Globular Cluster Caldwell 106

Designation:       NGC 104.
Magnitude: +3.95
Apparent size:50 arc-min.
Diameter:213 light years.
Distance:15,000 light years.
Exposure:15 x 177 sec = 44 minutes.
Field of View:46.6 x 30.8 arcmin. Up is 124° degrees E of N.

One of the two very finest globular clusters, with naked eye visibility in dark skies, 47-Tucanae lies just 18° from the South Celestial Pole, near the Small Magellanic Cloud.

It is mostly about the same size as the Moon but with some sparse outliers extending even further.

Wide Angle Location Image

2012-10-07 Small Magellanic Cloud (centre) and 47-Tucanae (above)
16x8sec ISO1600 f1.4 50mm Black & White Reversed
RP 2012-10-07

With its countless millions of stars, I’ve imaged 47-Tucanae before and it’s one of those beautiful objects which draws me back to it every year to try and improve the image quality.

However, if I recall correctly, this was also one of the occasions when clouds forced a sudden change of plan and a quick choice had to be made on which object to shoot in a different direction before the sky completely disappeared. I chose 47-Tucanae.

Interesting Footnote

The Director of our local observatory, Campbelltown Rotary Observatory, Dr Ragbir Bhatal, has been scanning the skies for potential laser signals from advanced alien civilisations, in a survey called Optical Search for Extra-Terrestrial Intelligence (OSETI)

2009-07-04 – my image of the OSETI Plaque which was placed at the original observatory to record that the location of the first Optical Search for Extra-Terrestrial Intelligence was in Campbelltown, NSW. The whereabouts of the plaque since the re-opening of the Observatory is unknown to me.

Ragbir reportedly keeps a bottle of champagne locked in a cabinet somewhere, to celebrate in the event of him finding and validating an OSETI signal.

In 2008 Ragbir reported the detection of “a laser look-alike” signal coming from a star system in an undisclosed location. However he has since been unable to replicate receipt of the signal and so the champagne remains under lock and key and the trip to Stockholm remains out of reach.

He has since revealed that the star from which he detected the signal was in fact located in the above globular cluster, 47-Tucanae.

Telescope Details

SkyWatcher Esprit 120 mm apochromatic 3-element refractor; 840 mm f/l @ f/7.
Field flattener; Baader L-Booster UHC-S light pollution filter 2458276; 2x Powermate
SkyWatcher EQ6-R Pro mount; ZWO ASI120 guide camera.
Camera: ZWO ASI 071 MC Pro (CMOS 28.4mm 16 Mpx).
Software: PHD2, SharpCap, Gimp.
Observatory location: 34° South.

See annotated image at Astrometry.net

I’m one of the founder members of Macarthur Astronomical Society, Australia. 🙃

The Seven Best Southern Sky Objects


  1. If aliens are anything like us, they frown on shooting lasers into the sky all willy-nilly like for fear of blinding some passing UFO pilot.

    Of course, to them, they are regular flying objects pilots.

    Liked by 2 people

    1. Of course aliens are like us. I’ve seen them in science fiction movies. They breathe air, speak English and generally have two arms and two legs, unless they are Daleks.
      But unlike us, if they exist, they could send targeted powerful laser signals in attempt to catch our attention.

      Liked by 1 person

  2. I hope Dr. Bhatal gets to open his bottle one day for having discovered a signal. Hard work and determination should be rewarded somehow.

    Two nights ago I was looking straight overhead toward Vega and Cygnus. A faint streak of light crossed. I assumed it was a meteor. Then, pointed the scope at Alberio to admire the nice color contrast of A and B in that double. Tomorrow night I want to see the Moon rise with Mars very near.

    Liked by 1 person

    1. He’s thinks outside the square and works to a very low budget. Chances are low, rewards are high….

      With Full Moon gone, I’m hoping for a run of clear nights this cycle. Chances are low, rewards are…..


    1. Thanks, Donna. We have plenty of favourites here in the Southern Hemisphere, it’s hard to know where to start.

      Are you allowing visitors at during the pandemic? Here at MAS we’ve cancelled all public nights.


    1. I’d like to know that too.

      Best case scenario: 15,000 years ago an advanced alien civilisation in a globular cluster orbiting outside the galaxy briefly aimed a powerful laser signal towards our solar system, as part of a programme to send targeted signals to all 400 billion Milky Way star systems. The signal stopped because of alien government budget expenditure cuts; or alternatively it moved on to target another region of the galaxy.

      Worst case scenario: spurious internal reflections in the Schmidt-Cassegrain optics or some form of electromagnetic disturbance in the electronic analysing gear.

      My heart says the former, my head tells me it’s the latter.


      Liked by 1 person

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