Starship Asterisk*

by **johnnydeep** » Thu Nov 23, 2023 1:34 pm

sc02492 wrote: ↑Thu Nov 23, 2023 10:03 am
Lasse H wrote: ↑Wed Nov 22, 2023 1:32 pm I think I would appreciate this "hidden galaxy" a lot more, and also appreciate the efforts behind revealing its appearance, if I could also be shown what it looks like when it is hidden--that is what it looks like before filtering and manipulating noise and signal.
Lasse, sorry for the late reply. You are making a good point. One way to answer your question would be to compare the relative brightness of IC342 against a more familiar target like M81 (for instance) by using a single subexposure, taken at 60 seconds at the same camera settings (ASI294MM, gain, offset, and chip temperature), same telescope (FSQ106N), and same conditions (new moon, same altitude) and then the same pre-processing calibration and post-processing curves stretch. I would have to dig into my old data to see if I have something comparable for M81 or M101. When I have more time I will try to find this and let you know. The comparison could be done visually but also by measuring flux in software like MaximDL. I can do all of that, but it will take a little time.

For those few commenters who are critical of my image of IC342, please understand that this is a difficult target to capture with a 4 inch scope in a Bortle 4-5 zone, with straight LRGB filters (no Ha). That was part of the fun and challenge for me, and it provides inspiration for those who might want to try it themselves. Unless you have actually tried to capture this particular target, you won't necessarily appreciate what goes into the effort. Based on the numerous positive comments that I received yesterday, a lot of viewers enjoyed the result and learned something about how dust in the galactic plane can affect the appearance of extra-galactic targets like IC342.

All of the images that you see on APOD reflect a great amount of effort, both on the part of the astrophotographers and the APOD editors. It's easy to be arm-chair critiques of this kind of work, but remember that it's a privilege for us to have this resource available to us.

Happy Thanksgiving to all.

Steve

Steve Cannistra
www.starrywonders.com

Amen!

by **sc02492** » Thu Nov 23, 2023 10:03 am

Lasse H wrote: ↑Wed Nov 22, 2023 1:32 pm I think I would appreciate this "hidden galaxy" a lot more, and also appreciate the efforts behind revealing its appearance, if I could also be shown what it looks like when it is hidden--that is what it looks like before filtering and manipulating noise and signal.

Lasse, sorry for the late reply. You are making a good point. One way to answer your question would be to compare the relative brightness of IC342 against a more familiar target like M81 (for instance) by using a single subexposure, taken at 60 seconds at the same camera settings (ASI294MM, gain, offset, and chip temperature), same telescope (FSQ106N), and same conditions (new moon, same altitude) and then the same pre-processing calibration and post-processing curves stretch. I would have to dig into my old data to see if I have something comparable for M81 or M101. When I have more time I will try to find this and let you know. The comparison could be done visually but also by measuring flux in software like MaximDL. I can do all of that, but it will take a little time.

For those few commenters who are critical of my image of IC342, please understand that this is a difficult target to capture with a 4 inch scope in a Bortle 4-5 zone, with straight LRGB filters (no Ha). That was part of the fun and challenge for me, and it provides inspiration for those who might want to try it themselves. Unless you have actually tried to capture this particular target, you won't necessarily appreciate what goes into the effort. Based on the numerous positive comments that I received yesterday, a lot of viewers enjoyed the result and learned something about how dust in the galactic plane can affect the appearance of extra-galactic targets like IC342.

All of the images that you see on APOD reflect a great amount of effort, both on the part of the astrophotographers and the APOD editors. It's easy to be arm-chair critics of this kind of work, but remember that it's a privilege to have this resource available to us.

Happy Thanksgiving to all.

Steve

Steve Cannistra
www.starrywonders.com

by **orin stepanek** » Wed Nov 22, 2023 8:59 pm

If memory serves; we had one called hidden several years ago called
hidden!

by **Ann** » Wed Nov 22, 2023 2:51 pm

Christian G. wrote: ↑Wed Nov 22, 2023 1:00 pm To further bring this galaxy out of hiding, here's another very nice and recent image, finely detailed:

Thanks for posting Chris Peterson's recent image, Christian. It's very fine image, and in my book, it is better than the APOD. Not the the APOD isn't fine, too.

