Sunday 22 June 2014

The pleasure and pain of astronomy

Hello all,

There is one thing about astronomy that is most challenging - the weather!

We are left totally to the mercy of the vagary and fickleness of the weather.

I have been wanting to do a sketch of the Moon for the last fortnight.  Before the full Moon, persistent overcast conditions curtailed any chance.  The four days around the full Moon were fine, but this phase though very challenging coincided with work commitments.  This last week has been an exercise in sheer frustration - the days have been beautiful, clear ones, with little cloud.  Yet each and every single night has seen cloud roll in either right on sunset, or at the very time I've planned to set up a telescope.  This morning I got up at 3am, being confident that this wretched cloud would cease to be problematic as cloud had not appeared when I turned in for the night.  At 3am, I looked out the window, and cloud was solid horizon to horizon!!!  AAHHH, so frustrating!

Today I am presenting one of my most satisfying sketches, that of the giant globular cluster Omega Centauri.

Globular clusters present real challenges to illustrate.  More orthodox illustration techniques struggle to overcome the texture of the paper, and lack the depth of density that is visible.  Even more challenging with large globulars using large apertures of telescope is the sheer complexity of form and numbers of stars, and not extending the sketch far enough to give a surrounding context.

But, if a good technique is found, a sketch can produce an image that is not just vivid, but can reveal detail that is burnt out in photographs.  With Omega Centauri, this burnt out feature is one of its signature markings "The Eye".  Each globular cluster has what I like to describe as 'a unique fingerprint' - unique markings, strings of stars, patterns depth, and details.  Omega's Eye is a coincidence of line of sight where a hollow appears formed by an apparent lack of bight stars in this spot at its core.  Long exposure photographs reveal that there is no real lack of stars, and is purely a coincidence.

One thing about that makes Omega Centauri unique among the globular clusters that orbit the Milky Way is it if far from being 'normal' globular cluster.  Omega is considered to be the remnant core of a smaller galaxy swallowed up by the Milky Way long, long ago.  Evidence of this is more than its immense size.  Its very size makes it too big to be normal globular.  The only way that such a large number of stars can be stably maintained so tightly is if a black hole is at its core.  Further evidence that Omega is not a typical globular cluster is the variation in age of the component stars.  Typical globular clusters are made up of very old stars, evidenced by the absence of heavier elements in the spectrum of these stars.  The stars of Omega vary in age, as the spectrum of the stars reveal heavier elements that are only formed from later stellar evolution.

This particular sketch was done using my 17.5" push-pull dobsonian from my home in Sydney.

Object:  Omega Centauri, NGC 5139
Telescope:  17.5" push-pull dobsonian
Gear:  16mm Unitro Konig, 125X
Location:  Sydney, Australia
Date:  24th March, 2012
Media:  White pastel, charcoal and white ink on A4 size black paper
Duration:  approx. 2.5hrs.

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