How Many Subs

Pinwheel Galaxy

M101, NGC 5457 · Galaxy in Ursa Major

Magnitude
7.9
Size
29′ × 27′
Effective surface brightness
22.8 mag/arcsec²
Best months
Apr, May, Jun
Declination
+54°
Filter
None (broadband target)

Big, face-on and faint. Its total magnitude is flattering; spread over half a degree the arms are dim and demand hours, especially from suburban skies.

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 Pinwheel 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 subs2 h 22 min850 subs3 h 32 min1,272 subs8 h 40 min3,120 subs
ZWO Seestar S50 Pro10 s subs1 h 52 min672 subs3 h 08 min1,129 subs8 h 41 min3,128 subs
ZWO Seestar S3010 s subs1 h 40 min602 subs2 h 51 min1,025 subs7 h 59 min2,873 subs
ZWO Seestar S30 Pro10 s subs2 h722 subs3 h 20 min1,203 subs9 h 11 min3,306 subs
DwarfLab Dwarf 315 s subs2 h 42 min648 subs4 h 31 min1,084 subs12 h2,986 subs
DwarfLab Dwarf Mini15 s subs1 h 29 min358 subs2 h 40 min639 subs7 h 48 min1,871 subs
DwarfLab Dwarf II15 s subs7 h 44 min1,856 subs11 h2,639 subs25 h6,061 subs
Vaonis Vespera II10 s subs1 h 40 min602 subs2 h 51 min1,025 subs7 h 59 min2,873 subs
Vaonis Vespera Pro10 s subs5 h 03 min1,816 subs7 h 31 min2,705 subs18 h6,590 subs
Unistellar eQuinox 24 s subs2 h 24 min2,164 subs3 h 08 min2,823 subs6 h 20 min5,702 subs
Unistellar Odyssey4 s subs13 h11,739 subs16 h14,136 subs27 h24,611 subs
Celestron Origin10 s subs23 min138 subs43 min258 subs2 h 10 min782 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