IC 342 is a "perfect Sc galaxy", similar to M74. It has a small yellow core and long, elegantly curved arms, which are often full of blue stars and pink nebulas. IC 342 and M74 are both grand design galaxies too, with just two major arms. (Even though IC 342 isn't the best example of a grand design galaxy, since it does seem to have some extra arms and spurs, too.)

IC 342: Hidden Galaxy in Camelopardalis.
Image Credit & Copyright: Steve Cannistra

: IC 342. Credit and copyright: Chris Peterson

Note how similar IC 342 is to M74:

: M74, the 'perfect' Sc spiral galaxy. Credit adn copyright: Adam Block.

Onde difference between IC 342 and M74 is that M74 is a *pure" unbarred Sc galaxy, whereas IC 342 does have a small bar. Note the dust lane that seems to cross the center of IC 342.

Ann

by **Chris Peterson** » Wed Nov 22, 2023 2:24 pm

Lasse H wrote: ↑Wed Nov 22, 2023 1:32 pm Thank you, Steve and Christian! I think I would appreciate this "hidden galaxy" a lot more, and also appreciate the efforts behind revealing its appearance, if I could also be shown what it looks like when it is hidden--that is what it looks like before filtering and manipulating noise and signal.
Someone must have seen first, and become surprised that it was there! How little do you see of it when it is hidden?

Both Steve's image and mine above are pretty accurate "true color" representations. This is what it looks like visually (if our eyes were simply more sensitive). Were it not behind dust, it would be much brighter, which is impossible to show in an image, but visually we'd see something in our northern skies not unlike the LMC in the south. And photographically, we'd lose the striking reddish coloring, which is a consequence of dust reddening. The dust blocks most short wavelength light. Look at all of the HII regions in the arms of IC 342. There is a lot of new star formation going on. Which means there are lots of hot, blue stars. But we don't see them. The dust almost completely hides them. The few blue stars we see in these images are foreground objects, in front of the dust. Without the dust, I think this galaxy would look a lot like M 101 (below), which also has lots of star formation going on in it.
_

by **Lasse H** » Wed Nov 22, 2023 1:32 pm

Thank you, Steve and Christian! I think I would appreciate this "hidden galaxy" a lot more, and also appreciate the efforts behind revealing its appearance, if I could also be shown what it looks like when it is hidden--that is what it looks like before filtering and manipulating noise and signal.
Someone must have seen first, and become surprised that it was there! How little do you see of it when it is hidden?

by **Christian G.** » Wed Nov 22, 2023 1:00 pm

To further bring this galaxy out of hiding, here's another very nice and recent image, finely detailed:

by **sc02492** » Wed Nov 22, 2023 12:09 pm

Lasse H wrote: ↑Wed Nov 22, 2023 11:48 am
I have nothing against this galaxy, but I would like to see just how it is "hidden". Each time the caption claims it is only glimpsed through the veil of stars, gas and dust clouds in our galaxy. The photos do not really show this veil of gas and dust---to me it comes forth as quite visible and similar to other photos of galaxies.

Lasse, I tried to explain this in the description on my website. The "Hidden" aspect is a term that originated from the days of visual astronomy. When I myself first attempted a visual observation of this galaxy many years ago, at a reasonably dark site and a large aperture Dobsonian, I could hardly detect it (in comparison to M81 for instance). It is really very difficult to appreciate visually. With astrophotography techniques (including film in the old days), it is much easier to increase the signal above the noise to allow detection, although even so it is a relatively dim target. I even used more blue filter exposure on this image, and yet it is still reddish/brown in overall color, due to preferential extinction of blue light as it passes through Milky Way dust.

Steve

Steve Cannistra
www.starrywonders.com

by **Lasse H** » Wed Nov 22, 2023 11:48 am

Similar photos of this galaxy have been published eight times (see Archive!); always with the title "IC 342: Hidden Galaxy".

I have nothing against this galaxy, but I would like to see just how it is "hidden". Each time the caption claims it is only glimpsed through the veil of stars, gas and dust clouds in our galaxy. The photos do not really show this veil of gas and dust---to me it comes forth as quite visible and similar to other photos of galaxies.

by **APOD Robot** » Wed Nov 22, 2023 5:05 am

IC 342: Hidden Galaxy in Camelopardalis

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 star forming regions along spiral arms that wind far from the galaxy's core. IC 342 has 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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