Moon Avoidance Calculator
Decision making for astrophotography based on the moon phase.
Observing Location
Used for moon altitude and astronomical twilight (dusk/dawn)
calculations. Saved in your browser for next time.
Session Input
:
Times are evaluated in your browser's local timezone. Separation
between object and moon changes only slowly over a night, so one
time near mid-session is enough. Dusk/Dawn presets compute
astronomical twilight (sun at −18°) for the selected date and
roll the date forward automatically when past midnight.
Readout
Moon RA / Dec
—
Target RA / Dec
—
Angular Separation
—
Recommended Minimum
—
0°180°
—
Enter a target, filter, and date above.
Threshold reference table
| Filter | 0% (new) | 50% (qtr) | 100% (full) |
|---|---|---|---|
| SII | 15° | 22° | 30° |
| Hα | 20° | 30° | 40° |
| OIII | 25° | 42° | 60° |
| Luminance | 35° | 62° | 90° |
| RGB | 45° | 82° | 120° |
Narrowband (Hα/SII) rejects most moonlight by bandpass alone
— tolerable close to a gibbous or full moon. OIII picks up
more scatter (moonlight carries blue-green content).
Broadband L/RGB is most vulnerable, and at a Bortle 6–7 site
the moon adds directly on top of an already-elevated
background — prioritize narrowband during moon-heavy weeks,
save RGB/L for dark-of-moon. These are heuristic starting
points, not hard physics — tighten or loosen them against
your own gradient/background results over time. If moon
altitude is below 0°, it isn't a factor regardless of
separation.