NGC 1261 - aka CADWELL 87

GLOBULAR CLUSTER IN HOROLOGIUM (THE PENDULUM CLOCK)

(ra: 03h 12' 16"/ dec -55º 12')

CLICK THE IMAGE FOR A HIGH RESOLUTION VIEW

ANNOTATED IMAGE 75% RESOLUTION

December 2025, Home Backyard in Martinez, Buenos Aires, Argentina

DATA

TYPE: Globular Cluster

Visual Brightness: 8.63

APPARENT DIAMETER: 12,9 arc minutes

DISTANCE: 53000 light years

IMAGE INFORMATION

SCOPE: 6" ORION OPTICS UK (Ultra Grade Optics) w/Sky Watcher Coma Corrector (0.9x) working at at f4.5

CAMERA: QHY 183 MONO

MOUNT: VIXEN GPDX w/Sky Watcher EQ5 motors set - OAG with QHY 5II Mono

FILTERS:  OPTOLONG LRGB Set

SKY CONDITIONS: Urban Skies, Bortle 9 - full Moon

EXPOSURES: LRGB (45,45,45,45) - all channels bin 1x1

OBJECT DESCRIPTION AND IMAGE SESSION

NGC 1261 (also known as Caldwell 87) is a globular cluster of stars in the southern constellation of Horologium. It was first discovered by Scottish astronomer James Dunlop in 1826 from Parramatta Australia. The cluster is located at a distance of 59000 light-years from the Galactic Center. It is about 10.24 billion years old with 341,000 times the mass of the Sun.

In the past, astronomers thought that all the stars in a globular cluster had similar ages and similar chemical abundances. However, recent studies suggest that this might not be true. It seems as though many globular clusters contain stars with varying chemical abundances, suggesting the stars are different ages. Hubble’s observations of Caldwell 87 have allowed astronomers to investigate this further.

NGC 1261 does not display the normal indications of core collapse, but evidence suggests it may have instead passed through a post core-collapse bounce state within the past two billion years. The central luminosity density is kind of low for a globular cluster, despite this, it has a Shapley–Sawyer Concentration Class of II, indicating a dense central concentration.

The are still same faint small galaxies visible in the image annotated, some other though were wiped out by the bortle 9 sky of my home backyard.

NGC 1261 - aka CADWELL 87- ANNOTATED IMAGE

GLOBULAR CLUSTER IN HOROLOGIUM (THE PENDULUM CLOCK)

(ra: 03h 12' 16"/ dec -55º 12')