The Night Sky - Episode 17
THE FLAME AND HORSEHEAD NEBULAE
This is episode 17 in my series on our night sky
Amidst the frigid darkness of winter, two of the night sky's most enigmatic and stunning nebulae drift across the southern horizon—the Flame Nebula and the Horsehead Nebula. I have been fascinated with these two nebulae and have tried and failed to photograph these targets over the past three years. This year, after careful planning and with some luck, I finally captured these celestial wonders despite the challenges posed by the limited clear nights and the technical demands of deep-space photography.
The Flame Nebula (yellow to the left) and Horsehead nebulae (red to the right). A total of 96 exposures of 3 minutes each were shot and processed to complete this image.
Image by Achint Thomas
The Flame Nebula (NGC 2024) is primarily an emission nebula, its red and orange hues resulting from ionized hydrogen atoms. It is approximately 1,350 light-years away from Earth and spans about 6 light-years in actual size. Its apparent size in the sky is roughly 30 arcminutes, comparable to the size of the full moon.
The Horsehead Nebula (Barnard 33) is a dark nebula silhouetted against the bright backdrop of a vast region of ionized hydrogen in space. The horsehead portion consists of dense dust, which absorbs the light from the stars and nebulae behind it, creating the iconic horsehead shape. The nebula is slightly farther, at about 1,500 light-years, and smaller, about 3.5 light-years across, with an apparent size of 8 arcminutes. It is also much fainter than the Flame Nebula and requires a dark sky and specialized filters to observe.
Orion: History and Mythology
The Flame and Horsehead Nebulae are located in the constellation of Orion. As one of the most recognizable constellations in the night sky, Orion has been steeped in mythology and history for millennia.
Orion Constellation in the night sky.
Image by Till Credner [image reference]
In Greek mythology, Orion was a giant huntsman of great beauty and strength, who was placed among the stars by Zeus. The stories vary, but one popular version recounts Orion's tragic end, where he was killed by a giant scorpion sent by the Earth goddess Gaia. To honor him, Zeus placed Orion in the sky, eternally fleeing the scorpion, which became the constellation Scorpius.
The mythological significance of Orion extends beyond Greek mythology. In ancient Egypt, the constellation was associated with Osiris, the god of the afterlife, fertility, and the Nile. This connection underscored the Egyptians' deep astronomical knowledge and their belief in the heavens' influence over earthly matters.
In Navajo lore, Orion is known as “The First Slim One” or “First Slender One.” The Navajo associated the constellation with agriculture. When Orion sets at dusk (which happens during May), it signals the start of the planting season.
The stories and interpretations of Orion are as varied as the cultures that tell them, each adding a unique layer to our understanding of this majestic constellation. Whether seen as a mighty hunter, a god of resurrection, or a celestial guardian, Orion's presence in the night sky continues to inspire awe and wonder across generations.
Locating the Two Nebulae
Locating the Flame and Horsehead Nebulae in the night sky is straightforward. But to do so, one must first locate the Orion constellation.
Orion is a winter constellation, named so because it is prominently visible in the night sky during the winter months in the Northern Hemisphere. From late November to early February, Orion rises in the east shortly after sunset and reaches its highest point in the sky around midnight. This makes it an ideal target for stargazing on cold, clear winter nights.
After you have found Orion, look for Orion's Belt, a distinct line of three bright stars: Alnitak, Alnilam, and Mintaka. These stars form the central part of the constellation. Once you have located Orion’s Belt, focus on the easternmost (leftmost) star of the trio, Alnitak. This star is your key reference point for locating the Flame and Horsehead Nebulae.
Location of the Flame and Horsehead nebulae in the constellation of Orion. The nebulae can the found in the region around the left-most belt star Alnitak.
Image by Achint Thomas
The Flame Nebula is situated just to Alnitak's left (east). It appears as a bright, diffused region surrounding the star. With a telescope, especially using a hydrogen-alpha filter, you can see the intricate structure of the nebula, which resembles flickering flames.
