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.
Mean cloud cover during astronomical night: 26%· what it was: ERA5 reanalysis
19:00cloud cover % per hour (dark = night)08:00
Telescopes at Rozhen
2 m RCC (Zeiss) — imaging at the RC focus, spectroscopy at the Coudé focus
1.5 m AZ1500 (robotic) — photometry; in operation since 2023
50/70 cm Schmidt — wide field, photometry of fields and asteroids
60 cm Cassegrain — photometry
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.
ℹ️ How it is computed, and how far to trust it
Sun and Moon from Meeus' Astronomical Algorithms: low-precision solar position (~1′) and a truncated lunar series (~0.3°). Rise/set use the standard horizons (−0.833° Sun, +0.125° Moon); times are good to a minute or two, which is all a plan needs.
Target altitude is plain spherical trigonometry from J2000 coordinates and local sidereal time, every 5 minutes; airmass is Kasten & Young. Precession to date is ignored (<0.3° in 2026, invisible at this scale).
Names go to CDS Sesame (SIMBAD / NED / VizieR). Solar-system bodies are not resolved — give coordinates for the night from JPL Horizons.
Weather is Open-Meteo: the hourly model forecast at the observatory's coordinates and altitude for the coming 4 days (refreshed every 30 minutes), and for past nights the ERA5 reanalysis — hourly cloud cover reconstructed from observations, 1940 onwards, about 5 days behind real time. Mountain weather is local; neither knows about the Rhodope fog in the valley below.
All times are local (Europe/Sofia). The night runs from local noon to the next local noon.
💡 Show API usage examples (cURL)
curl -sS "https://devops.majbase.com/rozhen-planner/api?target=M31&date=2026-09-27"
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)
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.
