Ou4 & Sh2-129
Key Astrophysical Data
Catalog Designations
Ou4 (Giant Squid), Sh2-129 (Flying Bat)
Position in the Sky
Cepheus (RA 21h 11.8m / Dec +59° 59′)
Apparent Size
150′ × 150′ (Absolutely massive widefield area)
Apparent Magnitude
Extremely faint (Ou4 requires extreme exposure)
Discovery Date
1950s (Sh2-129) / 2011 (Ou4 by N. Outters)
Object Type
H II Emission Region & Bipolar Outflow
Distance from Earth
~2,300 Light Years
Physical Size
Ou4 spans ~50 Light Years across
Power Source
HR 8119 (Triple star system)
Object Overview & Facts
A Recent, Incredible Discovery: While the red emission nebula Sh2-129 (The Flying Bat) has been cataloged since the 1950s by Stewart Sharpless, its hidden companion remained completely invisible to science for decades. It wasn't until June 2011 that French amateur astrophotographer Nicolas Outters, while shooting an extremely deep exposure of the region through a narrow Oxygen-III filter, noticed a faint, bizarre shape. This led to the discovery of Ou4, now famously known as the Giant Squid Nebula.
The Bipolar Outflow (Ou4): The Giant Squid is not a standard emission nebula. It is a massive bipolar outflow—a colossal pair of jets composed primarily of doubly ionized oxygen (OIII). The jets are being blasted outward in opposite directions at immense speeds. The true nature of Ou4 was initially debated; some thought it might be a planetary nebula (the death throes of a sun-like star), but modern consensus suggests it is an outflow driven by the massive, young stars at its heart.
The Engine (HR 8119): At the very center of the Squid's body lies the triple star system HR 8119. This system contains massive, hot, young stars whose fierce stellar winds and ultraviolet radiation are responsible for both ionizing the vast red hydrogen gas of the Flying Bat and propelling the blue-green jets of the Squid. The outflow from this system has carved the spectacular, elongated shape of Ou4 over hundreds of thousands of years.
Immense Scale: The physical size of this complex is staggering. Because it sits roughly 2,300 light-years from Earth, its apparent size of 2.5 degrees on the sky means the entire Flying Bat complex is over 100 light-years across. The Giant Squid alone stretches approximately 50 light-years from tip to tip, making it one of the largest bipolar outflows ever discovered in our galaxy.
Astrophotography Guide: Ou4 is widely considered an "endgame" target for deep sky astrophotographers. The Hydrogen-alpha signal of the Flying Bat is relatively straightforward to capture, but the OIII signal of the Squid is punishingly faint. Imagers must use narrow bandpasses (usually 3nm) and routinely collect 30, 40, or even 60+ hours of exposure time to properly reveal the body and tentacles of the Squid against the background space.
Deep Sky Objects Size Comparison Laboratory
Interactive Scaling Explanation: This panel acts as a dynamic comparator of angular sizes in the night sky. All selected objects are rendered exactly over each other from a common center, allowing an immediate, direct comparison. The Full Moon (diameter 31') serves as a permanent baseline reference.
Cosmic Time Machine: Squid & Bat vs. Earth's History
The Photon Arrives: Right now, the light captured in this photograph is ending its roughly 2,300-year journey through deep space, hitting your camera's digital sensor. Move the slider back in time to see what humanity was doing while these precise photons were rushing through the void.
Cosmic Scale: Distance Map Laboratory
Dynamic Linear Scaling & Manipulation: This view builds an interactive, deep-space linear cosmic coordinate system. When swapping objects, the line auto-calculates its limit. Leave only near targets (Pleiades, Orion) checked to reveal detailed stellar gaps inside our galactic neighborhood. Turn on remote galaxies (Andromeda, Whirlpool) to watch the Milky Way bundle together on the left margin. Use your mouse wheel to zoom in/out and drag to pan across space to explore cluttered zones!