OBSERVER’S CHALLENGE* – February, 2023
by Glenn Chaple
NGC 2024 “Flame Nebula” Emission Nebula in Orion (Magnitude, "7.2 (O'Meara)" Size 30’ X 30’)
Our February Observer’s Challenge, the emission nebula NGC 2024 (the Flame Nebula”) in Orion, tests our visual skills in two ways. A 7th magnitude object, as estimated by Stephen James O’Meara, its light is spread over an area the size of the full moon. Worse yet, the Flame is hidden by the glare from the nearby bright star zeta (ζ) Orionis (Alnitak).
The Flame Nebula was discovered by William Herschel on the night of January 1, 1786. He cataloged it as a Class V object (Very large nebulae) and wrote, “Wonderful black space included in remarkable milky nebulosity, divided in 3 or 4 large patches; cannot take up less than a half degree, but I suppose it to be much more extensive”.
You won’t need its 2000.0 coordinates, RA 5h41m54s and Dec -01o51’0.0” to find the Flame Nebula. It’s just 15 arc-minutes ENE of Alnitak, the most southeasterly of Orion’s three Belt stars. Seeing it visually requires moving Alnitak out of the field of view. Although a large-aperture scope is recommended, the Flame can be seen with small aperture instruments and medium magnifications, especially if skies are transparent and an O-III filter is used. O’Meara has glimpsed it with 7X50 binoculars, suggesting that Alnitak be blocked by a distant rooftop or sharp-edged structure.
Once you’ve (hopefully!) managed to capture the Flame Nebula, it’s time to turn to another challenge - that pesky star Alnitak. At a visual magnitude of +2.0, it’s the brightest spectral class O star in the sky. A hot blue supergiant, it’s 20-30 times more massive than the sun and some 10,000 times more luminous. Alnitak has a visual companion – a blue-white giant of magnitude 3.7 situated some 2.4 arc-seconds to its SSE (Position Angle 166o). The pair may be split with a 3-inch scope and magnifying power of 150X, provided the seeing is steady. A third member, of 9th magnitude, lies 59 arc-seconds to the northeast.
The Flame Nebula is located about 1400 light years away. It has a diameter of approximately 6 light years
NGC 2024 Image
Mario Motta, MD. (ATMoB) “Taken with my 32 inch F6.5 telescope in Gloucester, MA, with ZWO ASI6200 camera. I used Red/Blue/Green filters, but also H alpha as there is some emission in Ha. No significant O3 or S2 emission to be had in NB imaging here. Total of 3 hours imaging in all. Combined and processed in PixInsight, including the new BlurXterminator, giving crisp detail. Field of view is 24x16 arc minutes.”