Evidence, calculations and limits
Sources and Methodology
The site combines authoritative source material, astronomical calculations, mapped context, and practical planning criteria. Each component answers a different question.
Selecting sources
Source choice begins with the claim. Park rules should come from the park or responsible authority. Road restrictions belong to road agencies or local government. Climate normals and weather records should come from meteorological institutions. Observatory access and visitor arrangements should come from the operator. Dark-sky recognition should be checked against the organization that issued it.
Recency matters most when a fact can change quickly. A road notice from several years ago may be unsuitable even if the geography is unchanged. By contrast, elevation, latitude, broad terrain, and long-term astronomical relationships usually remain stable.
Main evidence categories
Astronomical data
Latitude, longitude, solar position, twilight thresholds, Moon phase, Moonrise and Moonset, seasonal night length, and visibility windows.
Environmental data
Cloud patterns, precipitation, humidity, aerosols, wildfire smoke, dust, temperature, wind exposure, altitude, and horizon conditions.
Human environment
Population centers, artificial light, tourism pressure, traffic, settlement lighting, nearby industry, and temporary events.
Access and governance
Road status, public transport, ferry schedules, protected-area rules, land ownership, opening hours, permits, seasonal gates, and observatory policies.
Astronomical darkness
Full astronomical darkness is generally evaluated using the period when the Sun is at least 18 degrees below the horizon. At high latitudes this condition may be brief or absent during part of the year. A long winter night can offer extended darkness, while cloud, snow brightness, aurora activity, or extreme cold can still reduce practical observing value.
Calculated darkness is not the same as clear sky. It describes solar geometry for a location and date under defined assumptions.
Light-pollution context
Light-pollution maps and satellite-derived layers are useful for comparing broad patterns, city light domes, settlement corridors, and darker regional zones. They may not capture recent development, temporary lighting, snow reflection, local fixtures, horizon obstructions, atmospheric scattering, or a lamp close to the observer.
A mapped value is therefore treated as regional context. It is not converted automatically into a guaranteed on-site Bortle class or an SQM reading.
Weather and atmosphere
Long-term climate data can indicate whether a season tends to be cloudier, drier, windier, or more humid. It cannot forecast a particular night. Live decisions require current forecasts, satellite imagery where appropriate, warnings, road information, and observation of local conditions.
Transparency and seeing are also different. A visually clear sky may contain haze, dust, smoke, moisture, or high cloud that reduces faint-object contrast. Stable air can help planetary observation while a dry, transparent atmosphere may better support deep-sky viewing.
Map markers
Markers identify regional planning centers, recognized sites, public facilities, settlements, parks, observatory areas, or approximate geographic references. A marker does not establish legal parking, unrestricted entry, safe ground, public ownership, open gates, or permission to remain after dark.
Comparison methods
Country and location comparisons may combine darkness potential, cloud or transparency context, light escape, altitude, access, seasonal usability, and trip-specific value. Weights can differ when the page answers a different planning question. A desert photography comparison should not be assumed to use the same emphasis as an aurora-access comparison.
When exact measurement is unavailable, the method uses categories or bounded estimates rather than invented precision. Missing data is not silently treated as an ideal value.
Rounding and precision
Displayed values may be rounded for readability. Extra decimal places are avoided when the underlying evidence does not support that level of certainty. Small score differences should not be interpreted as proof that one destination will outperform another on a particular night.
Review dates
A review date indicates when the page or a substantial part of it was checked. External pages, regulations, schedules, designations, and road conditions may change later. Readers should open the responsible authority’s current information before travel.