M46
NGC 2437, NGC 2438
47’ x 31’ | 0.3”/px | 9500 × 6300 px
Puppis
RA 07h 41m Dec -14° 50’ | 0°
Messier 46 (also known as M46 or NGC 2437) is a rich open star cluster located in the constellation Puppis, approximately 5,500 light-years from Earth. Discovered by French astronomer Charles Messier in 1771, the cluster contains several hundred stars and spans about 30 light-years in diameter. Estimated to be around 300 million years old, M46 is notable for its density and relatively high population of bright, young stars. One of its most intriguing features is the presence of a planetary nebula, NGC 2438.
source: ChatGPT
Inside M46, there is a small planetary nebula, named NGC 2438, with a diameter of about 2 arcmin. It was discovered by William Herschel on 19 March 1786. The smallest of the three stars visible in the middle of the nebula is the actual central star that ionises the surrounding layers of gas and makes them emit bright light. especially in the Ha and OIII bands. For long it has been a matter of debate whether NGC 2438 was positioned before or behind M46. Only in 2020, data from the GAIA satellite confirmed that the distance to NGC 2438 is 2360 lightyears, positioning it about halfway between Earth and M46.
Source: Atlas der Planetarischen Nebel
Data Acquisition
Data was collected over 7 nights, from February until April, mainly under full moon conditions, using a 14” reflector telescope with full-frame camera at the remote observatory in Spain. Data was gathered using standrad LRGB filters. A total of about 7 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 |
|---|---|---|---|---|---|---|---|
| 20250209 | 94 | 42 | 90 | 16.0 | 5 | 0 | 0h 00m |
| 20250213 | 97 | 52 | 55 | 18.0 | 6 | 23 | 1h 09m |
| 20250214 | 93 | 60 | 50 | 19.4 | 9 | 7 | 0h 21m |
| 20250216 | 81 | 77 | 70 | 20.4 | 9 | 37 | 1h 51m |
| 20250315 | 98 | 75 | 65 | 19.1 | 2 | 47 | 2h 21m |
| 20250316 | 92 | 84 | 75 | 19.0 | 7 | 9 | 0h 27m |
| 20250407 | 80 | 43 | 50 | 18.2 | 8 | 16 | 0h 48m |
| Total | 139 | 6h 57m |
| Frames | Bin | Gain | Exp.(s) | Frames | Exposure |
|---|---|---|---|---|---|
| Lum | 1 | 0 | 180 | 74 | 3h 42m |
| Red | 1 | 0 | 180 | 20 | 1h 00m |
| Green | 1 | 0 | 180 | 20 | 1h 00m |
| Blue | 1 | 0 | 180 | 25 | 1h 15m |
| Total | 139 | 6h 57m |
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” LRGB 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, CosmicPhotons 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.
To bring out as much detail in the planetary nebula as possible, a slightly different workflow was applied than is normal for star clusters. Stars were extracted from the luminance channel and stretched separately using SetiAstro’s StarStretch. Separately, the nebula was stretched carefully using several steps of GHS and HT. Now the stars were put back in to create a normal luminance image. For the RGB image stars were not removed. GHS stretching in the colour mode prevented the colours to be washed out. GHS can have a bit of a weird effect on stars by creating a bit of a pinpoint effect. For the RGB image this was not too much of a problem. First of all some pinned star centers were smoothened during the convolution phase. Secondly, the luminance channel would bring in regular star shape again.
The image was shot using regular LRGB broadband filters. The nebula emits specifically in Ha and OIII. The respective red and blue colours did come through very well in broadband, so for this purpose it was not necessary to image in narrowband. The nebula was not the main purpose of this image, but should one wish to extract more detail out of the nebula, a narrowband HOO palette would be a good alternative.
The rest of the processing followed a standard processing workflow.
Asteroid 1998 SG36
During processing, a fast-moving star-like object crossed the frames on 15 March 2025. It was fast enough to create little streaks on each 180s exposure. But slow enough to quietly move across the image over several hours. I had seen something similar a few years back when imaging M74. At the time, a friend at my local astronomy club was able to identify the asteroid as 10724 CarolRaymond, and Carol, the person whom the asteroid was named after, even responded to the blogpost that I published on the topic. So how to find out the identity of this object?
A fast-moving star-like object crossed the frames on 15 March 2025
‘What’s in my image’ did not recognise it.
My first attempt was to use the ‘What’s in my image’ script from SetiAstro. But unfortunately it did not recognise it. Then I tried the asteroid overlap function in ASTAP, but it did not find anything either. Then I stumbled over a thread on CloudyNights where someone mentioned Tycho Tracker. This is software focused on identifying satellites, but it also can do a great job with asteroids. So I bought the license, installed it, watched some tutorials and after filling in a couple of settings, I was ready to start the search. I loaded 10 files that had the object in it, calibrated and aligned them in Tycho, and then pressed the button ‘Fast Tracker’. Within a few seconds the software had identified 101 objects that apparently had shown some kind of dynamic behaviour between the frames. The software attaches a confidence factor the results, and only one had confidence ‘high’. The Fast Tracker Results panel now can find two types of searches, one on satellites and one on asteroids. First I tried satellites, but that did not identify any of the objects. Then I tried File > Match Asteroids/Comets, and the high confidence hit was identified as asteroid 1998 SG36. I was really amazed by the results! This process is so simple! Loading a bunch of files, click to have them analysed, click to search for a match and boom, there’s the answer! Those hunting for artificial satellites probably know about this already, but for anyone else, I can highly recommend checking this software out if you see anything moving in your files and wonder what it is.
Tycho quickly found the object
It then searched for matching artificial satellites and asteroids/comets and identified the object as asteroid 1998 SG36
Asteroid 1998 SG36 is a so-called Near Earth Asteroid (NEA). NEA’s have orbits that get pretty close to the Earth’s orbit. This particular one will remain at least 0.12 AU away from the Earth’s orbit, so there is no chance of this ever hitting us, but in astronomical terms, that is still pretty close. 1998 SG36 has a diameter of about 2.2km, which is larger than 99% of asteroids. It orbits around the sun with a speed of 23.2 km/s, which results in a full orbit every 2.11 years. The asteroid rotates around its axis every 3.57h.
Processing workflow (click to enlarge)
This image has been published on Astrobin.
