APOD: Hidden Galaxy IC 342 (2017 Jul 08)

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APOD: Hidden Galaxy IC 342 (2017 Jul 08)

Postby APOD Robot » Sat Jul 08, 2017 4:06 am

Image Hidden Galaxy IC 342

Explanation: Similar in size to large, bright spiral galaxies in our neighborhood, IC 342 is a mere 10 million light-years distant in the long-necked, northern constellation Camelopardalis. A sprawling island universe, IC 342 would otherwise be a prominent galaxy in our night sky, but it is hidden from clear view and only glimpsed through the veil of stars, gas and dust clouds along the plane of our own Milky Way galaxy. Even though IC 342's light is dimmed by intervening cosmic clouds, this sharp telescopic image traces the galaxy's own obscuring dust, blue star clusters, and glowing pink star forming regions along spiral arms that wind far from the galaxy's core. IC 342 may have undergone a recent burst of star formation activity and is close enough to have gravitationally influenced the evolution of the local group of galaxies and the Milky Way.

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Re: APOD: Hidden Galaxy IC 342 (2017 Jul 08)

Postby Ann » Sat Jul 08, 2017 10:37 am

Today's APOD appears to be a repeat from January 9, 2008.

In some ways I find the image very beautiful indeed. What I like best is that the galaxy appears to be suffused with an inner, pearly light that almost seems to jump off the page. When the picture is seen against a dark background, you can almost imagine that the picture you're looking at is the real thing seen through a telescope. And then you can marvel at all the details you can see and the amazing, mildly yellow-white glow of the galaxy, seen against all the blackness. (But no... there is no way you could see so many details and so much color through a telescope.)

IC 342. Photo: Stephen Leshin.














Okay. And this is what I don't like much about today's APOD.

Compare T. Rector's image with Stephen Leshin's. Leshin's image lacks the "inner glow" of Rector's picture. But please note all the blue foreground stars in Leshin's image. There are no blue foreground stars at all in Travis Rector's picture. Most foreground stars there are yellow-orange, and a few are whitish.

The long and the short of it is that I don't like Travis Rector's treatment of blue objects in the universe, or his treatment of the color blue in itself. Often, he doesn't obey the "convention" when it comes astrophtography, which is that the exposure taken through the shortest-wavelength filter should be colored blue, the exposure through the longest wavelength filter should be colored red, and the exposure thought the intermediate filter should be colored green.

NGC 3310.
Photo: NASA and The Hubble Heritage Team (STScI/AURA)
NGC 3310. Photo: Adam Block.




















Take a look at these two images of NGC 3310. They look very different, because they have been taken through different filters and mapped differently, but they both obey the rule that the hottest parts of the galaxy should look blue, the intermediate parts should be green, and the coolest one should be red. (Adam Block has also used an Ha filter to bring out pink emission nebulas.)

We can see, in both images, that the hottest, bluest part of NGC 3310 is the inner spiral and inner ring. The Hubble image shows us that the small inner bulge contains the coolest, reddest stars of the galaxy. (In Adam Block's image, this part of the galaxy is overexposed, although it does appear to have a faintly reddish tinge.) And we can see, in both images, that the outer, diffuse parts of the galaxy are less blue than the inner spiral. In the Hubble image these parts look almost green, but in Adam Block's picture they are still blue.

NGC 3310. AAO ITSO Office, Gemini Obs./AURA & T. A. Rector (U. Alaska Anchorage).
Now take a look at Travis Rector's picture of NGC 3310. It is indeed beautifully detailed, but notice the colors. The inner spiral is all red, and the inner ring, as well as the inner bulge, is white. The only blue parts of the galaxy are the outer, diffuse parts.

Why does the galaxy look like that? Well, this page tells us that the filters used for this galaxy are a blue (B) filter, coded blue, one red (R) and green filter, coded red (or green? or both red and green?), and one Ha filter, coded red. This means that the only parts of the galaxy that have any chance of looking blue in this picture are the parts that are neither generally red, generally green nor specifically hydrogen alpha-red. The only parts of the galaxy that fit that bill are the outermost ones, which are far less blue than the inner spiral.

I find Travis Rector's use of color confusing, and as a Color Commentator I can't entirely approve of him.

Ann
Last edited by Ann on Sat Jul 08, 2017 1:43 pm, edited 1 time in total.
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Re: APOD: Hidden Galaxy IC 342 (2017 Jul 08)

Postby bystander » Sat Jul 08, 2017 12:13 pm

ESA Hubble recently posted an image of the heart of IC 342 and an APOD search for "Hidden Galaxy IC 342" brings up five different images of IC 342.
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Jim Armstrong

Re: APOD: Hidden Galaxy IC 342 (2017 Jul 08)

Postby Jim Armstrong » Sat Jul 08, 2017 3:38 pm

Ann's well thought out post is hard to follow.
I don't like the term "island universe." The term "universe" already has a quite different meaning: all.
I think "island in the universe" is clearer term for a galaxy.

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Re: APOD: Hidden Galaxy IC 342 (2017 Jul 08)

Postby bystander » Sat Jul 08, 2017 6:12 pm

"Island Universe" is a historic term coined by 18th century philosopher Immanual Kant who believed the "spiral nebulae" were extra-galactic back in a time when it was still believed that the Milky Way was the universe. It is still used to poetically describe galaxies to this date.
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

heehaw

Re: APOD: Hidden Galaxy IC 342 (2017 Jul 08)

Postby heehaw » Sat Jul 08, 2017 9:07 pm

Ah, but think about the civilizations present in THAT galaxy, past present & future! They see OUR galaxy EDGE ON! They LOVE their own photos of OUR galaxy!

