Butterfly Cluster, M6

This beautiful cluster was riding high in the clear night sky, almost at the zenith. It was the first image of five objects which I obtained during an evening out in the field with my friends from Macarthur Astronomical Society.

The M6 cluster is about 94 million years old. It needs some considerable imagination to see a butterfly shape but if you begin with the two almost symmetrically curved rows of small stars arranged in a v-shape – the antennae – then perhaps you might be off to a good start.

Most of the stars in the cluster are hot B-type stars but the bright orange star is BM Scorpii, an orange supergiant (mag.6) which has exhausted its hydrogen and swollen in size as it converts helium into heavier elements. It lies in front of the cluster at about 790 light years distance – about half the distance to the cluster. Despite being a supergiant, it is a K2 star which is cooler than our  G2 Sun.

There was great excitement amongst our hardy group of astronomers at the news that a bright comet P/2008 Y12 (SOHO) had arrived in the sky.

However, I had other targets in mind – and I’m glad I did, because my friends spent much of the evening searching for it, to no avail. It clearly was much dimmer than the predicted 10th magnitude, which is not uncommon.

After seventeen minutes of this first image, my mount stopped tracking, so here it is – a seventeen minute image of the Butterfly Cluster.

Unfortunately, I had hardware/software/gearware problems which resulted in imaging for shorter durations than I intended but taking a couple more objects (five instead of three) – with a resultant reduction in quality.

The other images will no doubt follow.

Object Details:

Designation: Messier 6, M6, Butterfly Cluster.
Constellation: Scorpius
Visual magnitude:  +4.2
Apparent size:  20′ x 20′
Diameter:  9.2 light years.
Distance:  1,600 light years.
Altitude during exposure:  82° above W. horizon.

My previous image of M6.

Technical stuff:


Exposure:  12 x  86.2 sec = 17.25 min.
Gain: 230
Date:  2019-08-24
Location:  semi-dark rural.
Conditions:  clear
Moon: no.


Image acquisition:  SharpCap.
Method: Live stacked.
Darks: no.
Image post-processing:  GIMP.
Cropping:   no.
Sky:  0.22 e/pixel/s .


Telescope: SkyWatcher Esprit  Type: 120ED triplet refractor
Focal: 840 mm F/7 Mount: SkyWatcher EQ6-R Pro
Camera: ZWO ASI 071 MC Pro
Type: CMOS 28.4mm 16 Mpx
Optical aids: Flattener: Y; filter: N Guiding: No
Polar aligning: QHYCCD PoleMaster Polar Error: 00’ 19”

Geek Log:

[ZWO ASI071MC Pro]
Debayer Preview=On
Output Format=FITS files (*.fits)
Capture Area=4944×3284
Colour Space=RAW16
Hardware Binning=Off
Turbo USB=40
Frame Rate Limit=1 every 4 seconds
Timestamp Frames=Off
White Bal (B)=50
White Bal (R)=53
Cooler Power=37
Target Temperature=-15
Auto Exp Max Gain=300

Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Mono Bin=Off
Anti Dew Heater=Off
Banding Threshold=35
Banding Suppression=0
Apply Flat=None
Subtract Dark=None
#Black Point
Display Black Point=0.0523809523809524
#MidTone Point
Display MidTone Point=0.604761904761905
#White Point
Display White Point=1

Image © Roger Powell


  1. I think I saw something like a butterfly with the left side more defined than the right.

    Then, I thought it might be a side view instead of a front view. Then, I wasn’t sure what I was seeing but the photo is nice.

    Liked by 1 person

    1. Well at least you tried. The two antenna helped me but the wings and body are a bit vague. Whoever configured those stars could have done a better job.
      Thanks for commenting.


  2. I alluded to something similar before, but it is amusing for me to think of M6 as “high in the sky.” It is pretty low in the South sky where I am, for a brief time in the Summer only.

    Great picture.


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