Star Cluster M7 Rich Milky Way Field in Scorpius

Uploaded 7/10/10

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Minkowski 1-30
Sanduleak 2-253
Above: Close ups of parts of the main image

M7 is located just off the stinger stars of the far southern constellation of Scorpius, now riding high due south on July evenings. A favorite object of mine is this cluster because it is buried inside a very rich star cloud in the Milkyway, and features several dark nebula, a globular cluster, and several faint planetary nebula in the one 2.5 degree field seen above, with north up.

Just to the left of center is the splashy open cluster M7. Spanning over 80 arc minutes in size, this 3.3 magnitude object is one of the most brilliant of its type in the entire sky. About 80 cluster members dominate this object, most being blue B super giants with a few orange K types.

Near the right edge of this field you will find the diminutive faint globular cluster NGC6453 highlighted in the center small panel above. This 10.2 magnitude object is 8 arc minutes in size and has a distinctly yellow color due to the amount of dust in this part of the Milkyway.

Even more interesting are the two tiny planetary nebula in this field. The first, highlighted in the left sub panel is M1-30, appearing as an intense orange star to the upper right of the cluster. It is 14.7 magnitude, and very tiny at 5 arc seconds in size. Apparently this object has a lower level of ionizing excitation than Sanduleak 2-253, which is to the lower right of M7 appearing as a diffuse teal (blue-green) fuzzy star. The blues to create this color are from Hbeta and OIII lines. It appears as a sizable disk, spanning 9 arc seconds in width as seen on the right sub panel.

Processing Notes:

This object is in a part of the Milkyway that is so obscured with dust, everything appears a shade of brown or yellow. To remove the brown hue and show the field as it would be without dust obscuration seen here, you have to histogram equalize all three color channels in Photoshop over the entire image. To do this you can either stretch all three colors histograms so they start and stop at the same point. Or using adjustment layers you can do a really neat trick to equalize the histograms which is what I did here. To do this, you duplicate the image in a layer over the main image. Next add an adjustment layer for Levels over the new layer. you then blur most of or part of the duplicate image with a Gaussian blur so huge the entire image is one solid color - brownish. In the levels adjustment layer, click the gray eyedropper on the blurred image to make it spectrally flat - gray. Then delete the duplicated blurred layer. The adjustment layer stays on top of the original image and fully histogram equalizes it. Flatten and your done.

Optics: 8" f/4 Newtonian Astrograph w/Baader MPCC Coma Corrector Platform: Astrophysics AP1200 Camera: Hutech Modified Canon XTi @ ISO800 Exposure: 3 x 5m = 15 minutes Location: Payson, Arizona Elevation: 5150 ft. Sky: Seeing 4/10, Transparency 7/10 Outside Temperature: 65F Processing Tools: Photoshop CS2, Images Plus 3.82 HOME GALAXIES EMISSION NEBS REFLECTION NEBS COMETS GLOBULARS OPEN CLUST PLANETARIES LINKS