Year-round target planner

William Optics RedCat 71 · ZWO ASI2600MM Pro · AM3 · hosted at ~38.2°N, 6.6°W (Extremadura, Spain)

3.85° × 2.57° field 2.22″/px image scale 350 mm f/4.9 28.3 mm sensor diagonal in a 45 mm image circle 7 × 36 mm L R G B S H O

The dark-hour budget

Astronomical night at 38.2°N, computed at 10-minute resolution across a full year, then discounted by a weather yield. Pick the yield yourself — the published figures disagree with each other, so this is an assumption rather than a measurement, and everything downstream moves with it. Moonless hours are the budget for broadband LRGB; the moonlit remainder is where narrowband earns its keep.

Moonless dark hours Moonlit dark hours

Targets

What this rig is actually good at

The 3.85° field is the whole point

Roughly fifteen well-known objects land between 40% and 95% of the frame width — the Veil complex, North America + Pelican together, IC 1396, the California Nebula, Simeis 147, IC 405 + IC 410 + M38, the Rosette, Sh2-216, the Sadr region. At 350 mm you frame these in a single shot with breathing room, which almost no other focal length manages.

Guiding demand is trivially low

At 2.22″/px, 1.0″ RMS guiding is 0.45 px. The AM3's strain-wave drive plus a 32 mm guide scope is comfortably inside that, and the RedCat's 45 mm image circle leaves a 8 mm margin around the APS-C diagonal — corner illumination and tilt are non-issues. Nothing in this optical train is the limiting factor.

Anything under ~15′ is a context shot, not a detail shot

M51, M27, NGC 6888, the Iris, the Cocoon, Thor's Helmet, M106, the Leo Triplet and M81/M82 all span fewer than 400 px on the long axis. Shoot them for the faint surrounding structure — tidal shells, outer OIII halos, integrated flux — which is exactly what a dark remote site is for. Chasing core detail is the wrong use of this setup.

Everything below about −25° declination is lost

Rho Ophiuchi, M8 + M20, Sh2-308 and NGC 1360 never exceed 30° altitude from 38.2°N — zero hours per year above that threshold. M16 + M17 peak at 37° and M24 at 33°. If the southern Milky Way matters to you, that is the one thing a Spanish host cannot give you, and it is the single strongest argument for a second rig in Chile later on.

March through May is the thin stretch — but not empty

Only eleven targets peak in spring, and 265 of their 430 demanded hours are broadband-only, competing for roughly 166 moonless hours in that window at a middling weather yield. The saving grace is that Cygnus clears 40° in the second half of the night from April onward, so the moonlit spring hours have narrowband work waiting. Plan spring deliberately: one deep IFN or Virgo project for dark time, early Cygnus panels for everything else.

So — will it have enough to do?