Custom location
1 Paste your target sample
One target per line. Same formats as CoordSwap — name, RA, Dec or just RA Dec. Use # for comments.
Parsed 0 targets.
2 Set night + observatory
Custom location
3 Run
4 Results
Custom location
Observability + airmass planner
Visibility curves, airmass, twilight times, Moon angular separation and illumination — all in one plot, for any night, from 41 of the world's major optical, infrared, and radio observatories. Single target or whole proposal sample. Validated against Meeus.
Custom location
One target per line. Same formats as CoordSwap — name, RA, Dec or just RA Dec. Use # for comments.
Parsed 0 targets.
Custom location
Custom location
About
For one target on one night at one observatory: altitude curve over the entire night, Sun and Moon altitude curves, four twilight thresholds (sunset, civil −6°, nautical −12°, astronomical −18°), continuous dark-hour window above 30° altitude (airmass < 2), peak altitude with minimum airmass, and Moon angular separation + illumination during dark time.
For a target sample: tabular best-window summary for all targets at once, downloadable as CSV with full night metadata.
Sun position via Meeus (1998) Ch. 25 — accurate to ~0.01° at equinoxes and solstices. Moon position via full Meeus Ch. 47 (60 longitude/distance + 60 latitude periodic terms + planetary perturbations) — apogee/perigee distances within ~500 km of almanac values, eclipse moments coincident to <0.5°. Airmass via Pickering (2002), valid to X ≈ 38. Twilights solved by bisection on the Sun's altitude. Sidereal time from Meeus eq. 12.4. Twilight times match Time-and-Date.com cross-checks for Mauna Kea within 2 minutes.
Optical/IR: Keck I/II, Subaru, Gemini-N/S, CFHT, IRTF, UKIRT, SMA, DKIST, Pan-STARRS, VLT (UT 1–4), ELT, ESO 3.6 m, NTT, Magellan, SOAR, Rubin/LSST, GTC, WHT, NOT, TNG, LBT, MMT, Mayall/KPNO, APO 3.5 m, HET, Hale/Palomar, Lick, HCT, LAMOST, Seimei, AAT, SALT, BTA-6. Radio/submm: ALMA, APEX, VLA, GBT, Parkes, Effelsberg, GMRT.
Don't see yours? Use Custom location at the top of
the observatory dropdown — give lat, lon, elevation, and IANA
timezone (e.g. Asia/Taipei).
Atmospheric refraction is not applied to the target altitude (it only changes airmass by ~0.5% above 30°). Topocentric parallax for the Moon (~1°) is also not applied — the geocentric Moon position is adequate for separation/illumination but if the Moon is your primary target use a dedicated lunar ephemeris. For space observatories (JWST, HST, etc.), this tool is not the right one; field-of-regard constraints differ fundamentally.
Part of the EuKosmos research-tool family by M. Rahaman. Sister tools: astrodeepsearch, coordswap, kosmocal, scical.