Centered on the invisible black hole called Sagittarius A*, infrared light from the Spitzer and WISE missions provides us a
glimpse into what otherwise appears visually as a dark band in the constellation of Sagittarius. As you can see, it's a busy place bustling with star formation evidenced by glowing nebulas.
Because there is no separation between nearer and more distant structures, it's quite confusing. Imagine taking an x-ray of your body looking down from the top of your head with all your bones together on a single, flat plane. We can guess that larger structures are generally closer to us and the smaller ones are generally farther in the distance, but it's not always true, so it's best to take any interpretations about spatial positioning with a grain of salt. We know with our skeletal x-ray that our teeth are attached to our skull, but we don't have that advantage with our infrared view of the galaxy.
Still, it is tempting to make some general observations. Notice that there seems to be a lot of grayish-colored dust and gas sweeping outward from the center to the right side of the frame. Are we looking at the central part of an arm of our galaxy sweeping outward and toward us? Is the left side of the image the opposing arm receding in the other direction? Maybe. It does seem like some maps illustrating the Milky Way match up with this guess.
Some notes on the processing:
Once again I have made use of two Spitzer bands MIPS1/24μm and IRAC4/8μm for the red and blue channels, respectively. WISE's W3/12μm takes the green channel. Because the W3 and the MIPS1 data are so much less crisp than the IRAC4 data, I've used the IRAC4 data as a luminance layer in Photoshop. There's a bit of complexity in how I applied it. The green channel was also more strongly affected than the red channel.
One of the challenges of combining Spitzer and WISE data is that WISE imagery is at a much lower resolution. This causes some unsightly green glows around many of the stars. To deal with it this time I used a combination of a "Minimum" filter applied to the greenest areas. What this does is kind of shrink the spread of the star so it's more contained. Later on I also applied a channel mixer on some remaining green halos to nearly eliminate the glow. I think it worked really well without compromising the image quality in other ways too much.
Nov. 25 2016: I updated this image. Improvements should only be visible at around 100% zoom on the full size image. Overall image from lower zoom levels wasn't affected much.
Red: Spitzer/MIPS1 (24μm)
Green: WISE/W3 (12μm)
Blue: Spitzer/IRAC4 (8μm)
North is NOT up. It is around 60° counter-clockwise from up.
