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Crescent Nebula (NGC 6888) - HOO

Wolf-Rayet stellar wind bubble in Cygnus captured with Ha and OIII filters

Crescent Nebula (NGC 6888) - HOO

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Deep Space Capture

Technical Specifications

Resolution: 6000x4000 (drizzle integrated)

Integration: 122 Ha + 98 OIII subexposures × 300s each

Captured: Captured over two nights with exceptional seeing and transparency

Equipment: Redcat71 refractor (350mm) with ZWO ASI2600MM Pro camera on Advanced VX mount

Location: Backyard location, Bortle 7 light pollution zone

Processing Workflow

Total integration time: ~18 hours across Ha and OIII filters
ZWO 7nm narrowband filters: Ha and OIII with 5-position filter wheel
Every third sub-exposure dithered by 2 pixels for improved sampling
Drizzle integration for enhanced resolution and detail
Guided using ZWO 30mm mini guide scope with ASI290MM mini camera
Controlled via ZWO ASIAir Plus with Electronic Auto Focuser
HOO bicolor processing optimized for Wolf-Rayet nebula structure

Scientific Context

The Crescent Nebula (NGC 6888) is a spectacular example of a Wolf-Rayet nebula, formed by the intense stellar winds from the central Wolf-Rayet star WR 136 (HD 192163). Located approximately 5,000 light-years away in the constellation Cygnus, this emission nebula showcases one of the most dramatic phases of stellar evolution.

The nebula's distinctive crescent shape is the result of a collision between two different stellar winds from the same star. The fast-moving stellar wind from the current Wolf-Rayet phase (traveling at speeds up to 1,700 km/s) collides with and energizes the slower-moving wind that was ejected when the star was in its red giant phase approximately 250,000 to 400,000 years ago. This collision creates the characteristic shock-heated bubble structure we see today.

This HOO (Hydrogen-alpha and Oxygen-III) bicolor image reveals the complex filamentary structure throughout the nebula. The Ha emission (mapped to red/orange) primarily traces the dense shock fronts where the stellar winds collide, while the OIII emission (mapped to blue/cyan) highlights regions of highly ionized oxygen created by the intense ultraviolet radiation from the central Wolf-Rayet star.

Wolf-Rayet stars like WR 136 are among the most massive and luminous stars known, representing a brief but spectacular phase in the evolution of very massive stars (>25 solar masses) as they approach the end of their lives. The nebula spans approximately 25 light-years across and continues to expand at speeds of several tens of kilometers per second.