The Horsehead Nebula is located just south of Alnitak. Due to its faintness, it is best seen using a telescope equipped with a narrowband filter, such as a hydrogen-alpha filter. The Horsehead Nebula is a dark silhouette against the bright background of the emission nebula IC 434. Look for the distinctive dark shape of the horse’s head protruding into the glowing region.
For the best viewing experience, find a dark-sky location away from city lights. Use a telescope with good aperture and appropriate filters to enhance the visibility of these nebulae.
Other Notable Deep Sky Objects in Orion
Orion is a treasure trove of deep-space objects, each with its own unique characteristics and beauty. The constellation is home to nebulae of various kinds, star clusters, and even some of the brightest stars in the night sky.
A number of deep-space objects can be found in the Orion constellation
Image by Achint Thomas
Rigel
Rigel is the brightest star in Orion and the seventh brightest in the night sky. It is a blue supergiant located about 860 light-years away. Rigel is an extremely luminous star, radiating about 150,000 times the luminosity of the Sun, with a radius about 70 times larger. It is a key reference point in the constellation, serving as the hunter’s right foot, and illuminates the surrounding nebulous regions. Rigel's intense brightness and blue hue make it a striking object for stargazers and a vital component of the stellar landscape in Orion.
Alnitak and the Belt Stars
Alnitak, the brightest star in Orion's Belt, is a blue supergiant located about 1,260 light-years away. Its radius is 20 times larger than our Sun and it shines about 20,000 times brighter. Its intense ultraviolet radiation illuminates the surrounding nebulae, contributing to the spectacular glow of the Flame Nebula. Alnitak, together with Alnilam and Mintaka, forms the belt around Orion’s waist, a striking line that is both a visual delight and a pointer to several other deep-space objects.
Betelgeuse
Betelgeuse, a red supergiant star, is another bright star in the night sky and marks the shoulder of Orion. It is located about 600 light-years away and has a diameter of around 760 times that of the Sun. If this star were in the place of our Sun, its outer shell would reach out to the asteroid belt, engulfing the orbits of Mercury, Venus, Earth and Mars. Betelgeuse is nearing the end of its life and is expected to go supernova within the next 100,000 years—a relatively short time in astronomical terms. When it does, it will likely outshine all other objects in the night sky, potentially even being visible during the day. This impending supernova has made Betelgeuse a subject of intense study and fascination.
Barnard's Loop
Barnard's Loop is a large arc of glowing gas that stretches across much of the constellation Orion. It is thought to be a remnant of a supernova explosion that occurred around two million years ago. The loop is faint but can be captured with long-exposure astrophotography. It envelops several other nebulae, including the Orion Nebula and the Flame Nebula, forming a large part of the Orion Molecular Cloud Complex. Its massive, sweeping arc highlights this region's turbulent history of star formation and supernova activity.
A closeup of Barnard’s Loop and central nebulae in the Orion Constellation
Image by Achint Thomas
Orion Nebula (M42)
The Orion Nebula, also known as M42, is one of the most famous and well-studied nebulae in the night sky. It is located about 1,344 light-years away and is a stellar nursery where new stars are born. Visible to the naked eye as a fuzzy patch, it is best observed through a telescope, revealing a stunning array of colors and intricate structures. The Orion Nebula contains the Trapezium, a young, open cluster of stars that illuminates the surrounding gas and dust. This nebula offers a glimpse into the processes of star formation and is a favorite target for both amateur and professional astronomers.
The Orion Nebula
Image by Achint Thomas
Here is a post on my capture of the Orion Nebula.
Witch Head Nebula (IC 2118)
The Witch Head Nebula, IC 2118, is a reflection nebula located about 900 light-years away. Its name comes from its eerie resemblance to the profile of a witch's head, with the nebulosity primarily reflecting the light of the nearby supergiant star Rigel. This nebula is relatively faint and requires a dark sky and good observing conditions to view. The bluish tint of the Witch Head Nebula is due to the scattering of Rigel's intense blue light by the interstellar dust in the nebula.
Lambda Orionis Cluster (Collinder 69)
The Lambda Orionis Cluster, also known as Collinder 69, is an open star cluster centered around the bright star Lambda Orionis, also known as Meissa. This cluster is about 1,300 light-years away and contains several dozen stars. It is part of the larger Lambda Orionis Ring, a large ring-shaped molecular cloud. The cluster is an excellent target for binoculars or small telescopes and provides a rich field of stars that make for an impressive sight in the constellation Orion.
