Use the chart below with the Light Pollution maps to guage the quality of your night skies where you live.
The column labeled "Naked-eye Limiting Magnitude" indicates the dimmest stars visible under each class of light pollution. The larger the magnitude number is, the dimmer the star is. Each whole number represents a factor of 2.51 in brightness. In other words, a magnitude 5 star appears approximately two and one-half times brighter than a magnitude 6 star, while a magnitude 4 star appears approximately five times brighter than a magnitude 6 star.
| Class | Color Key | Naked-eye Limiting Magnitude | Sky Description | Milky Way | Astronomical Objects | Zodiacal Light / Constellations | Airglow and Clouds | Night Time Scene |
|---|---|---|---|---|---|---|---|---|
| 1 | 7.6 - 8.0 | Excellent, truly dark-skies. | MW shows great detail and light from the Scorpio / Sagittarius region casts obvious shadows on the ground. | M33 (the Triangulum Galaxy) is an obvious object. | Zodiacal light has an obvious color and can stretch across the entire sky. | Bluish airglow is visible near the horizon and clouds appear as dark blobs againt the backdrop of the stars. | The brightness of Jupiter and Venus is annoying to night vision. Ground objects are barely lit and trees and hills are dark. | |
| 2 | 7.1 - 7.5 | Typical, truly dark skies. | Summer MW shouws great detail and has veined appearance. | M33 is visible with direct vision, as are many globular clusters. | Zodiacal light bright enough to cast weak shadows after dusk and has an apparent color. | Airglow may be weakly apparent and clouds still appear as dark blobs. | Ground is mostly dark, but objects projecting into the sky are discernible. | |
| 3 | 6.6 - 7.0 | Rural sky. | MW still appears complex, dark voids and bright patches and meandering outline are all visible. | Brightest Globular Clusters are distinct, but M33 is only visible with averted vision. M31 (the Andromeda Galaxy) is obviously visible. | Zodical light is striking in Spring and Autumn, extending 60 degrees above the horizon. | Airglow is not visible and clouds are faintly illuminated, except at the zenith. | Some light pollution eveidnet along the horizon. Ground objects are vaguely apparent. | |
| 4 | 6.1 - 6.5 | Rural / suburban transition. | Only well above the horizon does the MW reveal any structure. Fine details are lost. | M33 is a difficult object, even with averted vision. M31 is still readily visible. | Zodiacal light is clearly evident, but extends less than 45 degrees after dusk. | Clouds are faintly illuminated except at the zenith. | Light pollution domes are obviouse in several directions. Sky is noticeably brighter than the terrain. | |
| 5 | 5.6 - 6.0 | Suburban sky. | MW appears washed out overhead and is lost completely near the horizon. | The oval of M31 is detectable, as is the glow in the Orion Nebula. | Only nints of zodiacal light in Spring and Autumn. | Clouds are noticibly brighter than the sky, even at the zenith. | Light pollution domes are obviouse to casual observers. Ground objects are partly lit. | |
| 6 | 5.1 - 5.5 | Bright, suburban sky. | MW only apparent overhead and appears broken as fianter parts are lost to sky glow. | M31 is detectable only as a faint smudge; Orion Nebula is seldom glimpsed. | Zodiacal light is not visible. Constellations are seen and not lost against a starry sky. | Clouds anywhere in the sky appear fairly bright as they reflect back light. | Sky from horizon to 35 degrees glows with grayish color. Ground is well lit. | |
| 7 | 4.6 - 5.0 | Suburban / urban transition. | MW is totally invisible or nearly so. | M31 and the Beehive Cluster are rarely glimpsed. | The brighter constellations are easily recognizable. | Clouds are brilliantly lit. | Entire sky background appears washed out, with a grayish or yellowish color. | |
| 8 | 4.1 - 4.5 | City sky. | Not visible at all. | The Pleiades Cluster is visible, but very few other objects can be detected. | Dimmer constellations lack key stars. | Clouds are brilliantly lit. | Entire sky background has an orangish glow and it is bright enough to read at night. | |
| 9 | 4.0 at best | Inner city sky. | Not visible at all. | Only the Pleiades Cluster is visible to all but the most experienced observers. | Only the brightest constellations are discernable and they are missing stars. | Clouds are brilliantly lit. | Entire sky background has a broight glow, even at the zenith. |