M104 - Sombrero Galaxy

RA: 12hrs 40min 00secs      Dec: -11 37' 00"    Mag: 8.3   Distance: 1500 light years   Constellation: Corvus

The best Easter weekend I can remember for a long time - clear skies at night from Friday to Sunday.  This was an unexpected bonus - M104 never rises very high in our skies and from my vantage point, the glow of Abingdon usually prevents any views of the southern horizon.  I think the trick that enabled me to see the Sombrero was the fact that I was taking much longer than normal to drift align the elevation plane of the telescope - I kept overshooting the correction and having to approach alignment again and again.  I started late because it was Easter Sunday and I was singing Evensong in Oxford.  So, by the time I aligned the scope and selected M104 on the Goto, it was past 11pm.  I think much of the moisture in the air must have reached dew-point, and it's my belief that this clears the fine particulate matter from the air since they act as nucleation centres for condensing water vapour.  Anyway, the unmistakable glow of a galaxy appeared on the DSI and after that, it was a matter of adjusting the black and white points.  I also discovered with this session, that the auto-guide really does work on Envisage, even if you're taking photos with it - it can only compute guidance in between exposures so to make it work better, you turn up the correction gain from the default of 0.5 to anything upwards of 0.80.  

This picture is the stack of 3 exposures, each in turn made up as follows: 47x30 seconds, 24x30, 71x30, making a total exposure time of 71 minutes.  The temperature was 9.8C and there was no wind.  Moon was in its final quarter and didn't rise until much after this session was finished.  Seeing was not great but then it never is in Oxfordshire.  Post-processing was very simple - white point was already saturated in the foreground stars, dark point was reset and mid-tones increased using the curves command in Photoshop.  The image was subjected to 1 pass of Noise-Ninja with the luminance setting turned down to 8 and smoothing and contrast down to 4.  Final filter was Gaussian blur with radius of 1.0.

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