How long should I image the Whirlpool Galaxy with the Seestar S30 from a Bortle 6 sky?

About 1 h 01 min of total integration for a solid image, or 4 h 05 min for a showpiece. A quick look takes 15 min.

How many subs is that on the Seestar S30?

At the default 10 s sub length, 369 subs for a solid image from Bortle 6 and 162 from Bortle 3.

Does a dual-band filter help on the Whirlpool Galaxy?

No. The Whirlpool Galaxy is a broadband target and a dual-band filter blocks most of its light. Shoot without a filter.

How long to image the Whirlpool Galaxy with the ZWO Seestar S30

From a Bortle 6 suburban sky, the ZWO Seestar S30 needs about 1 h 01 min (369 subs of 10 s) for a solid image of the Whirlpool Galaxy. A quick look takes 15 min; a showpiece 4 h 05 min. Under a Bortle 3 rural sky the solid figure drops to 27 min. At Bortle 6 the limit is skyglow, so a darker site or a filter helps more than longer subs. In this scope's field it fills 15% of the frame’s short side.

Whirlpool Galaxy with the ZWO Seestar S30: 10 s subs.
Sky	Quick lookTarget obvious, still noisy	SolidClean enough to share	ShowpieceSmooth faint detail, print-worthy
Bortle 1Excellent dark site	6 min36 subs	24 min142 subs	1 h 34 min566 subs
Bortle 2Typical dark site	6 min38 subs	25 min149 subs	1 h 39 min594 subs
Bortle 3Rural	7 min41 subs	27 min162 subs	1 h 48 min647 subs
Bortle 4Rural / suburban transition	8 min49 subs	32 min194 subs	2 h 09 min774 subs
Bortle 5Suburban	10 min62 subs	41 min245 subs	2 h 43 min977 subs
Bortle 6Bright suburban	15 min93 subs	1 h 01 min369 subs	4 h 05 min1,473 subs
Bortle 7Suburban / urban transition	25 min152 subs	1 h 41 min605 subs	6 h 43 min2,419 subs
Bortle 8City	40 min243 subs	2 h 42 min972 subs	11 h3,888 subs
Bortle 9Inner city	1 h 13 min439 subs	4 h 53 min1,756 subs	20 h7,021 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 1 h 20 min of run time. The Seestar S30’s battery (rated about 6 h) should cover it; a power bank still keeps the phone running the app alive. (Bortle 6, solid image; we allow 30% over the integration time.)

USB-C power bank 10000mAh 5V 3A6,000 mAh inside; a 10,000 mAh 5 V 3 A bank roughly doubles a session.
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Seestar S30 dew shieldHeater is built in; a cheap shield reduces dew and stray light.
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red LED head torchRed light keeps your night vision; white light costs you twenty minutes of dark adaptation every time.
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Everything that fits the Seestar S30 →

How it frames

The Whirlpool Galaxy is 11′ × 7′ across. The Seestar S30 frames 2.13° × 1.20° at 3.99″ per pixel, so it fills 15% of the frame’s short side.

Longer subs

10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, which needs the TH10 head. Time for a solid image by sub length:

Sub length	Bortle 3	Bortle 5	Bortle 7
10 s	27 min162 subs	41 min245 subs	1 h 41 min605 subs
20 s	22 min67 subs	36 min109 subs	1 h 36 min289 subs
30 s	21 min42 subs	34 min69 subs	1 h 35 min190 subs
60 s	30 min30 subs	33 min33 subs	1 h 33 min94 subs

Leave the dual-band filter out for the Whirlpool Galaxy. It is a galaxy, and it shines right across the spectrum. A dual-band filter keeps two emission lines and throws the rest away, so most of the light you came for is being stopped along with the sky. From a Bortle 6 sky it would be roughly 13 times slower.

About the Whirlpool Galaxy

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.

M51, NGC 5194 · Galaxy in Canes Venatici · magnitude 8.4 · 11′ × 7′ · best in Mar, Apr, May. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.

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.

About the ZWO Seestar S30

Wider and lighter than the S50 with the same 2.9 µm pixels, so its per-pixel speed on extended targets is close despite the smaller aperture. Ideal for big nebulae.

10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, which needs the TH10 head. Built-in UV/IR-cut, dual-band (OIII 30 nm / Hα 20 nm) and dark filters.

Longer subs matter most under dark skies, where read noise rather than skyglow sets the floor. From a city the difference between 10 s and 60 s subs is small; from a rural site it can halve the total time, especially with a dual-band filter in place.

Stack across nights. Every smart scope app can continue a stack or you can combine the saved frames on a computer; the figures here are totals, not single-session limits.

Where to buy the Seestar S30ZWO store Direct Amazon UK Amazon USThe ZWO store link is a plain link; the others are affiliate links. As an Amazon Associate I earn from qualifying purchases, at no cost to you.

Imaged the Whirlpool Galaxy with your Seestar S30? Did the solid figure match?Anonymous, one tap. It is how the model gets calibrated.

Have an image of the Whirlpool Galaxy from a Seestar S30? Email it with your total time and sky to [email protected] and it goes here, credited.

Same target, other telescopes

All telescopes for the Whirlpool Galaxy · All targets for the Seestar S30