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Thread: Object of the Week December 18, 2016: NGC 2024, The Flame Nebula

  1. #1
    Member RolandosCY's Avatar
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    Object of the Week December 18, 2016: NGC 2024, The Flame Nebula

    Object of the Week December 18, 2016: NGC 2024, The Flame Nebula

    NGC2024
    Orion
    Diffuse Nebula
    RA 05 41' 54"
    DEC -01 51; 00"
    Mag: -
    Dimensions: 30x30 arcminutes

    The area around Alnitak, the easternmost star of Orion’s belt, must surely rank as one of the most exquisite deep sky areas of the entire heaven. Nebulae abound (this is the third OOTW from this area!), and the biggest and brightest by far is NGC 2024, best known as the “Flame Nebula” (also known as the “Tank Tracks nebula, Libs Nebula, and other names). The Flame is large, relatively bright, has many interesting features, has endless challenges, and – most importantly – it is available to the vast majority of observers worldwide, being located only one degree south of the celestial equator. Yet, it is not an object that features often in observing lists, being overshadowed both by the better known attractions of the Great Celestial Hunter, such as the Great nebula of Orion (M42), but also by its proximity to the very bright star Alnitak, which makes observing the nebula a challenge.

    Zeta2hrsUnprocPS1J1acdcJ1a.jpg
    The Zeta Orionis region as photographed by the author

    The Flame Nebula is mainly composed of hydrogen gas, and it is one of the most spectacular H-II regions in the whole Orion B Molecular Complex. Massive star formation is taking place behind the dense clouds of hydrogen and associated dust. These clouds are so thick and dense that few of the new-born stars can be detected in these clouds. There is a star cluster in the nebula’s center that can be detected in infrared, with more than 90 members identified. At the same time, no particular star or stars have been verified as responsible for lighting the nebula. Although Alnitak would seem to be a candidate, it is not, for it is located less than 800 light years away, while the Flame’s distance has been estimated at 1,300 light years (which gives it a real diameter of around 12 light years). It is likely that the Flame gets its illumination from several nearby B-type stars.

    With a detectable diameter of slightly more than 30 arc-minutes (about the same as the full Moon), the Flame Nebula is large. At the same time though, the large diameter spreads the light significantly, thus NGC 2024 suffers from low surface brightness, making it a challenge to observe visually. It can be readily detected even in small instruments, and under dark skies it is fair play for 10x50 binoculars, appearing as a fan-shaped soft glow touching the northeast side of Alnitak (you can confirm it’s not glare by the bright star by moving it around in the field – the fan-shaped glow remains fixed relative to the star).

    With telescopes, things improve dramatically, especially if Alnitak is kept out of the field, or if a narrowband filter is used. Using a Lumicon UHC and a 13mm Ethos eyepiece with my 18-inch dob, a great amount of detail could be seen. The nebula appears to consist of two connected main parts, separated by a rift of darkness with arms, reminiscent of either a strange black cross, or of a ghostly black image appearing through deep fog. In addition, two dark patches appear near the “head” of the ghost figure, which though do not seem to directly correlate with any of the dark features visible in photographs of the Flame. On the night of this observation I spent almost two hours on this nebula, and the dark patches were always visible. The brightness of the nebula varies quite a bit, but appeared to be more pronounced on the northern flanks of the “ghost” image. Some faint stars do dit parts of the nebula. By removing the UHC filter, most features of the nebula are still visible, except for the two dark patches! Also, without a filter Alnitak’s blazing brightness (especially in 18”) does hinder the observation.

