by Ann » Fri Aug 13, 2021 6:09 am
There is a greenish cast to much of the face of M74 that rubs me the wrong way... sorry...
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
[float=left][attachment=1]M74 APOD color annotated.png[/attachment][/float][float=right][attachment=0]Star formation in M74 APOD.png[/attachment][/float]
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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!
[float=left][img3="Grand design galaxy M81. Image: NASA, ESA and the Hubble Heritage Team (STScI/AURA)."]https://www.nasa.gov/sites/default/files/styles/full_width/public/thumbnails/image/m81-print.jpg?itok=cQ8vTd7C[/img3][/float][float=right][img3="A part of the Andromeda Galaxy. Image: NASA, ESA, J. Dalcanton, B.F. Williams, and L.C. Johnson (University of Washington), the PHAT team, and R. Gendler"]https://www.nasa.gov/sites/default/files/styles/full_width/public/thumbnails/image/hs-2015-02-a-hires_jpg.jpg?itok=-DDRNP3D[/img3][/float]
[clear][/clear]
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 [url=https://astrobackyard.com/ngc-4565-needle-galaxy/]edge on spirals[/url].
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...
[float=left][img3="Grand design galaxy NGC 1566. Credit: ESA/Hubble & NASA. Acknowledgement: Det58"]https://upload.wikimedia.org/wikipedia/commons/thumb/6/62/Potw1422a.jpg/1024px-Potw1422a.jpg[/img3][/float]
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How big is [url=https://en.wikipedia.org/wiki/NGC_1566]NGC 1566?[/url]
Ann