Ptolomey’s Cluster, M7 (NGC 6475, The Scorpion’s Tail) (Paul Lloyd)

Celestial hemisphere: Southern · Constellation: Scorpius (Sco) · Contains: B287 · HD162285 · HD162287 · HD162305 · HD162306 · HD162349 · HD162374 · HD162391 · HD162393 · HD162416 · HD162456 · HD162457 · HD162496 · HD162513 · HD162514 · HD162515 · HD162542 · HD162576 · HD162586 · HD162587 · HD162588 · HD162611 · HD162631 · HD162679 · HD162680 · HD162725 · HD162745 · HD162804 · HD162817 · HD162818 · And 18 more.

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Ptolomey’s Cluster, M7 (NGC 6475, The Scorpion’s Tail)

Ptolemy, the Greek-Roman mathematician and astronomer, recorded this object in his famous
Almagest as entry #567 in 130CE. One has to admire this as this open star cluster rises only
a short distance above his horizon in mid-Summer, and he had no optical aid. He described it
as a “nebula following the sting of Scorpius”.

It can be seen with the naked eye just North of the Scorpion’s “stinger”. It comprises some 80
stars with magnitudes between 6 and 10. These are mainly white/blue-white in colour, with
one exception (lower SW corner) being a yellow G8-class star. It is approx. 25 ly in diameter,
and lies 980 ly away. It is one of the most prominent open clusters in the sky, and is the most
southerly Messier object. It is believed to be about 220 Myo and has a mass about 735 times
that of the Sun. It is currently approaching us.

Telescope: William Optics Redcat71 refractor, f=350mm
Camera: ZWO ASI183MC Pro, 60 x 120 sec, no filter
Bortle 3-4 sky, moonless (before moonrise)
Field of View: approx. 1º 00’ x 1º 25’
Image processed and prepared in PixInsight and Photoshop Elements

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Status	Advanced success
Started	...
Astrometry.net job	8453733
PixInsight job	Z7X98JNBDP0EI7T2PUZSST1A1LXXP9PW
PixInsight queue size	n/a
PixInsight stage	TASK_LOG

RA (center)	17h54m02s.35
RA (top/left)	17h56m34s.77
RA (top/right)	17h51m36s.81
RA (bottom/right)	17h51m29s.56
RA (bottom/left)	17h56m29s.24

Dec (center)	-34°47′06″.8
Dec (top/left)	-34°04′03″.1
Dec (top/right)	-34°03′09″.6
Dec (bottom/right)	-35°30′24″.1
Dec (bottom/left)	-35°30′56″.8

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Ptolomey’s Cluster, M7 (NGC 6475, The Scorpion’s Tail)

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Ptolomey’s Cluster, M7 (NGC 6475, The Scorpion’s Tail)

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