How Many Subs

NGC 891

Caldwell 23, Silver Sliver · Galaxy in Andromeda

Magnitude
10.0
Size
13.5′ × 2.5′
Effective surface brightness
22.4 mag/arcsec²
Best months
Oct, Nov, Dec
Declination
+42°
Filter
None (broadband target)

A perfect edge-on spiral split by a dust lane. Faint per pixel; a dark sky or a long stack shows the lane.

Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.

How long with each smart telescope

Total integration for a solid image of the NGC 891, default sub length, recommended filter. Click a cell for the full Bortle 1 to 9 table.
TelescopeBortle 3 (rural)Bortle 5 (suburban)Bortle 7 (urban edge)
ZWO Seestar S5010 s subs1 h 26 min514 subs2 h 07 min760 subs5 h 06 min1,836 subs
ZWO Seestar S50 Pro10 s subs1 h 09 min412 subs1 h 53 min678 subs5 h 07 min1,842 subs
ZWO Seestar S3010 s subs1 h 02 min370 subs1 h 43 min616 subs4 h 42 min1,691 subs
ZWO Seestar S30 Pro10 s subs1 h 14 min442 subs2 h722 subs5 h 24 min1,946 subs
DwarfLab Dwarf 315 s subs1 h 39 min397 subs2 h 42 min650 subs7 h 19 min1,758 subs
DwarfLab Dwarf Mini15 s subs55 min221 subs1 h 36 min385 subs4 h 35 min1,102 subs
DwarfLab Dwarf II15 s subs4 h 39 min1,116 subs6 h 33 min1,572 subs15 h3,564 subs
Vaonis Vespera II10 s subs1 h 02 min370 subs1 h 43 min616 subs4 h 42 min1,691 subs
Vaonis Vespera Pro10 s subs3 h 03 min1,097 subs4 h 29 min1,615 subs11 h3,876 subs
Unistellar eQuinox 24 s subs1 h 26 min1,289 subs1 h 51 min1,673 subs3 h 43 min3,349 subs
Unistellar Odyssey4 s subs7 h 43 min6,941 subs9 h 16 min8,337 subs16 h14,435 subs
Celestron Origin10 s subs14 min86 subs26 min156 subs1 h 17 min461 subs

Open in the calculator

Imaging the galaxy

Galaxies are broadband targets: their light is mostly starlight spread across the spectrum, so a dual-band filter throws most of it away and makes things slower, not faster. Shoot without a filter (or with a plain UV/IR cut) and rely on total time and a dark sky. The core of a galaxy is usually many times brighter than its outer disc, so a short stack shows the nucleus long before the arms; the figures here are for the arms and disc, not the core.

Field rotation in Alt-Az mode crops the edges of the stack over a long session, so on a big galaxy re-centre now and then or use EQ mode where your scope supports it.

Per-telescope pages