Dark Sky Score
Combines moon phase, moon altitude, and Bortle class to predict astrophotography quality.
Inputs
Result
A natural placement between the calculator and the explanation.
What this solves — and what it doesn't
Three things make a dark sky: low moon, low light pollution, clear weather. Combine those with a long night (which latitude and season affect) and you have a milky-way window. This tool combines moon phase (computed from a synodic reference), Bortle (your sky darkness class), cloud cover, and latitude night length into a 0 to 100 score.
How to read the result
Read the score band:
- 80+ Excellent — go shoot the Milky Way
- 60 to 80 Good — wide-field astrophotography viable
- 40 to 60 Mediocre — moon interferes; lunar detail shots only
- <40 — skip or shoot planets/Moon only
Best milky-way windows are 3 days before/after new moon with Bortle ≤4.
Limitations
- Moon altitude not modeled — a full moon low on horizon is less bad than high.
- Bortle is user-estimated; a real measurement would help.
- No model of aurora activity (which overrides all else).
Frequently asked questions
How do I find my Bortle class?
Use a light-pollution map (lightpollutionmap.info). Most US east-coast suburbs are Bortle 5 to 7; national park backcountry is 1 to 3.
What about the Milky Way galactic core?
Best April to September in northern hemisphere, peaking in July. Plan around new moon in those months.
Is moon always bad?
No — a thin crescent is fine; the Milky Way is still visible. Full moon is the only real problem.