Sky Visibility

1. Transparency

Lower is better.

SCORE & RATINGDESCRIPTION & VISUAL TEST
0.
Zero
Clouded out. Possible precipitation.
No stars visible.
1.
Very Poor.
Cloud covering most of sky.
Momentary patches of clear sky.
2.
Poor.
Patchy cloud or heavy haze.
Alpha and Beta Crux visible.
3.
Somewhat clear.
Cirrus or Moderate haze.
α, β, γ Crux visible.
4.
Partly clear.
Slight haze.
α, β, γ, δ Crux visible.
5.
Clear.
No clouds.
α, β, γ, δ, ε Crux visible.
6.
Very Clear.
No clouds, little sky glow, very little light pollution.
Milky way visible. All stars of Crux visible plus Coal Sack.
7.
Extremely Clear.
No clouds, minimal sky glow, Dark skies.
ω Centauri and 47 Tucanae visible to naked eye.

2. Seeing

Higher is better.

SCOREDESCRIPTION
1.Perfect, no movement of the image even at high magnification (100X plus).
2.Slight quiver with calm moments lasting several seconds.
3.Moderate quiver with larger tremors, blurring of image.
4.Poor constant undulation of image.
5.Very Bad not able to make even a rough sketch of image.

3. Bortle Scale

Higher is better.

TITLEDESCRIPTION & OBSERVATIONAL MAGNITUDE LIMIT
1.
Excellent
dark-sky site
Constellations may be barely recognizable amid the large number of stars.
Limiting magnitude with 12.5″ reflector is 17.5.
2.
Typical truly
dark site
Milky Way is highly structured.
Many Messier objects and globular clusters are naked-eye objects.
Limiting magnitude with 12.5″ reflector is 16.5.
3.
Rural
sky
Light pollution and clouds are evident at the horizon.
The Milky Way still appears complex.
Limiting magnitude with 12.5″ reflector is 16.
4.
Rural/
suburban
transition
Pollution domes visible in several directions.
The Milky Way is still impressive, but lacks detail.
Limiting magnitude with 12.5″ reflector is 15.5.
5.
Suburban
Sky
Light pollution is visible in most directions.
Clouds are noticeably brighter than the sky.
The Milky Way is very weak or invisible near the horizon
Limiting magnitude with 12.5″ reflector is 15.
6.
Bright
suburban
Sky
Light pollution makes the sky within 35° of the horizon glow gray.
White clouds anywhere in the sky appear fairly bright.
Background surroundings are easily visible.
The Milky Way is only visible near the zenith.
Limiting magnitude with 12.5″ reflector is 14.5.
7.
Suburban/
urban
transition
Sky
Light pollution makes the entire sky light grey. Clouds are bright.
Strong light sources are evident in all directions.
The Milky Way is nearly or totally invisible.
Limiting magnitude with 12.5″ reflector is 14.
8.
City
Sky
The sky is light gray or orange.
Stars forming familiar constellation patterns may be weak or invisible.
Limiting magnitude with 12.5″ reflector is 13.
9.
Inner-city
Sky
White.
Source of above information: Wikipedia