APOD: A Perfect Spiral (2021 Aug 13)

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APOD: A Perfect Spiral (2021 Aug 13)

Post by APOD Robot » Fri Aug 13, 2021 4:06 am

Image A Perfect Spiral

Explanation: If not perfect then this spiral galaxy is at least one of the most photogenic. An island universe of about 100 billion stars, 32 million light-years away toward the constellation Pisces, M74 presents a gorgeous face-on view. Classified as an Sc galaxy, the grand design of M74's graceful spiral arms are traced by bright blue star clusters and dark cosmic dust lanes. This sharp composite was constructed from image data recorded by the Hubble Space Telescope's Advanced Camera for Surveys. Spanning about 30,000 light-years across the face of M74, it includes exposures recording emission from hydrogen atoms, highlighting the reddish glow of the galaxy's large star-forming regions. With a lower surface brightness than most galaxies in the Messier catalog, M74 is sometimes known as the Phantom Galaxy.

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Ann
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Re: APOD: A Perfect Spiral (2021 Aug 13)

Post by Ann » Fri Aug 13, 2021 6:09 am

M74 APOD color annotated.png
Star formation in M74 APOD.png

There is a greenish cast to much of the face of M74 that rubs me the wrong way... sorry... :cry:

Is it a good picture, though? Oh sure, there is a ton of details in the image. Just look at the fantastic site of star formation in the lower left corner, where a truly majestic enormous cluster has burst forth from the tattered remnants of a huge red nebula. It's awesome!


Just for the fun of it, let's compare today's picture of M74, which is based on data from Hubble, with Hubble images of M81 and the Andromeda Galaxy. It is interesting to see how extremely bulge-dominated M81 is, and how faint and relatively thin its spiral arms are, compared with the general morphology of M74. Today's APOD is a reminder that even in M74, the nucleus and bulge dominate the galaxy's light output. But the arms of M74 are long and brilliantly studded with bright blue stars and red emission nebulas.

The reason why M74 is called the Ghost galaxy is, of course, that its bulge is fainter than the bulges of most galaxies, and its arms, while bright as galactic spiral arms go, are considerably fainter than the bulge. And because we see the arms face on, their light isn't "added up" the way they are in edge on spirals.

We may note, too, that M74 is a comparatively small and delicate spiral. My impression is that a smallish size is fairly typical of elegant spirals, even if this is not always the case. That makes me wonder...


How big is NGC 1566?

Ann
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orin stepanek
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Re: APOD: A Perfect Spiral (2021 Aug 13)

Post by orin stepanek » Fri Aug 13, 2021 12:56 pm

m74_APOD1024.jpg
Beautiful Spiral! Of coarse most galaxies are! Our galaxy was
thought of the universe; now called an island universe! Oh so
wondrous is is the mysterys of space!😉
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Re: APOD: A Perfect Spiral (2021 Aug 13)

Post by neufer » Fri Aug 13, 2021 3:30 pm

Click to play embedded YouTube video.
Art Neuendorffer

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Re: APOD: A Perfect Spiral (2021 Aug 13)

Post by SeedsofEarth » Fri Aug 13, 2021 6:14 pm

In the bottom edge center of the picture, there is a cluster of objects that appears too regular to be normal. There are four red objects neatly aligned, and just above them are three lighter objects also neatly aligned and fitted between the four objects below them. Is this a photographic aberration, or just a coincidental astrological arrangement?

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johnnydeep
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Re: APOD: A Perfect Spiral (2021 Aug 13)

Post by johnnydeep » Fri Aug 13, 2021 8:35 pm

SeedsofEarth wrote:
Fri Aug 13, 2021 6:14 pm
In the bottom edge center of the picture, there is a cluster of objects that appears too regular to be normal. There are four red objects neatly aligned, and just above them are three lighter objects also neatly aligned and fitted between the four objects below them. Is this a photographic aberration, or just a coincidental astrological arrangement?
I presume you mean these things:

M74 Artifact or Objects.JPG

Yes, that looks too artificial to be entirely real, but I'll hold judgement until others weight in.
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Chris Peterson
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Re: APOD: A Perfect Spiral (2021 Aug 13)

Post by Chris Peterson » Fri Aug 13, 2021 8:44 pm

johnnydeep wrote:
Fri Aug 13, 2021 8:35 pm
SeedsofEarth wrote:
Fri Aug 13, 2021 6:14 pm
In the bottom edge center of the picture, there is a cluster of objects that appears too regular to be normal. There are four red objects neatly aligned, and just above them are three lighter objects also neatly aligned and fitted between the four objects below them. Is this a photographic aberration, or just a coincidental astrological arrangement?
I presume you mean these things:


M74 Artifact or Objects.JPG


Yes, that looks too artificial to be entirely real, but I'll hold judgement until others weight in.
You can compare today's image with the one at Hubblesite and see that this is a processing artifact of some kind. There's also an odd geometric distortion in today's image.
Chris

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