in several directions
Satellite watching: Good. Bright and moderate satellites easily visible. Some fainter satellites lost in the sky glow, especially near the horizon.
Found in: Outer suburbs, small towns

Class 5 — Suburban Sky

Milky Way is faint and washed out
Only the brightest parts of the Milky Way visible overhead
Satellite watching: Moderate. The ISS and bright satellites are still spectacular. Dimmer satellites (magnitude +4 and fainter) become difficult. You’ll see roughly half the satellites visible from a dark site.
Found in: Typical suburbs

Class 6 — Bright Suburban Sky

Milky Way only visible near the zenith (straight up)
Sky background is noticeably gray, not black
Satellite watching: Fair. The ISS, Starlink trains, and bright satellites are still easy to see. Many dimmer satellites are invisible. Higher-elevation passes work best since the satellite is brighter and the sky is darkest overhead.
Found in: Suburbs of major cities

Class 7 — Suburban/Urban Transition

Milky Way essentially invisible
The entire sky has a grayish-white background
Satellite watching: Limited. Only the brightest satellites (ISS, Chinese Space Station, fresh Starlink trains) are easily visible. Focus on 3-star passes and high-elevation events.
Found in: City outskirts, dense suburbs

Class 8 — City Sky

Sky glows white or orange-gray
Only the brightest stars visible
Satellite watching: Poor for most satellites, but the ISS is still easily spotted during good passes. Its extreme brightness (up to magnitude -4) cuts through urban light pollution. Starlink trains within a day or two of launch are also visible.
Found in: Cities, commercial areas

Class 9 — Inner-City Sky

Only the Moon, planets, and a handful of stars visible
The sky is bright enough to read by
Satellite watching: Only the ISS during close, high-elevation passes. Even then, it may appear dimmer than expected against the bright sky background.
Found in: City centers, downtown areas, Times Square

How Bortle Class Affects What You See

Bortle Class	ISS	Bright Satellites	Dim Satellites	Starlink Trains
1–2	Dazzling	All visible	Most visible	Spectacular
3–4	Excellent	Most visible	Many visible	Great
5–6	Good	Easily visible	Some visible	Good
7–8	Visible	Brightest only	Very few	Recently launched only
9	Marginal	Very few	None	Unlikely

Finding Your Bortle Class

Every city page on LaunchSight shows the Bortle class for that location. You can also check your area:

Light pollution maps: Search for “light pollution map” — interactive maps show Bortle classes worldwide using satellite data
Your eyes: If you can see the Milky Way, you’re at Class 4 or darker. If you can count more than ~20 stars overhead, you’re likely Class 5 or better
LaunchSight city pages: Each of our city pages includes the estimated Bortle class

Improving Your Viewing Conditions

Even if you live in a Bortle 7–8 area, you can improve your experience:

Without Driving

Look straight up: The sky is always darkest at the zenith. Focus on high-elevation passes
Block local lights: Position yourself so buildings or trees block nearby streetlights
Time it right: The darkest period is typically 1–2 hours after sunset and before astronomical dawn
Focus on the ISS: It’s bright enough to see from anywhere

Short Drive (30–60 minutes)

Most cities are surrounded by Bortle 4–5 areas within a 30–60 minute drive
Even one Bortle class improvement makes a noticeable difference
State parks, reservoirs, and agricultural areas are reliable dark spots
Higher elevation helps — even a small hill reduces the effect of distant city lights

Dark Sky Parks

The International Dark-Sky Association certifies locations with exceptional night sky quality. Some notable US examples:

Cherry Springs State Park (PA) — Bortle 2
Big Bend National Park (TX) — Bortle 1–2
Natural Bridges National Monument (UT) — Bortle 2
Death Valley National Park (CA) — Bortle 1–2
Headlands International Dark Sky Park (MI) — Bortle 3

The Good News

The ISS — the most popular satellite to watch — is bright enough to see from any Bortle class. You don’t need dark skies to enjoy the most spectacular passes. Starlink trains within a few days of launch are also visible from cities.

For the full satellite watching experience with dozens of visible objects per evening, a trip to Bortle 3–4 skies is worth the drive. But you can start from your backyard tonight.

Check the Tonight tool for passes from your location, regardless of your Bortle class.