    NGC2024A1.jpgZetaFlameBW.jpg
    The Flame as seen through an 18" dob, along with a similarly oriented photograph for comparison

    Using a 4.7-inch f5 achromat the Flame Nebula is better seen with lower magnifications, which help to concentrate the Nebula’s feeble light, and again a UHC filter gives it a tremendous boost. The dark rift is again the most pronounced feature, though at this lower magnification and with the less light of only five inches, the nebula appears to be split in two distinct areas, and the two black patches I observed with the 18” were not detectable. I tried using higher magnification to tease out more details, but the low surface brightness of the Flame did not really help. Using a low magnification (such as 46x) gave me the added benefit of enjoying NGC 2024 as the brightest feature among the nebulous zoo that is found around Alnitak. The Flame Nebula dominates the northern half of the field, while the roundish nebulus patch of NGC 2023 can be seen a similar distance to the south of Alnitak, with the much fainter IC435 barely detectable near it. And of course, to the southeast of Alnitak, the faint nebulous streamer of IC434 runs to a fading end in the darkness, with a triangular notch missing from it near its center – the Horsehead Nebula. A wonderful view of heavenly wonders! Using the five-inch under my skies without a UHC filter I could still detect the Flame Nebula and its rift with direct vision, albeit with much lower contrast, while NGC 2023 was also readily detectable. The flowing nebulosity of IC434 was only visible with averted vision, and the Horsehead was at best suspected.

    Zeta2hrsUnprocPS1J1acdcJ1RFV1BWlabels.jpgZeta5sketch1a.jpg
    The Flame and the Zeta Orionis region through a 4.7" refractor, along with a similarly oriented B&W photo, labelling the various nebulosities visible.

    With both scopes the Lumicon UHC gave me the best results in observing the Flame Nebula, while the H-Beta was second best. I did not like the view using my OIII filters, actually the filterless views were better.

    One of the best views of the Flame Nebula was through my Takahashi 22x60 binoculars. The Nebula was quite distinct, and the black rift was readily visible even at the low power of 22x. Has anybody tried the Flame with a bino-viewer? Using both eyes on this nebula could be quite rewarding.

    So, many things to try on this easy to find nebula during the cold nights of winter (or warm nights of summer if you live in the southern hemisphere). Has anyone else observed the two dark patches? Are there more details that I missed?

    So, next time you are out turn your scope to Orion, “warm up” your eyes with the Flame Nebula, and…

    Give it a Go and Let us Know!
    The Darker the Better!
    -------------------------
    18" f4.5 Obsession Classic #1934
    10" f5 Skyatcher Dob
    152mm f5.9 Teleskop Service
    Takahashi FS128
    SkyWatcher 120 f5
    Takahashi FS102
    Takahashi FSQ106N
    SkyWatcher ED80 Pro
    SkyWatcher ED72 Evostar
    Televue Naglers and Ethos

  2. #2
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    I can contribute a younger sketching result from La Palma with a 20-inch.

    20", 132x, no filter, NELM 7m+, Seeing V (bad)
    NGC2024.jpg

    Nearly 15 years ago I sketched the region from one of the best places in Middle Europe - the Gornergrat at 10300ft. The goal was to detect B 33 with the 20x125 binocular without filter and it was possible. NGC 2024 was also in the 3° field.

    20x125, no filter, 3° field, NELM 7m+
    NGC2024_IC434.jpg
    Clear Skies, uwe
    http://www.deepsky-visuell.de
    Germany

    27" f/4,2

  3. #3
    Member Howard B's Avatar
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    This is a terrific object that I need to concentrate on soon! I only have a sketch where 2024 is secondary to the Horsehead Nebula, but here it is anyway:

    N2024_WidefieldwithB33_crop.jpg N2024_WidefieldwithB33_cropinvert.jpg

    I used an h-beta filter because I was concentrating on the Horsehead Nebula, so 2024 isn't highlighted as well as it would be with an OIII or NPB filter - or with no filter at all. I didn't give 2024 nearly as much time in this sketch as the Horsehead area either. The seeing was exceptionally steady during this sketch though - note that Alnitak is a beautiful double. On the other hand, the SQM was no better than 21.00 so I'm really looking forward to sketching this area is a much darker sky.
    Howard
    30-inch f/2.7 alt-az Newtonian
    https://sites.google.com/site/howardbanichhomepage/
    https://sites.google.com/site/sprays...pemirrors/home
    Contributing Editor, Sky & Telescope magazine

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