MESSIER 7 AKA PTOLEM    Y OPEN CLUSTER

 OPEN CLUSTER IN THE CONSTELLATION OF SCORPIUS (THE SCORPION)

(Image centred at: ra 17h:55m / dec -34º 47')

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AUGUST 2026, Observatorio Cielos Albertnos, Buenos Aires, Argentina

DATA

TYPE: Galaxy Group

APPARENT DIAMETER: 6 arc minutes for the Galaxy Trio Group

APPARENT MAGNITUDE (V): 12.6 12,0 & 11.6 respectivelly

DISTANCE: 190 Million light years

IMAGE INFORMATION

INSTRUMENT: Orion Optics UK 6" Newtonian with Ultra Grade Optics working at f 4.5

CAMERA: QHY 183 Mono Camera

MOUNT: SKY WATCHER NEQ6 Guided off axis with QHY 5II Mono Camera 

FILTERS: Antlia LRGB Set 

SKY CONDITIONS: Bortle 3 to 4 skies

OBJECT DESCRIPTION AND IMAGE SESSION

M7 is also known as the Ptolemy's Cluster after Greek astronomer Claudius Ptolemaeus mention by 130 AD. M7 is one of the brightest cluster of the sky. It can be seen even from urban cities and also a good target for binoculars and small telescopes. From my backyard in good nights and with some effort it can be seen with the naked eye. The cluster contain some 80 stars with a magnitude range from 7 to 12. It is quite close from the centre of our Milky Way therefore the background field full of stars. M7 with its declination -34 º 49 is the southern object of the Messier list.

MESSIER 7 AKA PTOLOMENY CLUSTER

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 OPEN CLUSTER IN SCORPIUS

Image Plate Solver script version 5.6.2

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Referentiation matrix (world[ra,dec] = matrix * image[x,y]):

+1.89371346e-04 +7.40604000e-05 -6.61358160e-01

-7.40838867e-05 +1.89279884e-04 -1.43290842e-01

WCS transformation ....... Linear

Projection ............... Gnomonic

Projection origin ........ [2772.010903 1841.992803] px -> [RA: 17 53 39.964 Dec: -34 44 40.48]

Resolution ............... 0.732 arcsec/px

Rotation ................. -158.619 deg

Reference system ......... ICRS

Observation start time ... 2026-08-09 05:36:05 UTC

Observation end time ..... 2026-08-09 05:39:05 UTC

Geodetic coordinates ..... 58 31 05 W 34 29 19 S 50 m

Focal distance ........... 676.39 mm

Pixel size ............... 2.40 um

Field of view ............ 1d 7' 37.5" x 44' 56.2"

Image center ............. RA: 17 53 39.963 Dec: -34 44 40.47

Image bounds:

top-left .............. RA: 17 50 26.473 Dec: -34 53 06.74

top-right ............. RA: 17 55 34.204 Dec: -35 17 51.50

bottom-left ........... RA: 17 51 47.244 Dec: -34 11 22.86

bottom-right .......... RA: 17 56 52.783 Dec: -34 35 55.14