Each of these deep-space objects and stars contributes to the rich tapestry of the Orion constellation, offering myriad opportunities for observation and discovery. Whether you are a seasoned astronomer or a novice stargazer, the wonders of Orion provide a fascinating glimpse into the complexities and beauty of the universe.
The Capture Process
Astroimaging combines art and science, requiring meticulous planning, specialized equipment, and technical expertise. For this particular image of the Flame and Horsehead Nebulae, I used an astro-modified Canon 80D, a 400mm telephoto lens, a star tracker with auto-guiding, and a dual-narrowband filter. Let’s delve deeper into the specifics capturing such deep-space images.
Astro-Modified Camera
An astro-modified camera is essential for capturing the intricate details of nebulae. The modification involves removing the camera’s infrared filter, which allows more hydrogen-alpha light to reach the sensor. This is crucial because hydrogen-alpha light, emitted by ionized hydrogen gas, makes up a significant portion of the light from nebulae. Without this modification, the nebulae's vibrant colours and fine details would be significantly diminished.
Telephoto Lens
A telephoto lens (in the 300mm-500mm range) provides a good balance between field of view and magnification, making it suitable for capturing both the Flame and Horsehead Nebulae in a single frame. This focal length allows for sufficient detail while still encompassing the vast regions of space these nebulae occupy.
Star Tracker with Auto-Guiding
A star tracker is indispensable for deep-space astrophotography. It compensates for the Earth's rotation, allowing the camera to track the stars precisely over long exposures. Auto-guiding takes this a step further by using a secondary camera, telescope, and guiding software to make minute corrections to the tracker’s movements. This ensures that the stars appear as sharp points rather than streaks, even during long exposure times, which can extend to several minutes per frame.
Dual-Narrowband Filter
Dual-narrowband filters are a game-changer for capturing nebulae from light-polluted skies. They isolate the hydrogen-alpha (Ha) and oxygen-III (OIII) emissions, which are prominent in nebulae while blocking out much of the light pollution. This increases the contrast and detail in the final image, making the nebulae stand out against the background sky.
Light transmission curve of the Optolong L-Enhance filter, a typical dual-narrowband 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.
Astrophotography requires not just advanced equipment but also strategic planning. Given the limited clear nights due to sub-optimal weather conditions, I had to make the most of each night. This meant closely monitoring weather forecasts and being ready to drive hours to a dark sky site to set up and photograph. However, the process is fraught with challenges, from equipment malfunctions to sudden changes in weather. On some nights, clouds would roll in unexpectedly, cutting short the imaging session. Other times, the auto-guiding would need recalibration, costing valuable dark-sky time. Patience and perseverance are key.
Despite the challenges, capturing the Flame and Horsehead Nebulae was an enjoyable experience that helped me feel a strong connection to the vast and intricate universe beyond our planet. I encourage you to explore the Orion constellation and the celestial wonders within its borders. Whether through a telescope or a camera lens, observing the night sky offers a glimpse into the breathtaking complexity and beauty of the cosmos.
Happy stargazing!
Check out some other nebulae I have captured.
Capture details
Camera: Astro-modded Canon 80D
ISO: 800
Lens: Sigma 100-400mm f/5-6.3 DG OS HSM
Focal length: 400mm (equivalent of 640mm full-frame)
f-Ratio: 6.3
Sub-exposure length: 180 seconds
Number of exposures: 96 (with Optolong L-Enhance filter)
Total integration time: 4.8 hours
Calibration frames: 30 darks, 30 flats, 30 dark flats
Mount: SkyWatcher Star Adventurer GTi
Guide camera: ZWO 120mm mini
Guide scope: ZWO Mini Guide scope
Capture control: ZWO ASIAir Pro
Dew control: SvBony dew heater
Field Power: AIMTOM 194Wh Portable Power Station
Sky quality: Bortle 5
Moon phase: 85% to 100%
Processing: PixInsight