M68
NGC 4590
44’ x 29’ | 0.3”/px | 4800 × 3200 px
Hydra
RA 12h 39m Dec -26° 12’ | 180°
Messier 68, also known as NGC 4590, is a globular cluster located in the southern constellation Hydra. Discovered by the French astronomer Charles Messier in 1780, this dense stellar system lies approximately 33,600 light-years from Earth and contains hundreds of thousands of ancient stars bound together by gravity. As one of the more remote globular clusters in the Messier Catalogue, M68 stands out for its rich, symmetrical structure and relatively low metallicity, indicating that its stars formed early in the universe's history. Its age is estimated to be around 10-12 billion years. M68 spans about 106 light-years in diameter.
source: DeepSeek
Data Acquisition
Data was collected over 6 nights during April and May 2025, using a 14” reflector telescope with full-frame camera at the remote observatory in Spain. Data was gathered using standard LRGB filters. A total of approximately 11 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 |
|---|---|---|---|---|---|---|---|
| 20250408 | 88 | 51 | 55 | 18.0 | 10 | 58 | 2h 54m |
| 20250511 | 100 | 27 | 55 | 19.0 | 10 | 44 | 2h 12m |
| 20250515 | 89 | 69 | 70 | 20.0 | 10 | 25 | 1h 15m |
| 20250516 | 82 | 81 | 60 | 21.3 | 10 | 44 | 2h 12m |
| 20250517 | 73 | 92 | 55 | 21.0 | 10 | 43 | 2h 09m |
| 20250518 | 64 | 104 | 55 | 21.6 | 12 | 8 | 0h 24m |
| Total | 222 | 11h 06m |
| Frames | Bin | Gain | Exp.(s) | Frames | Exposure |
|---|---|---|---|---|---|
| Lum | 1 | 0 | 180 | 109 | 5h 27m |
| Red | 1 | 0 | 180 | 33 | 1h 39m |
| Green | 1 | 0 | 180 | 40 | 2h 00m |
| Blue | 1 | 0 | 180 | 40 | 2h 00m |
| Total | 222 | 11h 06m |
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.
Green and Purple RR Lyrae variable stars
Sometimes when collecting data at different dates, individual stars can get some strange colours, like green or purple. These stars are often so-called RR Lyrae variable stars. The unique property of these variable stars is that they fluctuate in brightness very quickly. Their period is often less then one or up to a few days and fluctuate up to a full magnitude in brightness. So the brightness of such stars captured with a particular colour filter may be much higher one day vs the other. This can happen with each filter, but for the red and the blue filter, this would just show up as more or less red or blue, and would go unnoticed. If it happens with the green filter though, the colour would fluctuate between green and its opposite colour purple. Green if the green filter happens to pick up that star in a high brightness moment, purple if the star is in a low brightness moment. So RR Lyrae variable stars can show as all kinds of colours, but the ones that stand out are the green and the purple ones.
RR Lyrae stars can be identified using the SetiAstro script ‘What’s in my image’. Just load the image in the script, (1) click Advanced Search and (2) select Object Type RR*, with description ‘Variable Star of RR Lyrae type’. (3) Click ‘Confirm Selections’. Shift-click and drag in the image to draw a circle around the area where you suspect the RR Lyrae stars. Then (4) click ‘Query Simbad Defined Region. A list of objects that are found within the search area will now populate under the image. (5) Click the star that you’re interested in, and (6) the associated line-item will highlight. There are a ton of objects that can be identified this way, so always nice to experiment with.
In this particular image 38 RR Lyrae variable stars were identified. In the below image, just four are labeled using the ‘What’s in my image’ script.
The ‘What’s in my image’ script from SetiAstro is a great tool to explore unknown objects in your photographs. Here it is used to identify RR Lyrae variable stars
Four of the RR Lyrae variable stars in M68 identified.
The rest of the editing followed a standard processing workflow.
Processing workflow (click to enlarge)
This image has been published on Astrobin.
