M69
NGC 6637
22’ x 15’ | 0.3”/px | 4500 × 3000 px | full resolution
Sagittarius
RA 18h 31m Dec -32° 20’ | 0°
Messier 69, also known as NGC 6637, is a globular cluster in the southern constellation of Sagittarius. The cluster was discovered by Charles Messier on August 31, 1780, the same night he discovered M70. At the time, he was searching for an object described by Nicolas-Louis de Lacaille in 1751–2 and thought he had rediscovered it, but it is unclear if Lacaille actually described M69. This cluster is about 28,700 light-years away from Earth and 5,200 ly from the Galactic Center, with a spatial radius of 45 light-years. It is a relatively metal-rich globular cluster that is a likely member of the galactic bulge population. It has a mass of 200,000 M☉. It is a close neighbour of its analog M70 – possibly only 1,800 light-years separates the two.
source: Wikipedia
Data Acquisition
Data was collected over 8 nights in August 2025, using a 14” reflector telescope with full-frame camera at the remote observatory in Spain. Data was gathered using standard RGB filters. A total of approximately 7 hours of data was finally combined to create the final image.
Location Remote hosting facility IC Astronomy in Oria, Spain (37°N 2°W)
Sessions
Frames
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” RGB 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.
M69 is the second lowest Messier object on the horizon with a declination of -32°, only exceeded by M7, which declination is -34°. The consequence of these low altitudes is that weather conditions need to be very good to image a reasonably sharp image. During the eight sessions when images were shot for this target, conditions varied significantly. Originally 10 hours of data was collected, but during integration a total of 37 frames were discarded as they did not meet the specified criteria. For example, on August 26 a total of 16 frames were shot, but all were rejected during WBPP processing.
M69 is not a very large cluster, so the final image was cropped to approximately half the size in each dimension to have a nicely balance composition in the final image. The original field of view can still be seen as one of the images at the top of this page. Also the full resolution version is the original image.
The rest of the processing workflow followed regular procedures.
Processing workflow (click to enlarge)
This image has been published on Astrobin.
