Flying Bat and Squid Nebula

Sh2-129, also known as the Flying Bat Nebula, is a faint emission nebula in the constellation Cepheus, near the more famous IC 1396 nebula. It is particularly well known in astrophotography because it also contains the much fainter Ou4, the Squid Nebula, which appears as a blue, bipolar structure within the red hydrogen emission.

Characteristics and Physical Description
• Sh2-129 is dominated by hydrogen-alpha (Ha) emission, giving it a distinct red appearance in narrowband imagery.
• The nebula is sometimes referred to as the “Flying Bat Nebula” due to its wing-like appearance.
• It is located near RA 21h 09m 40s and Dec +59° 58’ 20’’ (J2000), making it accessible for northern hemisphere observers.
• The field of view to fully capture both Sh2-129 and Ou4 is roughly 2 to 4 degrees, requiring a wide-field imaging setup.

Notable Features: Ou4 (The Squid Nebula)
• Inside Sh2-129 lies the remarkable and extremely faint Squid Nebula (Ou4), discovered in 2011 by amateur astronomer Nicolas Outters.
• Ou4 is characterized by strong OIII (doubly ionized oxygen) emission and requires long exposures with an OIII filter to capture.
• Recent studies suggest it may be a bipolar outflow associated with the triple star system HR 8119, located at Sh2-129’s center.

Imaging Considerations
• Capturing the full extent of both nebulae is challenging due to their faintness, especially Ou4, necessitating long integration times and narrowband OIII filters for best results.
• Sh2-129 itself makes for a good narrowband target in late summer and autumn for northern observers, being visible most of the night.

Astrophysical Significance
• Sh2-129 has been cataloged since at least the 1950s as part of the Sharpless catalog of HII regions.
• The discovery and study of Ou4 have added to the mystery, providing a rare example of possible star-driven bipolar outflows within a well-known HII region.

Sh2-129 is therefore of special interest to both deep-sky imagers and astrophysicists due to its complex structure and the embedded, recently discovered Squid Nebula.