How long to image the NGC 891 with the Unistellar Odyssey
From a Bortle 6 suburban sky, the Unistellar Odyssey needs about 12 h (10,436 subs of 4 s) for a solid image of the NGC 891. A quick look takes 2 h 54 min; a showpiece 46 h. Under a Bortle 3 rural sky the solid figure drops to 7 h 43 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 40% 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 | 1 h 50 min1,651 subs | 7 h 20 min6,601 subs | 29 h26,402 subs |
| Bortle 2Typical dark site | 1 h 52 min1,680 subs | 7 h 28 min6,719 subs | 30 h26,873 subs |
| Bortle 3Rural | 1 h 56 min1,736 subs | 7 h 43 min6,941 subs | 31 h27,764 subs |
| Bortle 4Rural / suburban transition | 2 h 05 min1,871 subs | 8 h 19 min7,481 subs | 33 h29,924 subs |
| Bortle 5Suburban | 2 h 19 min2,085 subs | 9 h 16 min8,337 subs | 37 h33,346 subs |
| Bortle 6Bright suburban | 2 h 54 min2,609 subs | 12 h10,436 subs | 46 h41,742 subs |
| Bortle 7Suburban / urban transition | 4 h 01 min3,609 subs | 16 h14,435 subs | 64 h57,740 subs |
| Bortle 8City | 5 h 44 min5,162 subs | 23 h20,645 subs | 92 h82,580 subs |
| Bortle 9Inner city | 9 h 25 min8,473 subs | 38 h33,889 subs | 150+ h135,556 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 15 h of run time. That is more than one night: over 3 nights, about 5 h 01 min each. The Odyssey’s battery is rated at about 5 h, less near freezing, so each night needs an external power bank. (Bortle 6, solid image; we allow 30% over the integration time, and 30% off the battery for a November night.)
- USB power bank 20000mAh 5V 2.4AUnistellar says plain 5 V 2.4 A and warns against fast or adaptive chargers.
- 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 Odyssey →
How it frames
The NGC 891 is 13.5′ × 2.5′ across. The Odyssey frames 0.75° × 0.56° at 0.93″ per pixel, so it fills 40% of the frame’s short side.
About the NGC 891
A perfect edge-on spiral split by a dust lane. Faint per pixel; a dark sky or a long stack shows the lane.
Caldwell 23, Silver Sliver · Galaxy in Andromeda · magnitude 10.0 · 13.5′ × 2.5′ · best in Oct, Nov, Dec. 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 Unistellar Odyssey
Unistellar’s compact 85 mm with autofocus and tiny pixels. Sharp, but the fine sampling costs time on faint extended targets. The Odyssey Pro is the same telescope with an eyepiece added, so these figures apply to both.
Fixed 4 s subs in Enhanced Vision; they cannot be changed. No filter option; Unistellar says third-party filters cannot be fitted to the Odyssey.
The Odyssey uses fixed 4 s subs, so the only levers you have are the sky you shoot from, the filter, and total time.
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 891 from a Odyssey? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- NGC 891 with the ZWO Seestar S50: 2 h 44 min from Bortle 6
- NGC 891 with the ZWO Seestar S50 Pro: 3 h from Bortle 6
- NGC 891 with the ZWO Seestar S30: 2 h 53 min from Bortle 6
- NGC 891 with the ZWO Seestar S30 Pro: 3 h 10 min from Bortle 6
- NGC 891 with the DwarfLab DWARF 3: 3 h 58 min from Bortle 6
- NGC 891 with the DwarfLab DWARF mini: 2 h 43 min from Bortle 6
- NGC 891 with the DwarfLab Draco: 2 h 15 min from Bortle 6
- NGC 891 with the DwarfLab DWARF II: 9 h 24 min from Bortle 6
- NGC 891 with the Vaonis Vespera II: 2 h 44 min from Bortle 6
- NGC 891 with the Vaonis Vespera Pro: 6 h 08 min from Bortle 6
- NGC 891 with the Vaonis Vespera 3: 2 h 37 min from Bortle 6
- NGC 891 with the Vaonis Vespera Pro 2: 5 h 51 min from Bortle 6
- NGC 891 with the Unistellar eQuinox 2: 2 h 30 min from Bortle 6
- NGC 891 with the Celestron Origin: 43 min from Bortle 6
- NGC 891 with the Celestron Origin Mark II: 59 min from Bortle 6
All telescopes for the NGC 891 · All targets for the Odyssey