M109

NGC 3992 · Galaxy in Ursa Major

Magnitude: 9.8
Size: 7.6′ × 4.7′
Effective surface brightness: 22.3 mag/arcsec²
Best months: Feb, Mar, Apr
Declination: +53°
Filter: None (broadband target)

A barred spiral next to Phecda in the Plough. Faint outer arms, bright bar.

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 M109, 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	18%	1 h 27 min521 subs	2 h 23 min860 subs	6 h 30 min2,341 subs
ZWO Seestar S50 Pro10 s subs	9%	1 h 37 min581 subs	2 h 38 min947 subs	7 h 05 min2,549 subs
ZWO Seestar S3010 s subs	11%	1 h 38 min591 subs	2 h 35 min930 subs	6 h 42 min2,411 subs
ZWO Seestar S30 Pro10 s subs	6%	1 h 44 min623 subs	2 h 48 min1,008 subs	7 h 29 min2,693 subs
DwarfLab DWARF 315 s subs	8%	1 h 53 min452 subs	3 h 20 min801 subs	9 h 41 min2,326 subs
DwarfLab DWARF mini15 s subs	11%	1 h 26 min343 subs	2 h 22 min569 subs	6 h 29 min1,557 subs
DwarfLab Draco30 s subs	10%	1 h 09 min139 subs	1 h 56 min233 subs	5 h 22 min645 subs
DwarfLab DWARF II15 s subs	7%	6 h 30 min1,559 subs	9 h 07 min2,187 subs	21 h4,929 subs
Vaonis Vespera II10 s subs	9%	1 h 27 min521 subs	2 h 23 min860 subs	6 h 30 min2,341 subs
Vaonis Vespera Pro10 s subs	8%	3 h 34 min1,284 subs	5 h 33 min1,997 subs	14 h5,110 subs
Vaonis Vespera 310 s subs	9%	1 h 22 min493 subs	2 h 16 min819 subs	6 h 13 min2,241 subs
Vaonis Vespera Pro 210 s subs	8%	3 h 22 min1,211 subs	5 h 16 min1,895 subs	14 h4,885 subs
Unistellar eQuinox 24 s subs	22%	2 h1,795 subs	2 h 35 min2,322 subs	5 h 09 min4,630 subs
Unistellar Odyssey4 s subs	23%	11 h9,627 subs	13 h11,548 subs	22 h19,943 subs
Celestron Origin10 s subs	15%	20 min122 subs	36 min218 subs	1 h 46 min638 subs
Celestron Origin Mark II10 s subs	17%	25 min150 subs	48 min289 subs	2 h 29 min894 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.

M109

How long with each smart telescope

Imaging the galaxy

Per-telescope pages