The Night Sky - Episode 15

THE BUTTERFLY NEBULA

This is episode 15 in my series on our night sky.

The Sadr region, sometimes referred to as the Gamma Cygni Nebula or Butterfly Nebula, is a captivating emission nebula found in the constellation Cygnus. Its common name, the Sadr region, derives from its most prominent star, Sadr (Gamma Cygni). Officially cataloged as IC 1318, this nebula showcases a fascinating interplay of gases, creating a celestial canvas worthy of admiration.

The Butterfly Nebula (IC 1318) spans a considerable area in the sky, roughly covering about 100 light-years across. Its brightness varies across different wavelengths of light, with certain areas shining more prominently than others. This nebula is classified as an emission nebula because the gases in this region emit light of various wavelengths when ionized by nearby stars.

Situated at an approximate distance of 4,900 light-years away from Earth, IC 1318 resides within the Milky Way galaxy. Positioned along the Cygnus Rift, this nebula is nestled in the rich star fields of the northern galactic plane. Its formation can be attributed to the activity within massive molecular clouds, where the gravitational collapse of these clouds initiates the birth of new stars. These stars, in turn, release intense radiation and stellar winds, sculpting the surrounding gases into magnificent structures.

Locating the Butterfly Nebula in the Cygnus Constellation

Cygnus, the swan constellation, hosts the mesmerizing IC 1318. Positioned in the northern hemisphere's summer skies, Cygnus spreads its wings across the Milky Way. Its proximity to the galactic plane makes it an area teeming with celestial wonders, making it a popular target for astronomers and astrophotographers.

The Butterfly Nebula is located at the heart of the Cygnus constellation, drawing attention with its intricate nebulous formations.

Near the Butterfly Nebula lies a network of other intriguing nebulae and significant stars. The North America and Pelican Nebulae (NGC 7000 and IC 5070), the Crescent Nebula (NGC 6888), and the Veil Nebula Complex (Sh-2 103) are some of the notable nebulae sharing the celestial space with IC 1318. Additionally, this region of space boasts a plethora of remarkable stars. From the visually striking double star Albireo to the luminous Deneb, Cygnus offers a range of stellar objects worth exploring and capturing through telescopes and astrophotography equipment.

Sadr: The Crown Jewel of Cygnus

Central to IC 1318 is the brilliant star Sadr, also known as Gamma Cygni (γ Cyg). Sadr is a prominent, luminous star located at the heart of the nebula. Its name comes from the Arabic word “sadr” for “chest”. In fact, it can be found at the chest of Cygnus, the swan constellation.

Classified as a yellow-white supergiant, Sadr is more than 33,000 times brighter than our sun but relatively young at only 12 million years. While the star appears to be at the center of the Butterfly Nebula, this is only true from our point of view here on Earth. In reality, this stellar giant is much closer to us (1,800 lightyears) than the nebula itself. However, its visual juxtaposition with the nebula creates a stunning spectacle and provides a focal point for astrophotographers aiming to capture IC 1318.

True Colours and Simulated Beauty: Understanding Narrowband Imaging

Astrophotography, the art of capturing celestial objects, offers a glimpse into the mesmerizing depths of the cosmos. When exploring nebulae like IC 1318, photographers often encounter a choice between true colour imaging or narrowband imaging.

In pursuit of true colour representation, astrophotographers aim to capture celestial targets in a manner that reflects the actual wavelengths of light emitted by these distant phenomena. However, this endeavor poses challenges due to various factors, including atmospheric interference, light pollution, imaging equipment sensitivity, and the limitations of human vision. When photographing nebulae like IC 1318 in their true colours, the primary challenge arises from the predominance of light emitted by specific gases. Hydrogen-alpha (H-alpha), for instance, emits a deep red hue that completely swamps all other wavelengths due to the abundance of the gas in the universe.

To overcome the challenges of capturing true colours amidst these complexities, astrophotographers utilize narrowband imaging techniques. This method involves using specific filters that isolate light emission of specific wavelengths. For instance, sulfur (SII), hydrogen-alpha (Ha), and doubly ionized oxygen (OIII) emit light at different wavelengths. Combining and assigning these emissions to the RGB (Red, Green, Blue) channels results in a visually striking and enhanced representation of the nebula's structure and details.

Narrowband imaging techniques allow photographers to highlight intricate structures and subtle details within nebulae that might be otherwise challenging to capture in true colors. It enhances the contrast between different gases, unveiling the complex interplay of elements and offering a more visually dramatic portrayal of celestial objects.

While narrowband imaging techniques yield breathtaking images that captivate audiences, it's crucial to recognize the distinction between artistic representation and scientific accuracy in astrophotography. Simulated images, though visually stunning, may not accurately represent the colors visible to the human eye or the true distribution of gases within the nebula.

Both approaches - true colour and narrowband imaging - offer unique insights into the awe-inspiring beauty of celestial objects like IC 1318. Embracing the artistry and technical aspects of capturing these cosmic marvels enriches the experience, encouraging a deeper appreciation for the intricacies of our universe.

The Butterfly Nebula (IC 1318) presents an excellent opportunity for budding amateur astrophotographers to delve into deep-space imaging. With its striking visual appeal and proximity to recognizable stars, capturing the Butterfly Nebula in the Sadr region offers an exciting challenge. Utilizing basic astrophotography equipment and techniques, enthusiasts can attempt to capture the intricate details of this celestial marvel, honing their skills and fostering a deeper appreciation for the wonders of the cosmos.

Check out some other nebulae I have captured.

Capture details

Camera: Astro-modified Canon 80D
Lens: Sigma 100-400mm f/5-6.3 DG OS HSM
Focal length: 400mm (equivalent to 640mm full-frame)
f-Ratio: 6.3
ISO: 800

Number of exposures: 313 total
- 159*180s with Astronomik H-Alpha filter
- 154*180s with Optolong L-Enhance filter
Total integration time: ~15 hours over 4 sessions
Calibration frames: 30 darks, 30 flats, 30 bias for each session

Mount: SkyWatcher Star Adventurer
Guide camera: ZWO 120mm mini
Guide scope: ZWO Mini Guide scope
Capture control: ZWO ASIAir Pro
Dew control: CooWoo dew heater

Sky quality: Bortle 5
Moon phase: Various from 0% to 90%

Processing: PixInsight, Photoshop

View episode 14 in this series here

All episodes in this series