APOD: NGC 891 vs Abell 347 (2016 Nov 12)

[APOD Robot]

NGC 891 vs Abell 347

Explanation: Galaxies abound in this well-chosen field of view that spans about 1 degree on the sky toward the northern constellation Andromeda. At top right is large spiral galaxy NGC 891, 100 thousand light-years across and seen almost exactly edge-on. About 30 million light-years distant, NGC 891 looks a lot like our own Milky Way with a flattened, thin, galactic disk. Its disk and central bulge are cut along the middle by dark, obscuring dust clouds. Scattered toward the lower left, and beyond a foreground of Milky Way stars, are members of galaxy cluster Abell 347. Nearly 240 million light-years away, Abell 347 shows off its own large galaxies in the sharp telescopic image. They are similar to NGC 891 in physical size but located almost 8 times farther away, so Abell 347 galaxies have roughly one eighth the apparent size of NGC 891.

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[Boomer12k]

Such a good comparison shot...

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[Ann]

I should have replied to this image yesterday, but better late than never. Thanks, Juan Lozano de Haro, what an interesting picture! I wasn't aware that there is a galaxy cluster located apparently right next to NGC 891, although in reality NGC 891 and Abell 347 are of course separated by vast distances in space.

To the lower right of the bright yellow star is an edge-on galaxy, NGC 898, that looks very much like NGC 891, except that it hasn't got a visible dust lane. I guess the apparent size of NGC 898 is really just one eighth of the apparent size of NGC 891, and NGC 898 may well be eight times farther away. Interesting!

Click to view full size image

NGC 891. Photo: Bob Franke.

You will forgive me now for talking about NGC 891, because it is really such an interesting galaxy. It is definitely one of the most perfectly edge-on galaxies I know. The bright nucleus is completely hidden by the central dust lane, and it is almost impossible to say which half of the bulge, the upper half or the lower half, sticks out more from the dust lane.

Note, too that NGC 891 has a very extensive yellow disk. At least half of its disk appears to be yellowish, and only the relatively faint outer half of it is bluish, apparently from intermediate-aged stars of spectral classes A and F.

Click to view full size image

NGC 4565. Photo: Johannes Schedler.

It is interesting to compare NGC 891 with similarly edge-on (but not as perfectly edge-on) NGC 4565. Note that NGC 4565 has a more extended disk than NGC 891 and is larger in overall size. Note that it has a larger component of A- and F-type stars in its disk, since its disk is bluer than the disk of NGC 891. But note, too, that its dust lane is a lot more "quiet" than the dust lane of NGC 981.

The dust lane of NGC 891 is a busy place. Note the obvious blue star clusters on the left side of the central dust lane in Bob Franke's picture. As for NGC 4565, it is not certain that the overall mottling of the dust lane represents anything else than different levels of extinction by dust.

Also note the large number of smoking "chimneys" in the dust lane of NGC 891. Many supernovas have popped off here. The dust lane of NGC 4565 is much less disturbed and displays a much smaller number of obvious chimneys.

In a way, NGC 891 is like a small fast car outrunning its slow, steady competitor.

Ann

[EArHog]

About how many Milky Way stars are included in that APOD? I assume that all but a few of the "objects" in the pic are distant galaxies, and maybe 6 to 10 local stars ?

[geckzilla]

About how many Milky Way stars are included in that APOD? I assume that all but a few of the "objects" in the pic are distant galaxies, and maybe 6 to 10 local stars ?

It's not especially far from the galactic plane, but it's also not looking toward the core. There are a good number of Milky Way stars in the image. I'd say many more than a dozen, probably several hundred at least.

[Visual_Astronomer]

About how many Milky Way stars are included in that APOD? I assume that all but a few of the "objects" in the pic are distant galaxies, and maybe 6 to 10 local stars ?

It's not especially far from the galactic plane, but it's also not looking toward the core. There are a good number of Milky Way stars in the image. I'd say many more than a dozen, probably several hundred at least.

Oh, I think there are many, many Milky Way stars shown here. (many hundreds) I would not assume that most of these points are galaxies.