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Re: APOD: Hidden Galaxy IC 342 (2017 Jul 08)

Postby Chris Peterson » Sat Jul 08, 2017 9:58 pm

Jim Armstrong wrote:Ann's well thought out post is hard to follow.
I don't like the term "island universe." The term "universe" already has a quite different meaning: all.
I think "island in the universe" is clearer term for a galaxy.

To use your form, I'd say "Island in the Universe". Because as long as "universe" is expressed as a common noun, it has many meanings besides the one (and presumably only) universe that we are part of. Viewed that way, "island universe" works, both technically and poetically.
Chris

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Re: APOD: Hidden Galaxy IC 342 (2017 Jul 08)

Postby De58te » Sat Jul 08, 2017 10:19 pm

But think of a civilization in that galaxy looking at the Andromeda Galaxy. Andromeda is close to Camelopardalis in the sector of space, just not in line but across from the rim of the Milky Way. M31 is about 2 million light years away, so it would be about 8 million light years from IC 342, not considering the angle offset. If Andromeda is even bigger than the Milky Way, and it would be more face on to IC 342, then that civilization is probably marveling at Andromeda instead of the Milky Way.

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Re: APOD: Hidden Galaxy IC 342 (2017 Jul 08)

Postby ThePiper » Sat Jul 08, 2017 11:12 pm

Curious: All these pinky starworms... :shock:

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Re: APOD: Hidden Galaxy IC 342 (2017 Jul 08)

Postby Ann » Sun Jul 09, 2017 6:31 am

ThePiper wrote:Curious: All these pinky starworms... :shock:


The Milky Way with pink emission nebulas.
Photo: ESO(?)
Those pink star worms are emission nebulas.

We have them in the Milky Way, too. In the picture at left, you can spot some pink splotches in the thick dust lane of the Milky Way. You can also see some pink clouds above the dust lane of the Milky Way. The most prominent of these clouds is the very big round thing at 11 o'clock. You can see that there is a white star inside the big red cloud. That star is Zeta Ophiuchi, a very hot (32,500 Kelvin) star that has been kicked out of its birthplace and is now zipping along in space. Zeta Oph has run into a gas cloud, and because Zeta is so hot, it injects a lot of energy into the gas around it and makes it shine red.

Zeta Ophiuchi is quite nearby, some 400 light-years away. The pink splotches in the dust lane of the Milky Way are much farther away, some 5,000 light-years or more, which is why they look smaller than the Zeta Ophiuchi cloud. In reality, they are bigger. The brightest of these pink splotches (on the left side of the picture) are big gas clouds where many hot stars have been born at more or less the same time. The stars in these bright pink splotches have not been kicked out of their birth place, but are still inside it. The pink clouds surrounding one or many very hot and very young stars are called emission nebulas.

There are very many emission nebulas in IC 342. They do line up to form what looks like pink worms.

Ann
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Re: APOD: Hidden Galaxy IC 342 (2017 Jul 08)

Postby ThePiper » Sun Jul 09, 2017 7:02 pm

Ann wrote:
ThePiper wrote:Curious: All these pinky starworms... :shock:

...
Zeta Ophiuchi is quite nearby, some 400 light-years away. The pink splotches in the dust lane of the Milky Way are much farther away, some 5,000 light-years or more, which is why they look smaller than the Zeta Ophiuchi cloud. In reality, they are bigger. The brightest of these pink splotches (on the left side of the picture) are big gas clouds where many hot stars have been born at more or less the same time. The stars in these bright pink splotches have not been kicked out of their birth place, but are still inside it. The pink clouds surrounding one or many very hot and very young stars are called emission nebulas.

There are very many emission nebulas in IC 342. They do line up to form what looks like pink worms.
Ann


Thank you Ann, you are an excellent teacher, always with stunning news! I didn't know the story behind Zeta Ophiuchi, now lurking over our heads and - soon - swinging back to the plane like a pendulum. Time to buy a helmet! :ohno:

sillyworm2

Re: APOD: Hidden Galaxy IC 342 (2017 Jul 08)

Postby sillyworm2 » Tue Jul 25, 2017 6:52 pm

Chris Peterson wrote:
Jim Armstrong wrote:Ann's well thought out post is hard to follow.
I don't like the term "island universe." The term "universe" already has a quite different meaning: all.
I think "island in the universe" is clearer term for a galaxy.

To use your form, I'd say "Island in the Universe". Because as long as "universe" is expressed as a common noun, it has many meanings besides the one (and presumably only) universe that we are part of. Viewed that way, "island universe" works, both technically and poetically.

Shouldn't it be "Island in A Universe"?

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Re: APOD: Hidden Galaxy IC 342 (2017 Jul 08)

Postby Chris Peterson » Tue Jul 25, 2017 7:33 pm

sillyworm2 wrote:
Chris Peterson wrote:
Jim Armstrong wrote:Ann's well thought out post is hard to follow.
I don't like the term "island universe." The term "universe" already has a quite different meaning: all.
I think "island in the universe" is clearer term for a galaxy.

To use your form, I'd say "Island in the Universe". Because as long as "universe" is expressed as a common noun, it has many meanings besides the one (and presumably only) universe that we are part of. Viewed that way, "island universe" works, both technically and poetically.

Shouldn't it be "Island in A Universe"?

There is "the Universe" and "a universe". In this case, it's an island universe. You could say it's "an island in a universe", or "an island in the Universe", but either way you lose the historical context of the term.
Chris

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