{"assessment":{"best_window":{"end":"2026-05-21T21:00Z","end_local":"00:00","hours":1.33,"label":"marginal","mean_quality":0.4,"start":"2026-05-21T19:40Z","start_local":"22:40"},"cost":{"altitude":0.0,"clouds":4.95,"darkness":3.13,"moon":0.58},"formula":"astronomy = 100 * min(1, sky_hours / reference_hours) * peak_sky; overall = astronomy * score_weather / 100 (null when the weather is unknown)","hard_limit":null,"headline":"Barely","hourly":[{"alt":null,"cloud":69,"high":59,"iso":"2026-05-21T18:00Z","label":"unusable","low":9,"mid":25,"moon_alt":48,"precip":0.0,"q":0.0,"rh":92,"sky":"civil twilight","temp":6.4,"time":"21:00","wind":12.0},{"alt":null,"cloud":47,"high":30,"iso":"2026-05-21T19:00Z","label":"poor","low":13,"mid":15,"moon_alt":37,"precip":0.0,"q":0.19,"rh":92,"sky":"astronomical twilight","temp":6.0,"time":"22:00","wind":11.0},{"alt":null,"cloud":46,"high":18,"iso":"2026-05-21T20:00Z","label":"marginal","low":16,"mid":23,"moon_alt":26,"precip":0.0,"q":0.39,"rh":94,"sky":"night","temp":5.5,"time":"23:00","wind":10.7},{"alt":null,"cloud":89,"high":8,"iso":"2026-05-21T21:00Z","label":"unusable","low":23,"mid":85,"moon_alt":15,"precip":0.0,"q":0.0,"rh":95,"sky":"night","temp":5.4,"time":"00:00","wind":10.0},{"alt":null,"cloud":88,"high":12,"iso":"2026-05-21T22:00Z","label":"unusable","low":7,"mid":86,"moon_alt":5,"precip":0.0,"q":0.0,"rh":93,"sky":"night","temp":6.0,"time":"01:00","wind":10.3},{"alt":null,"cloud":80,"high":1,"iso":"2026-05-21T23:00Z","label":"unusable","low":13,"mid":77,"moon_alt":-5,"precip":0.0,"q":0.0,"rh":94,"sky":"night","temp":5.9,"time":"02:00","wind":10.0},{"alt":null,"cloud":95,"high":0,"iso":"2026-05-22T00:00Z","label":"unusable","low":77,"mid":80,"moon_alt":-14,"precip":0.0,"q":0.0,"rh":97,"sky":"night","temp":6.2,"time":"03:00","wind":11.3},{"alt":null,"cloud":74,"high":25,"iso":"2026-05-22T01:00Z","label":"poor","low":58,"mid":19,"moon_alt":-22,"precip":0.0,"q":0.09,"rh":97,"sky":"astronomical twilight","temp":6.0,"time":"04:00","wind":10.3},{"alt":null,"cloud":94,"high":41,"iso":"2026-05-22T02:00Z","label":"unusable","low":90,"mid":2,"moon_alt":-27,"precip":0.0,"q":0.0,"rh":98,"sky":"nautical twilight","temp":5.3,"time":"05:00","wind":10.8}],"peak_quality":0.41,"peak_sky":1.0,"quality_hours":0.75,"reasons":["cloud cover cost 5.0 quality-hours","daylight and twilight cost 3.1 quality-hours","moonlight cost 0.6 quality-hours"],"reference_hours":4.0,"score":13,"score_astronomy":100,"score_weather":13,"sky_hours":5.71,"verdict":"poor","verdict_astronomy":"good","weather_known":true,"windows":[{"end":"2026-05-21T18:15Z","end_local":"21:15","hours":0.67,"label":"unusable","mean_quality":0.0,"start":"2026-05-21T17:35Z","start_local":"20:35"},{"end":"2026-05-21T19:40Z","end_local":"22:40","hours":1.42,"label":"poor","mean_quality":0.11,"start":"2026-05-21T18:15Z","start_local":"21:15"},{"end":"2026-05-21T21:00Z","end_local":"00:00","hours":1.33,"label":"marginal","mean_