COLLINDER 140

OPEN CLUSTER IN CANIS MAJOR (THE GREAT DOG)

(ra: 07h 24' 53"/ dec -31º 52')

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

DATA

TYPE: Open Cluster

Visual Brightness: 3.5

APPARENT DIAMETER: 60 arc minutes

DISTANCE: 1200 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: SKYWATCHER NEQ6, OAG with QHY 5II Mono

FILTERS:  OPTOLONG LRGB Set

SKY CONDITIONS: Urban Skies. Bortle 9

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

OBJECT DESCRIPTION AND IMAGE SESSION

Collinder 140 is a nearby open cluster of stars in the constellation Canis Major. It was first catalogued in 1751 by the French astronomer Nicolas Louis de Lacaille from the Cape of Good Hope, who described it as a "nebulous star cluster" although there are no nebula around this cluster.  It was catalogued again by the Swedish astronomer Per Collinder in 1931. Collinder 140 is a young extended cluster were its members are quite disperse. Some studies indicate that it may be instead a mere grouping of stars that formed together. The cluster has a density of 0.21 solar masses per cubic parsec; roughly double the density of stars near the Sun. It is about 20 million years old, and may have been created from the same interstellar cloud that formed NGC 2516 and NGC 2547.

The field of view of the QHY 183 plus the OOUK 685 mm almost cover its extension. Collinder 140 is one of the few objects which can be seen at the naked eye from my light polluted backyard in Martinez.