APOD: NGC 247 and Friends (2020 Jan 16)

[APOD Robot]

NGC 247 and Friends

Explanation: About 70,000 light-years across, NGC 247 is a spiral galaxy smaller than our Milky Way. Measured to be only 11 million light-years distant it is nearby though. Tilted nearly edge-on as seen from our perspective, it dominates this telescopic field of view toward the southern constellation Cetus. The pronounced void on one side of the galaxy's disk recalls for some its popular name, the Needle's Eye galaxy. Many background galaxies are visible in this sharp galaxy portrait, including the remarkable string of four galaxies just below and left of NGC 247 known as Burbidge's Chain. Burbidge's Chain galaxies are about 300 million light-years distant. NGC 247 itself is part of the Sculptor Group of galaxies along with the shiny spiral NGC 253.

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[Ann]

I find today's APOD a delightful picture with absolutely lovely colors and great details!

Look at Burbidge's Chain at left. Note that you can see little pink Hα emission nebulas inside them! Note the green splotch in one of the galaxies, which I can't explain. And note that the two galaxies farthest to the lower left are very clearly interacting and exchanging matter!

You may note, too, a lot of small orange spots in the background. Many of them definitely have disks, which are more visible in the full size version of the APOD itself. So most of them are background galaxies, while one or a few others might be either faint foreground stars or bright red giant in the halo of NGC 247.

The picture showing parts of the disk of NGC 247 demonstrates the difficulty in spotting the difference between background galaxies and red supergiant stars in NGC 247 itself. We know that a stellar population of the kind we see in parts of NGC 247 is going to contain red giants, and a picture like today's APOD should definitely resolve some of them. But it is also clear that there are background galaxies in the picture, some of which are going to be very reddened by redshift reddening. So which of the orange points are stars and which are galaxies?

Jame D Wray said in his book The Color Atlas of Galaxies that supergiant stars of all colors appear about equally bright in UBV images. Well, today's APOD is certainly not a UBV image, but I'm going to take my cue from James D Wray anyway and say that the orange points that appear much brighter than any individual blue stars in NGC 247 are probably not supergiant members of NGC 247, but instead background galaxies. If you look at the full size image of the APOD itself, you can more easily discern the fainter orange spots in the disk of NGC 247 that may be more likely to be red giant stars in NGC 247.

Ann

[orin stepanek]

NGC247hager_1024.jpg (48.65 KiB) Viewed 2301 times

Neighborhood Galaxy; really a neat Galaxy! Howdy neighbor; Oh; I guess they can't hear me!

[sillyworm 2]

GALAXIES..my favorite apods.I could look at and read about all day long.

[zelaza]

With the concern about interference from vast arrays of communications satellites (Starling, etc.), could someone show what this galaxy picture would look like if satellites intruded over the exposure time of this scene.

[Chris Peterson]

With the concern about interference from vast arrays of communications satellites (Starling, etc.), could someone show what this galaxy picture would look like if satellites intruded over the exposure time of this scene.

While there could well be satellites passing through the field during the exposure, they would have no impact on the final image, as such images are always made from stacks of shorter exposures, and anomalous pixels are automatically eliminated. It's not unusual even now for individual images in a stack to have satellites, airplanes, or meteors in them. These do not make it to the processed image.