How long to image the NGC 2903 with the ZWO Seestar S30
From a Bortle 6 suburban sky, the ZWO Seestar S30 needs about 2 h 28 min (890 subs of 10 s) for a solid image of the NGC 2903. A quick look takes 37 min; a showpiece 9 h 53 min. Under a Bortle 3 rural sky the solid figure drops to 1 h 01 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 18% of the frame’s short side.
| Sky | Quick lookTarget obvious, still noisy | SolidClean enough to share | ShowpieceSmooth faint detail, print-worthy |
|---|---|---|---|
| Bortle 1Excellent dark site | 13 min79 subs | 52 min314 subs | 3 h 29 min1,255 subs |
| Bortle 2Typical dark site | 14 min83 subs | 55 min332 subs | 3 h 41 min1,325 subs |
| Bortle 3Rural | 15 min92 subs | 1 h 01 min365 subs | 4 h 03 min1,459 subs |
| Bortle 4Rural / suburban transition | 19 min112 subs | 1 h 14 min446 subs | 4 h 57 min1,784 subs |
| Bortle 5Suburban | 24 min144 subs | 1 h 36 min575 subs | 6 h 23 min2,298 subs |
| Bortle 6Bright suburban | 37 min223 subs | 2 h 28 min890 subs | 9 h 53 min3,560 subs |
| Bortle 7Suburban / urban transition | 1 h 02 min373 subs | 4 h 08 min1,491 subs | 17 h5,964 subs |
| Bortle 8City | 1 h 41 min607 subs | 6 h 44 min2,425 subs | 27 h9,698 subs |
| Bortle 9Inner city | 3 h 04 min1,104 subs | 12 h4,415 subs | 49 h17,660 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 3 h 13 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, and 30% off the battery for a February night.)
- USB-C power bank 10000mAh 5V 3A6,000 mAh inside; a 10,000 mAh 5 V 3 A bank roughly doubles a session.
- Seestar S30 dew shieldHeater is built in; a cheap shield reduces dew and stray light.
- red LED head torchRed light keeps your night vision; white light costs you twenty minutes of dark adaptation every time.
- hand warmers long lastingAir-activated packs give hours of heat for the person; winter nights are long and you spend most of them standing still.
Affiliate links: the retailer pays us a small commission and you pay the same price. These are search links to the named product, not endorsements of a particular listing; check the listing matches your model.
Everything that fits the Seestar S30 →
How it frames
The NGC 2903 is 12.6′ × 6′ across. The Seestar S30 frames 2.13° × 1.20° at 3.99″ per pixel, so it fills 18% 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 | 1 h 01 min365 subs | 1 h 36 min575 subs | 4 h 08 min1,491 subs |
| 20 s | 49 min147 subs | 1 h 24 min252 subs | 3 h 57 min711 subs |
| 30 s | 45 min91 subs | 1 h 20 min161 subs | 3 h 53 min466 subs |
| 60 s | 41 min42 subs | 1 h 16 min77 subs | 3 h 49 min229 subs |
Leave the dual-band filter out for the NGC 2903. 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 14 times slower.
About the NGC 2903
A bright barred spiral below the Sickle of Leo that Messier somehow missed. Bright core, well-defined arms.
UGC 5079 · Galaxy in Leo · magnitude 9.0 · 12.6′ × 6′ · best in Jan, Feb, Mar. 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.
Have an image of the NGC 2903 from a Seestar S30? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- NGC 2903 with the ZWO Seestar S50: 2 h 21 min from Bortle 6
- NGC 2903 with the ZWO Seestar S50 Pro: 2 h 34 min from Bortle 6
- NGC 2903 with the ZWO Seestar S30 Pro: 2 h 44 min from Bortle 6
- NGC 2903 with the DwarfLab DWARF 3: 3 h 25 min from Bortle 6
- NGC 2903 with the DwarfLab DWARF mini: 2 h 20 min from Bortle 6
- NGC 2903 with the DwarfLab Draco: 1 h 56 min from Bortle 6
- NGC 2903 with the DwarfLab DWARF II: 8 h 04 min from Bortle 6
- NGC 2903 with the Vaonis Vespera II: 2 h 21 min from Bortle 6
- NGC 2903 with the Vaonis Vespera Pro: 5 h 16 min from Bortle 6
- NGC 2903 with the Vaonis Vespera 3: 2 h 15 min from Bortle 6
- NGC 2903 with the Vaonis Vespera Pro 2: 5 h 01 min from Bortle 6
- NGC 2903 with the Unistellar eQuinox 2: 2 h 08 min from Bortle 6
- NGC 2903 with the Unistellar Odyssey: 9 h 55 min from Bortle 6
- NGC 2903 with the Celestron Origin: 37 min from Bortle 6
- NGC 2903 with the Celestron Origin Mark II: 51 min from Bortle 6
All telescopes for the NGC 2903 · All targets for the Seestar S30