Will a target be observable from the National Astronomical Observatory Rozhen (41.693° N, 24.739° E, 1750 m) on a given night — and what does the night itself look like: sunset and twilights, the Moon, the target's altitude hour by hour, and the cloud forecast over the Rhodopes.
Try: M31 · M42 · V1057 Cyg · HD 189733 · NGC 7000 · Vega · 3C 273 · ← previous night · next night → · plan a whole night with several targets →
Bands: daylight → civil → nautical → astronomical twilight → night. Dashed grey: the Moon. Dashed lines: 20° (airmass ~2.9) and 30° (airmass 2.0).
No forecast this far ahead — Open-Meteo covers the next 4 days.
| local | sky | target alt | Moon alt | cloud % | low / mid / high | RH % | wind km/h | rain % | °C | quality |
|---|---|---|---|---|---|---|---|---|---|---|
| 18:00 | nautical twilight | 75° | 13 | — | — | — | — | — | — | poor 0.12 |
| 19:00 | night | 64° | 24 | — | — | — | — | — | — | good 0.75 |
| 20:00 | night | 53° | 35 | — | — | — | — | — | — | good 0.69 |
| 21:00 | night | 42° | 46 | — | — | — | — | — | — | good 0.61 |
| 22:00 | night | 32° | 55 | — | — | — | — | — | — | marginal 0.55 |
| 23:00 | night | 22° | 61 | — | — | — | — | — | — | marginal 0.31 |
| 00:00 | night | 13° | 63 | — | — | — | — | — | — | unusable 0.0 |
| 01:00 | night | 5° | 59 | — | — | — | — | — | — | unusable 0.0 |
| 02:00 | night | -2° | 51 | — | — | — | — | — | — | unusable 0.0 |
| 03:00 | night | -6° | 41 | — | — | — | — | — | — | unusable 0.0 |
| 04:00 | night | -9° | 31 | — | — | — | — | — | — | unusable 0.0 |
| 05:00 | night | -9° | 20 | — | — | — | — | — | — | unusable 0.0 |
| 06:00 | nautical twilight | -8° | 10 | — | — | — | — | — | — | unusable 0.0 |
Weather: none for this night. RH above ~90 % with little wind is the fog signature on this ridge.
The 20°/30° limits are the usual photometric ones (airmass ~2.9 / 2.0), not the mechanical limits of any instrument — those, the dome, and the observing schedule are the observatory's to confirm.
2026-10-10.1.All times are local (Europe/Sofia). The night runs from local noon to the next local noon.
curl -sS "https://devops.majbase.com/rozhen-planner/api?target=M31&date=2026-10-25"
curl -sS "https://devops.majbase.com/rozhen-planner/api?target=83.63+22.01" # RA Dec in degrees
curl -sS "https://devops.majbase.com/rozhen-planner/api" # just the night (Sun, Moon, clouds){
"night_date": "2026-10-09",
"site": {"name": "NAO Rozhen", "lat": 41.693, "lon": 24.739, "elev_m": 1750},
"night": {"sunset": "…Z", "sunrise": "…Z", "twilight": {"civil": {…}, "nautical": {…}, "astronomical": {…}},
"dark_from": "…Z", "dark_to": "…Z", "dark_hours": 9.55,
"moonrise": "…Z", "moonset": "…Z", "moon": {"illumination": 0.007, "phase": "new moon", "waxing": false},
"moon_free_dark_hours": 9.55},
"target": {"ra": 10.68, "dec": 41.27, "ra_of_date": 11.03, "dec_of_date": 41.41,
"transit": {"t": "…Z", "alt": 89.6, "az": 187.9, "airmass": 1.0},
"good_hours": 9.58, "usable_hours": 9.58, "moon_separation": 144.4,
"verdict": "good", "summary": "…", "resolved": {"name": "M31", "common_name": "Andromeda Galaxy", "type": "AGN"},
"track": [{"t": "…Z", "alt": 12.3, "az": 41.0, "airmass": 4.6}, …]},
"assessment": {"score": 84, "verdict": "good", "headline": "Worth it", "quality_hours": 3.4,
"best_window": {"label": "good", "start_local": "22:30", "end_local": "02:15", "hours": 3.75, "mean_quality": 0.82},
"windows": [{"label": "marginal", "start_local": "20:30", "end_local": "22:30", …}, …],
"hourly": [{"time": "21:00", "sky": "night", "alt": 45, "moon_alt": -12, "cloud": 20, "low": 5, "mid": 0, "high": 20,
"rh": 71, "wind": 9.4, "precip": 0, "temp": 6.1, "q": 0.78, "label": "good"}, …],
"reasons": ["cloud cover cost 2.1 quality-hours"], "hard_limit": null, "cost": {…}},
"forecast": [...hourly rows...], "forecast_source": "forecast", "forecast_updated_at": "…Z",
"calculation_version": "2026-10-10.1", "warnings": []
}Errors: {"error": "…", "code": "target_unresolved"} with HTTP 400 when a target is given but cannot be resolved; an unparseable date is not an error — tonight is used and a warning is added. date is the evening the night starts on, as 2026-10-09, 2026.10.09 or 09.10.2026; omitted = tonight. The response carries night (sunset/sunrise, twilights, dark window, Moon), target (coordinates, transit, dark hours above the limits, Moon separation, verdict of good / marginal / poor / none / never, and the 5-minute track of altitude, azimuth and airmass) and forecast (hourly rows for the night). Times are ISO 8601 UTC.