How long to image the Crescent Nebula with the Unistellar Odyssey
From a Bortle 6 suburban sky, the Unistellar Odyssey needs about 20 h (17,741 subs of 4 s) for a solid image of the Crescent Nebula. A quick look takes 4 h 56 min; a showpiece 79 h. Under a Bortle 3 rural sky the solid figure drops to 13 h. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 53% 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 | 3 h 06 min2,789 subs | 12 h11,154 subs | 50 h44,616 subs |
| Bortle 2Typical dark site | 3 h 09 min2,840 subs | 13 h11,357 subs | 50 h45,425 subs |
| Bortle 3Rural | 3 h 16 min2,935 subs | 13 h11,739 subs | 52 h46,956 subs |
| Bortle 4Rural / suburban transition | 3 h 31 min3,167 subs | 14 h12,667 subs | 56 h50,665 subs |
| Bortle 5Suburban | 3 h 56 min3,534 subs | 16 h14,136 subs | 63 h56,542 subs |
| Bortle 6Bright suburban | 4 h 56 min4,436 subs | 20 h17,741 subs | 79 h70,963 subs |
| Bortle 7Suburban / urban transition | 6 h 50 min6,153 subs | 27 h24,611 subs | 110+ h98,441 subs |
| Bortle 8City | 9 h 48 min8,820 subs | 39 h35,277 subs | 160+ h141,105 subs |
| Bortle 9Inner city | 16 h14,506 subs | 64 h58,024 subs | 260+ h232,093 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 26 h of run time. That is more than one night: over 4 nights, about 6 h 24 min each. The Odyssey’s battery is rated at about 5 h, so each night needs an external power bank. (Bortle 6, solid image; we allow 30% over the integration time.)
- 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.
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How it frames
The Crescent Nebula is 18′ × 12′ across. The Odyssey frames 0.75° × 0.56° at 0.93″ per pixel, so it fills 53% of the frame’s short side.
Filters
The Crescent Nebula is an emission target, where a dual-band filter would normally cut the time several-fold from a lit sky, but the Odyssey has no dual-band option: No filter option; Unistellar says third-party filters cannot be fitted to the Odyssey. The figures above are for the No filter position, and a darker sky is the lever that remains.
About the Crescent Nebula
A shell blown by a Wolf-Rayet star, bright in H-alpha with a faint OIII skin. Small, so the bigger scopes do it justice.
NGC 6888, Caldwell 27 · Emission nebula in Cygnus · magnitude 7.4 · 18′ × 12′ · best in Jul, Aug, Sep. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.
Emission nebulae glow in a few narrow lines, mostly hydrogen-alpha (deep red) and doubly ionised oxygen (teal). A dual-band filter passes those lines and blocks most skyglow, which is why it cuts the time needed from a suburban sky so dramatically. Use it. From a genuinely dark site the gain is smaller because there is less skyglow to block, and read noise becomes the limit, which is where longer subs (EQ mode, or Expert Mode on a Vespera) earn their keep.
Stars lose colour through a dual-band filter; a short broadband stack blended in fixes that if you care.
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 Crescent Nebula from a Odyssey? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- Crescent Nebula with the ZWO Seestar S50: 2 h 49 min from Bortle 6
- Crescent Nebula with the ZWO Seestar S50 Pro: 3 h 10 min from Bortle 6
- Crescent Nebula with the ZWO Seestar S30: 3 h 19 min from Bortle 6
- Crescent Nebula with the ZWO Seestar S30 Pro: 3 h 25 min from Bortle 6
- Crescent Nebula with the DwarfLab DWARF 3: 3 h 27 min from Bortle 6
- Crescent Nebula with the DwarfLab DWARF mini: 2 h 47 min from Bortle 6
- Crescent Nebula with the DwarfLab Draco: 2 h 14 min from Bortle 6
- Crescent Nebula with the DwarfLab DWARF II: 16 h from Bortle 6
- Crescent Nebula with the Vaonis Vespera II: 4 h 37 min from Bortle 6
- Crescent Nebula with the Vaonis Vespera Pro: 10 h from Bortle 6
- Crescent Nebula with the Vaonis Vespera 3: 4 h 24 min from Bortle 6
- Crescent Nebula with the Vaonis Vespera Pro 2: 9 h 52 min from Bortle 6
- Crescent Nebula with the Unistellar eQuinox 2: 4 h 14 min from Bortle 6
- Crescent Nebula with the Celestron Origin: 1 h 13 min from Bortle 6
- Crescent Nebula with the Celestron Origin Mark II: 1 h 40 min from Bortle 6
All telescopes for the Crescent Nebula · All targets for the Odyssey