Monday, 31 March 2014

Southern Cross

The Southern Cross is the simplest Southern Hemisphere constellation to find.  It was used as a rallying point by rebelling miners in Victoria in 1854 and the Eureka stockade flag continues to be used as a symbol of protest.  I have the flag used in the 1976 protests against Governor-General Sir John Kerr (but that is another story).

I have a new lens for my camera - a 12" Dobsonian and I am learning to take high magnification shots. Tonight I practiced on the Southern Cross and environs.
Mimosa - Pulsating variable 278 Light Years B0.5III - Bottom Southern Cross

My camera is attached to the Dobsonian using  a T Ring (this replaces the Camera lens and acts as a solid frame for the telescopic attachments).  I then use two Barlow attachments to give me sufficient focus depth.  All focusing then took place using telescope controls, which with the Canon 7D became a trial and error process. 

Lens configuration
12" Dobsonian

I then turned to the sky.

Southern Cross

Below and to the right of the bottom star in the Southern Cross - Mimosa - is a small open cluster - NGC 4755 - C94.  My first couple of shots - using ISO 6400 at 25 seconds produced star trails - so I cut the exposure time to 0.5 second.

Open Cluster NGC 4755 - C94
The resulting photograph captures the stars and the colors - but does not do justice to the fine beauty of the cluster.  The brighter stars have burnt through and even at 0.5 seconds there is still a sign of trailing or perhaps camera shake.  Will have to practice more :)

I then turned to the stars making up the Southern Cross itself.  Mimosa is at the top of this post.

Gacrux - 88 Light Years M4III - Left Southern Cross 

Eta Crux 228 Light Years K3/K4 III  - Top Right Southern Cross

Acrux - Double Star 320 Light Years - B0.51V  - Right Southern Cross

During the shoot, the temperature dropped and the telescope began to frost over (I am about 1km high out here).  I was using trigger trap and an iPhone to take the shots - I started with lots of charge but the phone drained very quickly and I had to complete with the inbuilt time delay.

Peter Quinton
1 April 2014

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