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, and how much of each frame it fills. Click a cell for the full Bortle 1 to 9 table.
Telescope	In frame	Bortle 3 (rural)	Bortle 5 (suburban)	Bortle 7 (urban edge)
ZWO Seestar S5010 s subs	26%	24 min145 subs	38 min228 subs	1 h 38 min588 subs
ZWO Seestar S50 Pro10 s subs	13%	27 min161 subs	42 min250 subs	1 h 47 min640 subs
ZWO Seestar S3010 s subs	15%	27 min162 subs	41 min245 subs	1 h 41 min605 subs
ZWO Seestar S30 Pro10 s subs	8%	29 min172 subs	44 min266 subs	1 h 53 min676 subs
DwarfLab DWARF 315 s subs	11%	32 min129 subs	53 min214 subs	2 h 26 min585 subs
DwarfLab DWARF mini15 s subs	15%	24 min96 subs	38 min151 subs	1 h 38 min391 subs
DwarfLab Draco30 s subs	15%	19 min39 subs	31 min62 subs	1 h 21 min162 subs
DwarfLab DWARF II15 s subs	10%	1 h 43 min413 subs	2 h 21 min566 subs	5 h 08 min1,234 subs
Vaonis Vespera II10 s subs	13%	24 min145 subs	38 min228 subs	1 h 38 min588 subs
Vaonis Vespera Pro10 s subs	11%	58 min350 subs	1 h 27 min524 subs	3 h 34 min1,282 subs
Vaonis Vespera 310 s subs	13%	23 min138 subs	36 min217 subs	1 h 34 min563 subs
Vaonis Vespera Pro 210 s subs	11%	55 min331 subs	1 h 23 min498 subs	3 h 24 min1,226 subs
Unistellar eQuinox 24 s subs	32%	31 min465 subs	40 min594 subs	1 h 17 min1,156 subs
Unistellar Odyssey4 s subs	33%	2 h 43 min2,445 subs	3 h 14 min2,913 subs	5 h 30 min4,958 subs
Celestron Origin10 s subs	21%	6 min35 subs	10 min58 subs	27 min161 subs
Celestron Origin Mark II10 s subs	25%	7 min44 subs	13 min78 subs	37 min225 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.

Whirlpool Galaxy

How long with each smart telescope

Imaging the galaxy

Per-telescope pages