Astrophotography: The North America & Pelican Nebulae
The Night Sky - Episode 13
THE NORTH AMERICA AND PELICAN NEBULAE
This is episode 13 in my series on our night sky.
Nebulae, those ethereal clouds of interstellar dust and gases, paint the night sky with their cosmic artistry. Among these celestial wonders are the North America Nebula (NGC 7000) and the Pelican Nebula (IC 5070), named for their distinct shapes reminiscent of their earthly counterparts.
The North America Nebula
The North America Nebula (NGC 7000), sprawling across an area of approximately 50 light-years, is a notably bright and expansive emission nebula. Its radiant glow owes itself to the ionization of hydrogen gas by nearby young, hot stars. At an estimated age of 1 to 3 million years, this nebula lies about 1,600 light-years away from Earth in the constellation Cygnus. Its formation, sculpted by the energetic emissions of nearby stars, creates an intricate tapestry of gases and dust, a testament to the ongoing processes of stellar birth and death within our galaxy.
The Pelican Nebula
Adjacent to the North America Nebula, the Pelican Nebula (IC 5070), also an emission nebula, stands as another intriguing celestial spectacle. Slightly smaller than its neighbour, spanning approximately 10 light-years, the Pelican Nebula emanates a delicate luminosity amidst the cosmic darkness. It shares a similar age and distance, about 1,800 light-years away in Cygnus. Both nebulae formed from the colossal forces of young, massive stars, whose intense radiation and stellar winds shape the surrounding materials into these magnificent structures.
The Cygnus Constellation
To locate the two nebulae in the night sky, we must first locate the Cygnus constellation and within that, the star Deneb.
Cygnus, the celestial swan of ancient mythology, is a prominent constellation gracing the northern hemisphere's summer skies.
The tail of Cygnus is marked by Deneb, a radiant supergiant star, one of the three stars forming the illustrious Summer Triangle. With a luminosity that outshines many others in the night sky, Deneb is a beacon of the celestial realm, captivating observers with its brilliance. This stellar giant, located around 2,600 light-years away, adds a dazzling touch to the constellation, inviting observers to gaze at this cosmic swan.
The North America and Pelican nebulae are located to the “east” of Deneb.
Additionally, Cygnus hosts an array of other captivating deep-space objects. The Veil Nebula Complex is a supernova remnant from a massive stellar explosion thousands of years ago. The Crescent Nebula is a magnificent emission nebula that is actively being shaped by a massive hot star at its core.
“2MASS J205551.25+435224.6”: The Ionising Star
Emission nebulae like the North America Nebula (NGC 7000) and the Pelican Nebula (IC 5070) give off no light of their own. They are visible because the radiation from nearby stars blasts the gases in the nebulae, ionizing them and setting them aglow. For a long time, astronomers were unsure which star was responsible for ionizing these two nebulae. In 1922, Edwin Hubble, the famed astrophysicist, proposed that Deneb was the ionizing star. However, detailed measurements of both nebulae’s spectra established that at 8,500K, Deneb was not hot enough to ionize these massive regions of gas. It wasn’t until 2004 that Fernando Comerón and Anna Pasquali discovered a star catalogued as 2MASS J205551.25+435224.6 to be the ionizing star.
Comerón and Pasquali have written a fascinating and fairly easy-to-follow article detailing this discovery. It’s worth a read.
Light Pollution Filters to Improve SNR
Astrophotography involves capturing extremely faint light reaching Earth from deep space objects. With the increase in urbanization, light pollution at night is a real problem for astrophotography. Natural and artificial sources of light pollution wash out the night sky and make it very hard to capture the wonders of the cosmos.
Enter narrowband filters.
Narrowband filters selectively allow the transmission of specific wavelengths of light effectively suppressing the influence of artificial and natural sources of light pollution. For this project, I used the Optolong L-Enhance filter. Its ability to selectively allow only the transmission of wavelengths corresponding to Hydrogen (H-alpha and H-beta) and doubly ionized Oxygen (OIII), proved invaluable under light-polluted skies. This selective filtration allows astrophotographers to capture targeted wavelengths emitted by celestial objects while mitigating the overwhelming impact of city lights and other sources of light pollution, resulting in clearer and more detailed astrophotographic images.
Light transmission curve of the Optolong L-Enhance filter. It is designed to allow the transmission of Hα (656.3 nm), Hβ (486.1 nm) and OIII (500.7 nm and 495.9 nm) wavelengths while suppressing all other wavelengths.
The precision of narrowband filters in isolating specific wavelengths not only enhances the signal-to-noise ratio (SNR) but also improves contrast, allowing for a clearer view of nebular structures amidst light-polluted skies. In essence, these filters serve as a shield against the encroachment of artificial light, empowering astrophotographers to reveal the hidden beauty of the night sky from even the most light-polluted locations.
As we marvel at the North America Nebula and Pelican Nebula, their intricate details and captivating colours, we are reminded of our universe's sheer magnitude and beauty. The night sky holds a treasure trove of celestial wonders waiting to be explored. Grab a telescope, step outside, and immerse yourself in the cosmic canvas, where each twinkling star tells a story of grandeur and mystery.
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: 300mm (equivalent to 480mm full-frame)
f-Ratio: 6.3
ISO: 800
Number of exposures: 182 total
- 12*240s with Optolong L-Enhance filter
- 170*120s with Optolong L-Enhance filter
Total integration time: ~6.5 hours over 2 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: SvBony dew heater
Sky quality: Bortle 3 and Bortle 5
Moon phase: Various from 0% to 95%
Processing: PixInsight, Photoshop