NGC 6809, Messier 55 in Sagittarius

NGC 6809, M55, is one of the easiest globular clusters

to resolve.  Located in the constellation Sagittarius,

M55 contains 100 000 stars and

is 17.6 kly from us.

Hover over the picture for an annotated version

Date:  3 July 2022, 25 August 2025, and 7 July 2026

FOV:  approximately 45' × 30'; the angular size of M55 is about 19'

Rotation:  −0.015°

Telescope:  Stellarvue SVX102T + SFFX-1 (737.5mm, f/7)

Guiding:  ZWO ASI120MM mini mono guide camera,

Stellarvue F050G 50mm guide scope

Computer:  ASIair pro Raspberry Pi

Mount:  iOptron CEM40 2022, ZWO AM5 2025

Camera:  ZWO ASI071MC Pro Cooled (-10°C) Color CMOS with gain 240, 2022

ZWO ASI6200MC Pro Cooled (-10°C) Color CMOS with gain 100, 2025

ZWO ASI2600MC Pro Cooled (-10°C) Color CMOS with gain 100, 2026

Pixel size:  4.78 μm, 2022, 3.76 μm, 2025 and 2026

Resolution:  1.337 arcsec/pixel, 2022, 1.054 arcsec/pixel, 2025 and 2026

Filter:  Baader Light Pollution Moonglow filter with IR cut, 2022

Optolong UV/IR, 2025 and 2026

Stacking:  twenty-one 240 second frames Deep Sky Stacker, 2022

twenty-five 240 second frames PixInsight, 2025

twenty-six 300 second frames PixInsight, 2026

Calibration frames: 20 dark, 20 flat, 2022,

20 dark, 20 flat, 20 dark flat, 2025 and 2026

Total Time:  5 hours and 14 minutes

Processing:  Pixinsight – StarAlignment 2020, 2025 and 2026 → linear

MGC, DBE, SPCC, BlurXT, NoiseXT, GHS, HST, MStr, MAS,

PMath MAS + MStr + GHS + HST, Sat, DynCrop/Scale

Location:  Cherry Springs State Park near Coudersport, PA, 2022

Darling Hill Observatory near Vesper, NY, 2025 and 2026