The OIII Falls - Sh2-91

Image Title: The OIII Falls - Sh2-91

Copyright: Jordi Jofre

Date image was taken: June 19, 2025

Location: Àger, Catalonia

Data Acquisition Method: Personal Telescope Setup

Description and Details: This image captures SH2-91, a faint and filamentary structure located in the constellation Cygnus. It represents a part of an ancient supernova remnant known as G65.3+5.7, believed to be over 20,000 years old and spanning more than 3 degrees across the sky. What we see here is just a thin section of its intricate filament network.

SH2-91 is especially remarkable in the OIII emission line, which reveals a sinuous, glowing arc tracing the shock front where the expanding blast wave from the supernova continues to plow through the interstellar medium. The ionized oxygen, energized by the remnant’s shock, emits strongly in blue-green light, producing the elegant structure reminiscent of a cascading cosmic waterfall—hence the nickname “The OIII Falls.”
Capturing this image has required 19h of exposure in Ha and OIII filters, plus 1.5h of exposure in R, G and B filters for the stars. Total exposure time has been about 40h.
The setup I used was formed by a TS Optics 94mm @ f4,4 and a mono camera ASI 2600MM Pro over an AM5 mount from ZWO

Name: Jordi Jofre

Website or Facebook Profile: https://www.astrobin.com/users/JJofre/