quality":0.4,"start":"2026-05-21T19:40Z","start_local":"22:40"},{"end":"2026-05-22T01:00Z","end_local":"04:00","hours":4.0,"label":"unusable","mean_quality":0.0,"start":"2026-05-21T21:00Z","start_local":"00:00"},{"end":"2026-05-22T02:00Z","end_local":"05:00","hours":1.0,"label":"poor","mean_quality":0.07,"start":"2026-05-22T01:00Z","start_local":"04:00"},{"end":"2026-05-22T03:00Z","end_local":"06:00","hours":1.0,"label":"unusable","mean_quality":0.0,"start":"2026-05-22T02:00Z","start_local":"05:00"}]},"calculation_version":"2026-10-10.1","forecast":[{"cloud":21,"dark":false,"high":20,"local":"20:00","low":1,"mid":2,"precip":0.0,"rh":87,"temp":7.9,"time":"2026-05-21T17:00Z","wind":14.0},{"cloud":69,"dark":false,"high":59,"local":"21:00","low":9,"mid":25,"precip":0.0,"rh":92,"temp":6.4,"time":"2026-05-21T18:00Z","wind":12.0},{"cloud":47,"dark":false,"high":30,"local":"22:00","low":13,"mid":15,"precip":0.0,"rh":92,"temp":6.0,"time":"2026-05-21T19:00Z","wind":11.0},{"cloud":46,"dark":true,"high":18,"local":"23:00","low":16,"mid":23,"precip":0.0,"rh":94,"temp":5.5,"time":"2026-05-21T20:00Z","wind":10.7},{"cloud":89,"dark":true,"high":8,"local":"00:00","low":23,"mid":85,"precip":0.0,"rh":95,"temp":5.4,"time":"2026-05-21T21:00Z","wind":10.0},{"cloud":88,"dark":true,"high":12,"local":"01:00","low":7,"mid":86,"precip":0.0,"rh":93,"temp":6.0,"time":"2026-05-21T22:00Z","wind":10.3},{"cloud":80,"dark":true,"high":1,"local":"02:00","low":13,"mid":77,"precip":0.0,"rh":94,"temp":5.9,"time":"2026-05-21T23:00Z","wind":10.0},{"cloud":95,"dark":true,"high":0,"local":"03:00","low":77,"mid":80,"precip":0.0,"rh":97,"temp":6.2,"time":"2026-05-22T00:00Z","wind":11.3},{"cloud":74,"dark":false,"high":25,"local":"04:00","low":58,"mid":19,"precip":0.0,"rh":97,"temp":6.0,"time":"2026-05-22T01:00Z","wind":10.3},{"cloud":94,"dark":false,"high":41,"local":"05:00","low":90,"mid":2,"precip":0.0,"rh":98,"temp":5.3,"time":"2026-05-22T02:00Z","wind":10.8},{"cloud":99,"dark":false,"high":95,"local":"06:00","low":73,"mid":23,"precip":0.0,"rh":97,"temp":5.7,"time":"2026-05-22T03:00Z","wind":11.3}],"forecast_source":"history","forecast_updated_at":"2026-10-13T18:24:24Z","limits":{"good_alt":30.0,"usable_alt":20.0},"night":{"dark_from":"2026-05-21T19:39:26Z","dark_hours":5.27,"dark_to":"2026-05-22T00:55:37Z","moon":{"illumination":0.334,"phase":"waxing crescent","waxing":true},"moon_free_dark_hours":2.45,"moonrise":"2026-05-22T08:45:33Z","moonset":"2026-05-21T22:27:03Z","sunrise":"2026-05-22T02:55:23Z","sunset":"2026-05-21T17:39:40Z","twilight":{"astronomical":{"end":"2026-05-21T19:39:26Z","start":"2026-05-22T00:55:37Z"},"civil":{"end":"2026-05-21T18:12:05Z","start":"2026-05-22T02:22:58Z"},"nautical":{"end":"2026-05-21T18:52:50Z","start":"2026-05-22T01:42:13Z"}},"window_end":"2026-05-22T09:00:00Z","window_start":"2026-05-21T09:00:00Z"},"night_date":"2026-05-21","site":{"elev_m":1750,"lat":41.693,"lon":24.739,"name":"NAO Rozhen"},"warnings":[]}