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From Summer towards the Winter along the Milky Way


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What Does a Starfield Hide?

I am experimenting with using the multi-spectral feature of StarlightLive to capture wide field images of the sky and also display the H-II regions of the same areas. I would have liked to continue with this thread, where I left an earlier thread near the Pipe nebula area in Southern Ophiuchus https://stargazerslounge.com/topic/265965-from-winter-towards-the-summer-along-the-milky-way/?do=findComment&comment=2912530. But as work didn't allow me to have any astronomy outings during the summer, there will be a gap.

To start as South as I can from latitude 47 at the end of September, I aimed at the Small Sagittarius Star Cloud M24. I am not very knowledgeable about celestial objects and didn't know what to expect. I was surprised by the amount of H-alpha that I saw, in particular behind the star cloud. Here it is. (BTW North is towards the left of the image.)

Small.Sagittarius.Star.Cloud_2016.9.30_19.52.24_crop_85%.jpg

I checked with Astrometry.net and it identified only two Hydrogen nebulae, the well known and obvious IC 1283/84 and IC4701. As I am only in the early stages of experimenting with this real-time RGB+Ha overlap technique, I seriously thought that all the red that seems to protrude from below the star field is just some false positive. A dense area of the Milky Way that the H-alpha filter picks up as a continuum. But then I read more about the Sharpless objects and found a statement that "Sh 2-38, Sh 2-40, Sh 2-41 and Sh 2-42 all appear to be embedded in the Sagittarius OB4 association." So it seems that the entire M24 star cloud is an enormous group of young stars still swimming in the cloud of Hydrogen from which they were born and ionizing it with their UV radiation. According this, the red mat, that we see to extend over the edges of the star cloud, especially in the corner near the black nebulae, is just that gas cloud and has the Sharpless numbers mentioned in the quote.

Here is a version annotated as well as I could. Except that I didn't label Sh 2-38, Sh 2-40, Sh 2-41 and Sh 2-42 as I didn't know which number refers to which part of the Hydrogen cloud and too many numbers would have just over-crowded the image.

Small.Sagittarius.Star.Cloud_2016.9.30_21.26.47_annot_85%.jpg

As said, the technique of making these overlap captures is still in an experimental state. For these captures I didn't stack at all, I just added up the components. I was planning to continue with this same object today using a better lens and stack more frames. But clouds moved in, rain started and I am not likely to be able to return to this object any more times this year. It was already very low with the horizon cutting into the image after 9 pm. The trick that needs more practicing is to prevent the H-alpha exposures from tripping up the natural neutral color balance of the stars. As you see, I was more successful with this on the second capture.  The images were captured with an 85mm camera lens and an SX-825 mono camera. They have been cropped to about 85% size to fit within the posting file size limit and to cut out the obnoxiously bright and blown out Omega Nebula M17.

I apologize for my lack of in-depth knowledge about the objects and the tentative experiemental nature of the captures. But the curtain has just rolled down on this object for the year. I can post whatever I have or wait until next summer. I plan to continue this thread, as time permits, with hopefully better captures of other objects from along the Northern arch of the Milky Way.

Clear Skies!  --Dom

Edited by Dom543
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For comparison, here is a black and white capture of the Small Sagittarius Star Cloud from last summer. It is rotated to have North up and was taken with a better lens.

Milky.Way.Star.Cloud.M24_portrait_2015.8.17_23.21.08.jpg

This is a pure H-alpha capture. It also shows the Hydrogen gas but it doesn't jump out as obviously because of the lack of color. The stars are so tiny and pin point, because this is just their H-alpha component. In H-alpha stars are always nice and tiny.

Clear Skies!  --Dom

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Great piece of work Dom, very interesting region which I shall have a look at on my atlas to familiarise, sadly I cannot see it from my current home, but planning a move soon so fingers crossed for new location.  When you say you didn't stack, but added up the components, how does that work?

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Thank you Rob!

As I said in the post, I am still experimenting with this technique. That's why I didn't get into explaining it in more detail. Things will probably still change. 

If you look at the subscript of the first posted image, you see that it was made of two frames. The two frames were merged using the stacking routine of StarlightLive. I said that it wasn't a stacked image because, in my mind, I reserve the word "stacking" for the action, when exposures of the same object are merged with the purpose of reducing noise and improving image quality.

In the current case the two frames that were merged were very different. They were captures of two different physical layers of the object. The first one was a black and white image of a star field. The second one was a capture of a red extended gaseous nebula. Due to their very different nature, no noise reduction or image quality improvement occurred, when the two frames were merged. 

I hope that this clarifies my usage of words. At least somewhat.

Clear Skies! --Dom

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Here is my latest and definitely the last attempt at the Small Sagittarius Star Cloud for the year. It is taken with a monochrome Ultrastar Sr. (SX-825 with cooling not turned on.)

Small.Sagittarius.Star.Cloud_2016.10.3_20.25.20_85%.jpg

 

I don't know, if it is better than the earlier versions but at least I tried to do what I wanted. Despite of the gloomy forecasts, the night started out clear. Unfortunately, by the time I set up and polar aligned,  clouds moved in and didn't depart before the entire object sunk below the horizon. The grayish stuff on the left side of the image is the effect of these high clouds. Unfortunately they are not just obscuring haze but they are also reflecting the light pollution of the urban area (Seattle).

Anyway, this capture is of a narrower FOV taken with a 135mm focal length lens (as opposed to the 85mm of the earlier captures). This is a good sharp lens. The image consist of a mean stack of three 60 second frames taken with a 7nm H-alpha filter and then three 1 second frames taken with a luminance filter added to the stack using sum stacking. This technique makes use of the new capability of the current version of StarlightLive to switch between different stacking modes. The H-alpha exposures are assigned to the red channel and the luminance frames are assigned to all channels. Without switching between the stacking modes this would not be possible.

My goal was to show M24 in its full physical complexity. This is a very interesting and unique object. The star cloud is essentially an enormous open cluster of young O and B type stars that are still embedded in the cloud of Hydrogen gas that they were born of. They ionize the gas that then glows red. I wanted to display both the red glow of the ionized Hydrogen and the white light of the stars in the same image. Aesthetically the plain black and white simple H-alpha capture of Post #2 may look more elegant and pleasing. But in my opinion, the three color red, white and black image better conveys the physical structure of the object. That we see its two different physical layers, we see it in two stages of its cosmic evolution, gaseous and stellar,  that are still simultaneously present.

Anyway, this is it for M24 for now. We should revisit it next year, when it is higher in the sky and there are no clouds interfering.

Clear Skies!  --Dom

Edited by Dom543
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Beautiful capture(s) of this fascinating region, one of my favourite binocular objects. I like the subdued yet informative colour theme.

I've always found the rectangular shape quite strange in the natural world (although in your shot, what with the dark lanes, I see a dog's head looking left, complete with eye and ear).

Martin

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Milky Way Petroglyphs

LDN772 in Vulpecula

LDN772.Milky.Way.Petroglyphs_2016.9.27_00.05.14_65%.jpg

 

B138 in Aquila

B138.Black.Lizard_2016.9.26_23.35.39_vert_65%.jpg

Single 5 second exposures with Samyang 135mm lens at f/2.0 and Ultrastar Sr.

Both open for interpretation.

Clear Skies!  --Dom

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