Caldwell 39
NGC2392, Lion Nebula
9’ x 6’ | 0.3”/px | 1800 x 1200px
Gemini
RA 7h 29m Dec +20° 55’ | 180°
Caldwell 39, also known as NGC2392, is a bipolar double-shell planetary nebula (PN). It was discovered by astronomer William Herschel in 1787. The formation resembles a person's head surrounded by a parka hood. It is surrounded by gas that composed the outer layers of a Sun-like star. The visible inner filaments are ejected by a strong wind of particles from the central star. The outer disk contains unusual, light-year-long filaments.NGC 2392 lies about 6500 light-years away, and is visible with a small telescope in the constellation of Gemini. At the center of NGC 2392, there is an O-type star (designated HD 59088) with a spectral type of O(H)6f. On 11 August 2020, the IAU Working Group on Star Names (WGSN), NASA/IPAC Extragalactic Database (NED), and SIMBAD Astronomical Database (CDS) discontinued use of three nicknames that were perceived as offensive – "Eskimo Nebula", "Clown Face Nebula", and "Clownface Nebula" – and strongly recommended the nebula be referred to by its NGC designation in further publications.
source: Wikipedia
Data Acquisition
Data was collected over 8 nights from mid-January to mid-February 2025 using a 14” reflector telescope with full-frame camera at the remote observatory in Spain. It was gathered in narrowband using Ha, OIII and SII filters. For proper star colours, additional data was collected using short RGB exposures. A total of about 25 hours of data was combined to create the final image.
Location Remote hosting facility IC Astronomy in Oria, Spain (37°N 2°W)
| Sessions | Moon% | Moon° | Hum% | SQM | T°C | Frames | Exposure |
|---|---|---|---|---|---|---|---|
| 20250119 | 65 | 78 | 50 | 21.2 | 2 | 25 | 4h 10m |
| 20250131 | 9 | 130 | 75 | 21.5 | 1 | 39 | 6h 30m |
| 20250202 | 27 | 101 | 65 | 21.2 | 3 | 8 | 1h 20m |
| 20250204 | 49 | 72 | 63 | 20.8 | 4 | 24 | 4h 00m |
| 20250205 | 60 | 58 | 70 | 20.4 | 0 | 36 | 6h 00m |
| 20250206 | 71 | 44 | 65 | 19.8 | 1 | 10 | 1h 40m |
| 20250213 | 97 | 49 | 55 | 18.0 | 6 | 2 | 0h 20m |
| 20250214 | 93 | 62 | 50 | 19.4 | 9 | 30 | 1h 30m |
| Total | 25h 30m |
| Frames | Bin | Gain | Exp(s) | Frames | Exposure |
|---|---|---|---|---|---|
| Ha | 1 | 2750 | 600 | 48 | 8h 00m |
| OIII | 1 | 2750 | 600 | 48 | 8h 00m |
| SII | 1 | 2750 | 600 | 48 | 8h 00m |
| Red | 1 | 0 | 180 | 10 | 0h 30m |
| Green | 1 | 0 | 180 | 10 | 0h 30m |
| Blue | 1 | 0 | 180 | 10 | 0h 30m |
| Total | 174 | 25h 30m |
Equipment
Telescope
Mount
Camera
Filters
Guiding
Accessoires
Software
Planewave CDK14 (2563mm @ f/7.2), Optec Gemini Rotating focuser
10Micron GM2000HPS, custom pier
Moravian C3-61000 Pro (full frame), cooled to -10 ºC
Chroma 2” Ha, OIII, SII (3nm) and R, G, B unmounted, Moravian filterwheel L, 7-position
Unguided
Compulab Tensor I-22, Dragonfly, Pegasus Ultimate Powerbox v2
Voyager Advanced, Viking, Mountwizzard4, Astroplanner, PixInsight 1.9.3
Processing
All processing was done in Pixsinsight unless stated otherwise. Default features were enhanced using scripts and tools from RC-Astro, SetiAstro, GraXpert and others. Images were calibrated using 50 Darks, 50 Flats, and 50 Flat-Darks, registered and integrated using WeightedBatchPreProcessing (WBPP). The processing workflow diagram below outlines the steps taken to create the final image.
StarXTerminator struggled to differentiate between the nebula and stars, mistakenly treating most of the nebula as a star. To avoid this, a mask matching the nebula's size was created using the GAME script. With this mask, SXT extracted the stars while leaving the nebula (including the central star) untouched in the starless image. The individual narrow-band channels were adjusted using HistogramTransformation, stretching the image until the center of the nebula reached a brightness of about 0.8, making it clearly visible.
Normally, stretching can cause the nebula to appear as a single large star, but this manual method allowed for detailed visibility without losing highlight detail. The SII signal was weak and needed more stretching. Therefore this manual approach resulted in an unbalanced color, which was fixed with the NarrowbandNormalization script. The strong OIII signal was reduced to create a teal color instead of bright blue, while the weak SII signal was boosted. To balance colours further, SCNR was applied.
The nebula is small, often appearing more like a star with standard stretching methods. To highlight the nebula while keeping some context, the original 60MP image was cropped to a 2MP version, offering a 9' x 6' view. Despite this, the nebula still appears small, so a close-up crop from the center is provided. You may also want to view the full-resolution image.
Close-up of the planetary nebula Caldwell 39
According to regular conventions, the image here is upside down, with north pointing to the bottom of the image. However, I like the very bright star HD59087 much better in the bottom part of the image than the top part.
The rest of the processing followed the standard processing workflow.
Processing workflow (click to enlarge)
This image has been published on Astrobin and received Top Pick status.
