The Winter Milkyway

from Payson

Uploaded 1/13/07

Our moderately light polluted skies yielded this image, from a 70 minute averaged stack of images. This closely matches what the eye would see.

The same image after processing with gradient contrast masks in Photoshop.


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 The test phase of the Hutech XTi is over, and some real astro imaging can begin! We start with this set of images, taken this week from our mag 4 - 6 skies (depending on direction) here in Payson. I was very curious as to whether the Halpha Pass Filter would perform with todays glow from high pressure sodium lamps. Careful processing of the 70 minutes of RGB data yielded a fine constellation shot, with some red but little blue nebulosity. (Because the sky fog subtracted it) When combined with 60 minutes of the red data from the filter, the results were more representative of a dark sky shot.

Image Description:

This image encompasses the most spectacular portion of the Winter Milkyway. On the bottom is the constellation of Orion, brimming with red hydrogen nebulosity. The large "C" shaped arc is Barnards Loop, and above it a huge red circular nebula known as the "Lambda Orionis Nebula". Inside Barnards Loop is the three belt stars and the "Zeta Orionis" nebulosity complex, which contains the Horsehead Nebula. Of VERY special note is the red strip of nebulosity on the far right edge of the image, going up and down. This nebula, in Eridanus I had never photographed until now. It is the right side of Barnards Loop that has been blown off by the fierce stellar winds of the belt stars region.

To the left of Orion along the edge is the bright small nebula the "Rosette Nebula". Just above it is the "S Monoceros" nebulosity complex, which includes "Hubbles Variable Nebula"

Two regions of nebulosity are along the upper half of the image. On the upper right of the frame is the huge "California Nebula" in Perseus. Just below it is the brilliant star cluster the " Seven Sisters" or "Pleiades". On the upper left is a region of red nebulous patches inside the constellation of Auriga. This includes IC405 and hordes of star clusters.

A snaking and branching chain of dark nebula flow down from the top center of the frame, and engulf the Lambda Orionis nebula. Most of these have Barnard number designations.

Image Processing:

Once such a strong light pollution gradient is removed from an image, the star magnitude limits across the frame varies considerably. In regions of high light pollution, there are few stars. To correct for this, I used gradient contrast masks in Photoshop. You create an adjustment layer in Photoshop for Levels. Then using the gradient tool, create a gradient from black to white on the adjustment layer mask, so that the white is over the areas of diminished stars and the black over the darker skies areas. You then increase the contrast of the frame by bringing in the top and bottom sliders in the Levels control. This when combined with the mask brings up the stars and contrast more in the diminished areas, and evens out the entire image to appear like a shot from a dark sky site.

The red light shot, with the Lumicon filter was added to the RGB image by splitting the image into separate channels, and combining the red light data onto the R channel with Screen at 100%, and to the B channel at 10%. Backgrounds were readjusted to original values and the three channels were then recombined for the final image.

 One hour of red light data taken with a Lumicon Halpha Pass filter, which is a very high quality equivalent to the old Wratten 92 filters. An 80mm sized interference filter over the objective would be cost prohibitive and the wide range of angles of incidence would render the filter ineffective over such a wide field. This is the R channels only.

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Instrument: Canon 17 - 40mm L at 17mm f/4.5 Platform: Astrophysics 1200 QMD/Piggyback on 12.5" Camera: Hutech Modified Canon XTi @ ISO800 Exposure: 130m (13 x 10m) Filters: Lumicon Halpha Pass Location: Payson, Arizona Elevation: 5150 ft. Sky: Seeing 5/10, Transparency 7/10 Outside Temperature: 30F Processing Tools: Photoshop CS2, Maxim DL, Canon RAW HOME GALAXIES EMISSION NEBS REFLECTION NEBS COMETS GLOBULARS OPEN CLUST PLANETARIES LINKS FastCounter by bCentral