How Many Subs

Whirlpool Galaxy

M51, NGC 5194 · Galaxy in Canes Venatici

Magnitude
8.4
Size
11′ × 7′
Effective surface brightness
21.7 mag/arcsec²
Best months
Mar, Apr, May
Declination
+47°
Filter
None (broadband target)

The classic face-on spiral with its companion tugging at one arm. Small in a smart scope but bright; the arms appear within an hour, the tidal bridge needs several.

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 Whirlpool Galaxy, 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 subs32 min193 subs46 min276 subs1 h 46 min637 subs
ZWO Seestar S50 Pro10 s subs27 min161 subs42 min250 subs1 h 47 min640 subs
ZWO Seestar S3010 s subs24 min145 subs38 min228 subs1 h 38 min588 subs
ZWO Seestar S30 Pro10 s subs29 min172 subs44 min266 subs1 h 53 min676 subs
DwarfLab Dwarf 315 s subs39 min155 subs60 min240 subs2 h 33 min611 subs
DwarfLab Dwarf Mini15 s subs22 min88 subs36 min143 subs1 h 36 min384 subs
DwarfLab Dwarf II15 s subs1 h 43 min413 subs2 h 21 min566 subs5 h 08 min1,234 subs
Vaonis Vespera II10 s subs24 min145 subs38 min228 subs1 h 38 min588 subs
Vaonis Vespera Pro10 s subs1 h 09 min412 subs1 h 37 min585 subs3 h 44 min1,344 subs
Unistellar eQuinox 24 s subs31 min465 subs40 min594 subs1 h 17 min1,156 subs
Unistellar Odyssey4 s subs2 h 43 min2,445 subs3 h 14 min2,913 subs5 h 30 min4,958 subs
Celestron Origin10 s subs6 min35 subs10 min58 subs27 min161 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