{"assessment":{"best_window":{"end":"2027-09-19T02:35Z","end_local":"05:35","hours":8.58,"label":"marginal","mean_quality":0.39,"start":"2027-09-18T18:00Z","start_local":"21:00"},"cost":{"altitude":0.0,"clouds":0.0,"darkness":2.41,"moon":5.59},"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":"Astronomically possible, with compromises \u2014 weather unknown","hourly":[{"alt":null,"cloud":null,"high":null,"iso":"2027-09-18T17:00Z","label":"poor","low":null,"mid":null,"moon_alt":-3,"precip":null,"q":0.15,"rh":null,"sky":"nautical twilight","temp":null,"time":"20:00","wind":null},{"alt":null,"cloud":null,"high":null,"iso":"2027-09-18T18:00Z","label":"marginal","low":null,"mid":null,"moon_alt":8,"precip":null,"q":0.59,"rh":null,"sky":"night","temp":null,"time":"21:00","wind":null},{"alt":null,"cloud":null,"high":null,"iso":"2027-09-18T19:00Z","label":"marginal","low":null,"mid":null,"moon_alt":19,"precip":null,"q":0.52,"rh":null,"sky":"night","temp":null,"time":"22:00","wind":null},{"alt":null,"cloud":null,"high":null,"iso":"2027-09-18T20:00Z","label":"marginal","low":null,"mid":null,"moon_alt":30,"precip":null,"q":0.45,"rh":null,"sky":"night","temp":null,"time":"23:00","wind":null},{"alt":null,"cloud":null,"high":null,"iso":"2027-09-18T21:00Z","label":"marginal","low":null,"mid":null,"moon_alt":41,"precip":null,"q":0.4,"rh":null,"sky":"night","temp":null,"time":"00:00","wind":null},{"alt":null,"cloud":null,"high":null,"iso":"2027-09-18T22:00Z","label":"marginal","low":null,"mid":null,"moon_alt":51,"precip":null,"q":0.35,"rh":null,"sky":"night","temp":null,"time":"01:00","wind":null},{"alt":null,"cloud":null,"high":null,"iso":"2027-09-18T23:00Z","label":"marginal","low":null,"mid":null,"moon_alt":59,"precip":null,"q":0.32,"rh":null,"sky":"night","temp":null,"time":"02:00","wind":null},{"alt":null,"cloud":null,"high":null,"iso":"2027-09-19T00:00Z","label":"marginal","low":null,"mid":null,"moon_alt":64,"precip":null,"q":0.31,"rh":null,"sky":"night","temp":null,"time":"03:00","wind":null},{"alt":null,"cloud":null,"high":null,"iso":"2027-09-19T01:00Z","label":"marginal","low":null,"mid":null,"moon_alt":63,"precip":null,"q":0.31,"rh":null,"sky":"night","temp":null,"time":"04:00","wind":null},{"alt":null,"cloud":null,"high":null,"iso":"2027-09-19T02:00Z","label":"marginal","low":null,"mid":null,"moon_alt":57,"precip":null,"q":0.33,"rh":null,"sky":"night","temp":null,"time":"05:00","wind":null},{"alt":null,"cloud":null,"high":null,"iso":"2027-09-19T03:00Z","label":"poor","low":null,"mid":null,"moon_alt":48,"precip":null,"q":0.18,"rh":null,"sky":"astronomical twilight","temp":null,"time":"06:00","wind":null},{"alt":null,"cloud":null,"high":null,"iso":"2027-09-19T04:00Z","label":"unusable","low":null,"mid":null,"moon_alt":38,"precip":null,"q":0.0,"rh":null,"sky":"civil twilight","temp":null,"time":"07:00","wind":null}],"peak_quality":0.59,"peak_sky":0.59,"quality_hours":3.67,"reasons":["moonlight cost 5.6 quality-hours","daylight and twilight cost 2.4 quality-hours"],"reference_hours":4.0,"score":null,"score_astronomy":54,"score_weather":null,"sky_hours":3.67,"verdict":"unknown","verdict_astronomy":"marginal","weather_known":false,"windows":[{"end":"2027-09-18T16:55Z","end_local":"19:55","hours":0.5,"label":"unusable","mean_quality":0.0,"start":"2027-09-18T16:25Z","start_local":"19:25"},{"end":"2027-09-18T17:30Z","end_local":"20:30","hours":0.58,"label":"poor","mean_quality":0.13,"start":"2027-09-18T16:55Z","start_local":"19:55"},{"end":"2027-09-18T17:50Z","end_local":"20:50","hours":0.33,"label":"marginal","mean_quality":0.31,"start":"2027-09-18T17:30Z","start_local":"20:30"},{"end":"2027-09-18T18:00Z","end_local":"21:00","hours":0.17,"label":"poor","mean_quality":0.3,"start":"2027-09-18T17:50Z","start_local":"20:50"},{"end":"2027-09-19T02:35Z","end_local":"05:35","hours":8.58,"label":"marginal","mean_quality":0.39,"start":"2027-09-18T18:00Z","start_local":"21:00"},{"end":"2027-09-19T03:40Z","end_local":"06:40","hours":1.08,"label":"poor","mean_quality":0.11,"start":"2027-09-19T02:35Z","start_local":"05:35"},{"end":"2027-09-19T04:05Z","end_local":"07:05","hours":0.42,"label":"unusable","mean_quality":0.0,"start":"2027-09-19T03:40Z","start_local":"06:40"}]},"calculation_version":"2026-10-10.1","forecast":[],"forecast_source":"none","forecast_updated_at":null,"limits":{"good_alt":30.0,"usable_alt":20.0},"night":{"dark_from":"2027-09-18T17:59:54Z","dark_hours":8.52,"dark_to":"2027-09-19T02:30:53Z","moon":{"illumination":0.911,"phase":"waning gibbous","waxing":false},"moon_free_dark_hours":0.0,"moonrise":"2027-09-18T17:15:54Z","moonset":"2027-09-19T07:34:08Z","sunrise":"2027-09-19T04:04:55Z","sunset":"2027-09-18T16:25:59Z","twilight":{"astronomical":{"end":"2027-09-18T17:59:54Z","start":"2027-09-19T02:30:53Z"},"civil":{"end":"2027-09-18T16:53:46Z","start":"2027-09-19T03:37:06Z"},"nautical":{"end":"2027-09-18T17:26:26Z","start":"2027-09-19T03:04:24Z"}},"window_end":"2027-09-19T09:00:00Z","window_start":"2027-09-18T09:00:00Z"},"night_date":"2027-09-18","site":{"elev_m":1750,"lat":41.693,"lon":24.739,"name":"NAO Rozhen"},"warnings":["No cloud data for this night (beyond the 4-day forecast, or not yet in the archive) \u2014 the score is geometry only."]}