Sh2-129 and OU4 – the Flying Bat and Giant Squid Nebula
The emission nebula Sh2-129 lies about 2,300 light years away in the constellation Cepheus and measures over 100 light years in diameter. Its reddish glow comes from the Hα radiation of ionised hydrogen, excited to glow by the intense UV radiation of young, hot stars — in particular the O-star system HR 8119.
Inside this nebula sits OU4, the so-called Giant Squid Nebula. It is an enormous bipolar structure of ionised oxygen ([O III] emission), over 50 light years long. The bluish glow of OU4 is extremely faint, with an estimated surface brightness of about 25 mag/arcsec², which makes it observable only with very deep exposures and narrowband filters.
The origin of OU4 is still not clearly established: it is probably a massive outflow (jet) connected to HR 8119, but possibly also a separate, closer object. In any case, OU4 is one of the largest and most unusual nebula structures discovered so far.
| IMAGE DATA | |
|---|---|
| Object | Sh2-129 and OU4 – Fledermaus- and Riesenkalmar-Nebula |
| Distance | approx. 2300 light years |
| Date | 12. & 13.10.2025 |
| Exposure | RGB each 23x 120sec., Halpha 47x 300sec. & OIII 151x 300sec. - Total approx. 18.8h |
| Mount | Skywatcher EQ6-R Pro |
| Telescope | Askar 120APO with 0.8x Reducer |
| Camera | ZWO ASI 2600mm with ZWO HA, OIII & LRGB Filter |
| Guiding | Zwo Asi OAG with ZWO Asi 290mm Mini & Asiair |
| Software | AsiAir, Astropixel Processor, Pixinsight, Photoshop CC, NoiseXterminator, Star X Terminator, BlurXterminator, Nik Collection 7 |