Rozhen Observing Planner

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 →

Bands: daylight → civil → nautical → astronomical twilight → night. Dashed grey: the Moon. Dashed lines: 20° (airmass ~2.9) and 30° (airmass 2.0).

Night of Saturday, 03 October 2026

Sun

Sunset 18:59 · sunrise 07:20
Civil twilight ends 19:27 · begins 06:53
Nautical ends 19:59 · begins 06:20
Astronomical night 20:31 → 05:48 (9.28 h)

Moon — waning crescent, 46% lit

Moonrise 23:59 · moonset 14:55
Moon-free dark time: 3.45 h of 9.28 h

Clouds over Rozhen

No forecast this far ahead — Open-Meteo covers the next 4 days.

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's hourly model forecast at the observatory's coordinates and altitude, refreshed every 30 minutes. Mountain weather is local; the model does not know 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=2026-10-03"
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)

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.