Roger Samworth

DSOs 02-03/10/2019

Posted by Roger Samworth

Last night looked pretty promising and it was the last chance to get out before going away for 2 weeks +. However, once outside the sky seemed very hazy, making it impossible to go hunting for very faint DSO. So had to be satisfied with a few brighter ones. I thought it might be nice to look at the M31 companions, M32 and M110 for a change. So here they are. Not very exciting! You can only see the central sections.

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Clusters seemed appropriate in the circumstances, so here is M34, as I hadn’t imaged it before. Probably on account of its size. This image is in fact a mosaic of four.

After that the sky had cleared a little so I went for M1, the “Crab” nebula, as I hadn’t looked at that for a while.

 

 

M32 and M110 were from 20 10-sec frames, M34 was from 20 1.2-sec frames and M1 from 40 10-sec frames.

 

Roger’s further processing of my M101 image from last night

Posted by Andrew Thornett

I often get a similar effect (green images) with the PD when I am doing an extreme stretch. I put it down to a cheap camera! I reduce it by stretching the luminance only and then trim it using “curves” on the individual colours. However, the GIMP light pollution routine you posted does a pretty good job. What do you think of this? I simply used repair or clone on the main galaxy despeckled layer before setting its mode to subtract.

Process used in detail:

  1. Duplicate image
  2. Despeckle top layer – set radius to max, black to 0 white to max uncheck recursive and adaptive.
  3. Despeckle layer now has blob over M101. Get rid of it using clone or repair
  4. Set mode of despeckle layer to subtract
  5. Merge down
  6. QED

Roger

Hunter’s Moon?

Posted by Roger Samworth

Being unable to sleep last night, I was greeted in the early hours by seeing the Moon lurking in the Hyades, hiding behind Taurus’s head, presumably to protect itself by being clobbered by Orion the Hunter.

Here it is, taken with my Sony DSC-HX60 compact camera with a bit of GIMP magic to combine images of different exposures to avoid the Moon’s glare washing out the stars:

And here is the Moon’s hiding place in the Hyades:

Alexander’s dark band

Posted by Roger Samworth

Now here is a name for an effect that I have observed and been puzzled about!

Alexander’s dark band – – Alexander of Aphrodisias first described the effect with double rainbows in 200 AD and it now carries his name.
Light rays undergoing a single reflection in raindrops form the primary rainbow or brighten the sky inside it. Rays reflected twice are deviated to form the secondary bow or brighten the sky outside.

Raindrops along lines of sight between the two bows cannot send light to your eye and so the sky is darker there.

You can see the effect in this image I posted a year or so ago.

 

Read more at https://www.atoptics.co.uk/rainbows/adband.htm or https://en.wikipedia.org/wiki/Alexander%27s_band