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There is some hesitation about the use of NGC numbers to identify the Monkey Head Nebula. One of the most reliable ones, the SIMBAD system, assigns NGC 2174 to the nebula and NGC 2175 to the open cluster that lies inside the nebula. This is an emission nebula which, like most others, forms new stars at an accelerated rate. Actually, most of the star-like dots that can be seen in this area are YSOs (Young Stellar Objects, or stars in the act of being formed) or massive O and B stars having been formed short ago. Jessy Jose et al., in 2013, determined that there are at least 577 YSOs in this nebula and that the average age of these YSOs is only 500,000 years. The stars are between 1 and 3 million years old. Some authors consider that there are several separated open clusters in this nebula and not only one. This is based in the measured movements of the stars in each cluster.
Additional Information
Object
Name(s): NGC 2174/5. Sh2-252. The Monkey Head Nebula
Type: Emission Nebula
RA: 06h 09m 41s
Dec: +20º 29’ 52”
Constellation: Orion
Size (arcmin): 30×30 arcmin
Magnitude: +7.6
Distance: 7.600 ly
Image
Date: 2021-03-01 to 2022-03-26
Location: Curiosity2 Observatory, New Mexico Skies, Mayhill, NM, USA
Size (arcmin): 31×31 arcmin
Telescope: 24” (61 cm) f/6.5 Reflector
Camera: FLI PL16803 (4096x4096pix)
Guiding: Astrodon MonsterMOAG off-axis guider
Total exposure: 21 hours (Ha: 8h; OIII: 6h; SII: 4h; RGB: 3h)
Processing: CCDStack, PixInsight (one step) and Photoshop CC 2023