How Moon Where computes its observing score
Read the astronomical and weather weights and their limits. A heuristic score is not a calibrated success probability.
A score is not a measured probability
The rules combine lunar altitude, solar altitude, illumination and cloud/rain forecasts. A score of 80 is not an 80% chance of success. The model has not been calibrated against a field-observation sample and does not measure your skyline or local fog.
The time-slot formula
The base score is round(astronomy × 0.55 + weather × 0.45). Astronomy comprises altitude up to 40 points, background contrast up to 35 and phase visibility up to 25. Altitude thresholds of 10°, 15°, 25° and 35° receive 18, 26, 34 and 40 points. Weather comprises cloud up to 60, rain up to 30 and a transparency baseline of 10; that baseline is not an on-site measurement.
Cloud thresholds at 15%, 30%, 50%, 70% and 85% receive 60, 50, 35, 18 and 6 points respectively; above 85% receives zero.
Caps and separate summaries
At cloud cover of at least 85%, the final score is capped at 20. Rain above 0.5mm or precipitation probability at least 75% caps it at 15; daylight glare caps it at 18. Below-horizon and very-low-altitude cases have early rules. Daily summary cards use separate aggregation and should not be compared as identical scales. Recommended windows favor sustained usable intervals.
Missing weather means uncertainty
When a forecast is unavailable, lunar coordinates remain calculable but cloud conditions are unknown. Check the sky rather than treating a calculated estimate as a confirmed sighting. Forecast cloud cover describes a grid, not a specific cloud crossing the Moon.
Purpose planner · Moon classroom · Observing places
Sources and review
Moon Where operator · Reviewed: 2026-10-07. AI assisted drafting; explanation reviewed against cited sources and application code. Hypothetical examples are identified.