The Flying Bat and the Giant Squid

SH2-129: The Flying Bat Nebula

Located in the northern constellation of Cepheus, SH2-129 (nicknamed the "Flying Bat Nebula") is a cloud of ionized hydrogen approximately 1,300 light-years away. This vast celestial object spreads its reddish tendrils across 2.3 degrees of sky, several times the apparent size of the Full Moon.

Its glow comes primarily from hydrogen atoms excited by ultraviolet radiation from surrounding stars, creating the crimson hue characteristic of star-forming regions. Its distinctive morphology gives it a highly pronounced arched appearance, indeed evoking a bat with outstretched wings.

OU4: An Extraordinary Amateur Discovery

The story takes a remarkable turn with the serendipitous discovery of a second nebula nestled within SH2-129. In June 2011, French astrophotographer Nicolas Outters spotted this structure, which he named the "Giant Squid Nebula." The peculiarity of OU4 is that it remains invisible without a specific OIII filter, which isolates the emission line of doubly ionized oxygen around 500 nanometers. This technique revealed this bluish ghost.

Dimensions and Nature of OU4

OU4's dimensions are astounding: with its 50 light-year extension and one-degree angular size, it surpasses all known planetary nebulae in size, occupying twice the lunar diameter in the sky. More distant than SH2-129, it lies at about 2,300 light-years, creating a purely accidental alignment between these two structures.

Its bipolar morphology intrigues astronomers. In these objects, gas ejected by a dying star is often disturbed by nearby stellar companions, creating asymmetric rather than spherical shapes. Researchers believe OU4 represents a flow of material propelled approximately 90,000 years ago by HR 8119, a system of three massive, very hot stars detected at the nebula's core.

A Photographic Challenge

Capturing this stellar duo represents a true technical feat. The extreme faintness of these structures requires dozens of hours of light accumulation, sometimes spread over multiple nights of observation. The final images typically combine data from two complementary filters: one captures the red hydrogen of SH2-129, the other the blue-green oxygen of OU4, producing these striking compositions where the cosmic squid appears to float in a crimson ocean.