M79
M79 - Click here for full resolution
Messier 79, also known as NGC1904, is a globular cluster located in the constellation Lepus, the Hare, approximately 42,000 light-years from Earth. It was discovered by French astronomer Pierre Méchain in 1780 and later included in Charles Messier's catalog. M79 contains an estimated 150,000 to 200,000 stars packed into a region about 118 light-years in diameter. The cluster has a bright, compact core and an overall apparent magnitude of 7.7, making it relatively easy to spot with binoculars or small telescopes under dark skies. One of the most intriguing aspects of M79 is its unusual location. Unlike most globular clusters, which are concentrated toward the Galactic Center of the Milky Way, M79 lies in the opposite direction, toward the Galactic anticenter. This has led astronomers to hypothesize that M79 may not have originated in the Milky Way but could instead be associated with the Canis Major Dwarf Galaxy, a satellite galaxy currently being absorbed by the Milky Way. This extragalactic origin makes M79 an important object for studying the dynamics of galactic interactions and the accretion of smaller galaxies into larger ones. M79 is also notable for its population of variable stars, including RR Lyrae stars, which are used as standard candles to measure astronomical distances. The cluster's age is estimated to be around 11.7 billion years.
source: DeepSeek
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NGC1904
n.a.
Globular Cluster
Lepus
05h 24m 11s
-24° 31.4′
42.000 ly
7.7
29 December
28º S
Conditions
M79 is best visible during Winter. Its declination however of -24° makes it difficult to image from Europe. This image was taken at the remote observatory at IC Astronomy in Oria , Spain. From there, the maximum altitude reached is only 28° in late December. M79 was photographed over 5 nights during mid-December and mid-January when the moon was >75% illuminated.
Equipment
The default rig at the observatory was used. The core of this rig is a Planewave CDK-14 telescope on a 10Micron GM2000 mount, coupled to a Moravian C3-61000 Pro full-frame camera. The RoboTarget module in Voyager Advanced automated the process to find optimal time-slots during astronomical night.
Telescope
Mount
Camera
Filters
Guiding
Accessoires
Software
Planewave CDK14, Optec Gemini Rotating focuser
10Micron GM2000HPS, custom pier
Moravian C3-61000 Pro, cooled to -10 ºC
Chroma 2” Luminance, Red, Green and Blue unmounted, Moravian filterwheel L, 7-position
Unguided
Compulab Tensor I-22, Windows 11, Dragonfly, Pegasus Ultimate Powerbox v2
Voyager Advanced, Viking, Mountwizzard4, Astroplanner, PixInsight 1.9.2
Imaging
M79 is a typical broadband object, that is not very critical to conditions of moon interference and were shot when moon illumination was >75%. To minimise moon the effect of the moon light all images, also the R,G and B images, were shot as 3 min exposures. The total exposure was 11.9h. With the object being so low at the horizon, image quality was not great, with large FWHM values in general.
Resolution (original)
Focal length
Pixel size
Resolution
Field of View (original)
Rotation
Image center
5500 × 3667 px (20.2 MP)
2585 mm @ f/7.3
3.8 µm
0.30 arcsec/px
37' x 25'
-0.489°
RA: 05h 24m 11.024s
Dec: -24° 31’ 30.25”
Processing
All images were calibrated using Darks (50), Flats (50) and Flat-Darks (50), registered and integrated using the WeightedBatchPreProcessing (WBPP) in PixInsight. All further processing was done in PixInsight, including the use of scripts and tools developed by RC-Astro, SetiAstro, GraXpert, and others. For a step-by-step description of the processing techniques applied, see process flow below.
As a general practise I make flats only once in a while. For this image, the original set of flats did not correct some of the dust motes very well in the luminance channel. So I took a new set of flats, and although they were doing better, still a few of the dust particles had moved. I could probably have gone back to each individual frame and check which of the two sets of flats would work best, but instead I decided to move on with the best integration, and cloned out some of the dust motes in the background of a starless version of the luminance.
M79 is a small cluster with a bright core. It’s low altitude from the site where this image was taken, made it difficult to retrieve the amount of detail one can otherwise get from a globular cluster. In order to maximise the amount of detail in the core, while at the same time showing all the stars in the dimmer part of the cluster, an HDR technique was applied. There are multiple options for HDR in PixInsight. In this case I chose to create an HDR version of the luminance using HDRMultiScaleTransform. This HDR version was blended with the original in a 50/50 way using ImageBlend.
When the Lum is treated so differently than the RGB image, it is important to end up with two images that have somewhat equal star-size. If not, the star colours may come out very strange. So during the stretching phase and later brightness adjustments, several times star sizes were compared and even adjusted if need be.
Towards the end of processing, some green was left in the image. In order to not affect any star colours anymore at this point, SCNR was applied on a masked version of the image, targeting only the background signal.
Processing workflow (click to enlarge)
This image has been published on Astrobin
