APOD: IC 342: The Hidden Galaxy (2019 Jan 16)

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APOD: IC 342: The Hidden Galaxy (2019 Jan 16)

Post by APOD Robot » Wed Jan 16, 2019 5:13 am

Image IC 342: The Hidden Galaxy

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 and reddened by intervening cosmic clouds, this sharp telescopic image traces the galaxy's own obscuring dust, young 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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Ann
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Re: APOD: IC 342: The Hidden Galaxy (2019 Jan 16)

Post by Ann » Wed Jan 16, 2019 11:50 am

Today's APOD is a nice and interesting picture, and IC 342 is an interesting and photogenic galaxy. Not that it would look as colorful as it does in this picture this without a hefty dose of saturation, given the fact that most of its color (as seen by us) will be "killed" by dust extinction, and the red hue of hydrogen alpha (which may penetrate the dust) is practically always invisible to humans when it is being sent our way by emission nebulas.

The Hα filter was obviously made to work hard in producing this APOD, in order to produce all those ruby-red nebulas adorning the arms of IC 342 here. (But don't get me wrong, I'm not complaining!)

M74. Photo: Isaac Newton Group of Telescopes.
IC 342. Photo: Arturas Medvedevas























In any case, IC 342 is a pleasantly symmetrical galaxy, slightly reminiscent of Messier 74. As you can see, IC 342 is a bit more irregular than M74. That suggests that IC 342 is more affected by star formation than M74. Either there is actually more star formation going on in IC 342 than in M74, or, alternatively, IC 342 is a less massive galaxy than M74 so that it more easily gets distorted by the extremely strong winds of massive star formation.

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Re: APOD: IC 342: The Hidden Galaxy (2019 Jan 16)

Post by NCTom » Wed Jan 16, 2019 12:42 pm

Where is our solar system in relation to IC342? Are we looking through nearside galactic clouds or across a much greater chunk of our galaxy? Not that I'll be around to see it, but if we are on the far side of the galaxy from IC342, in about 115 million years we should have a great picture of this beautiful group of stars!

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Re: APOD: IC 342: The Hidden Galaxy (2019 Jan 16)

Post by MarkBour » Wed Jan 16, 2019 6:08 pm

Ann wrote:
Wed Jan 16, 2019 11:50 am
As you can see, IC 342 is a bit more irregular than M74. That suggests that IC 342 is more affected by star formation than M74. Either there is actually more star formation going on in IC 342 than in M74, or, alternatively, IC 342 is a less massive galaxy than M74 so that it more easily gets distorted by the extremely strong winds of massive star formation.

Ann
That's an interesting take on this. All I have heard so far goes the other direction: Gravitational "events" cause distortions, and then disruption of gas clouds, which then brings on bursts of star formation. I did not think that star formation could cause spiral arm distortions on the galactic scale. (Meaning that they could deform a spiral arm enough that it would be noticeable to an observer looking at an image of a galaxy at this scale.)
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Re: APOD: IC 342: The Hidden Galaxy (2019 Jan 16)

Post by E Fish » Wed Jan 16, 2019 6:12 pm

Is there a picture of what we can actually see if we just look at it through a regular telescope? For obvious reasons, all the pictures I've been able to find are after long exposures. I'm just curious about what we actually see ourselves. Is it fully obscured by the dust and gas of the plane of the galaxy or can we see the shape but there are lots of stars in the way?

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Re: APOD: IC 342: The Hidden Galaxy (2019 Jan 16)

Post by Chris Peterson » Wed Jan 16, 2019 6:56 pm

E Fish wrote:
Wed Jan 16, 2019 6:12 pm
Is there a picture of what we can actually see if we just look at it through a regular telescope? For obvious reasons, all the pictures I've been able to find are after long exposures. I'm just curious about what we actually see ourselves. Is it fully obscured by the dust and gas of the plane of the galaxy or can we see the shape but there are lots of stars in the way?
This galaxy is bright but large, so its surface brightness isn't very great. It's not hard to see visually with a smallish (6-8") scope under dark skies. The core, at around mag 12, is obvious, but the much larger disc around it decreases rapidly in brightness. Like all galaxies, it just looks like a fuzzy gray blob. At low magnification (as with binoculars) it's easy to see, but it looks almost stellar. It's a standard target for visual astronomers.
Chris

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Re: APOD: IC 342: The Hidden Galaxy (2019 Jan 16)

Post by BDanielMayfield » Wed Jan 16, 2019 8:50 pm

NCTom wrote:
Wed Jan 16, 2019 12:42 pm
Where is our solar system in relation to IC342? Are we looking through nearside galactic clouds or across a much greater chunk of our galaxy? Not that I'll be around to see it, but if we are on the far side of the galaxy from IC342, in about 115 million years we should have a great picture of this beautiful group of stars!
Our solar system is between IC 342 and the Milky Way's core (roughly), so we're looking at it in a favorable time in the sun's orbit about the MWs center. Perhaps as the sun bobs up and down in the disk along it's orbit we might get some better viewing periods, but in general we're seeing it about as good as it will get. :(

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Re: APOD: IC 342: The Hidden Galaxy (2019 Jan 16)

Post by Ann » Thu Jan 17, 2019 1:13 am

MarkBour wrote:
Wed Jan 16, 2019 6:08 pm
Ann wrote:
Wed Jan 16, 2019 11:50 am
As you can see, IC 342 is a bit more irregular than M74. That suggests that IC 342 is more affected by star formation than M74. Either there is actually more star formation going on in IC 342 than in M74, or, alternatively, IC 342 is a less massive galaxy than M74 so that it more easily gets distorted by the extremely strong winds of massive star formation.

Ann
That's an interesting take on this. All I have heard so far goes the other direction: Gravitational "events" cause distortions, and then disruption of gas clouds, which then brings on bursts of star formation. I did not think that star formation could cause spiral arm distortions on the galactic scale. (Meaning that they could deform a spiral arm enough that it would be noticeable to an observer looking at an image of a galaxy at this scale.)
NGC 1313. Photo: Robert Gendler.
M101. Photo: Robert Gendler.





















The idea that galaxies get distorted from a lot of star formation is my amateur impression from looking at pictures of a lot of spiral galaxies and irregular galaxies. Irregular galaxies, as you know, are practically always small and low in mass, and they undergo a lot of star formation and become absolutely contorted because of that.

NGC 1313 is a smallish galaxy, somewhat halfway between a spiral and an irregular galaxy, and it is very distorted. Interestingly, it appears to be pretty much alone in its own neighbourhood, so its own shenanigans must have played a big role in making its shape so weird. (But I guess it just might have collided with, or been tidally disrupted by, a clump of dark matter passing by.)

M101 is of course a huge galaxy, but my impression is that it is lightweight for its size. Surely it must have been disturbed by interaction with another galaxy, but my guess is that its massive star formation has affected its shape, too.

M74. Isaac Newton Group of Telescopes.
Anyway, now that I look at the two pictures in my first post of galaxies M74 and IC 342 on my computer at home, the two galaxies look about equally distorted. Maybe that is because I can see the outer, low-luminosity arms of M74, while no such arms can be seen in IC 342.

But take a look at M74 again. See how regular its bright arms are, except for a strange "arc" at upper right, where the spiral arm "bends the wrong way". There appears to be a lot of star formation going on in the rims of that arc.

What caused the arc? Maybe a very powerful supernova, or even more than one supernova?

Ann
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