Starship Asterisk*

IC 1795: The Fishhead Nebula

Explanation: To some, this nebula looks like the head of a fish. However, this colorful cosmic portrait really features glowing gas and obscuring dust clouds in IC 1795, a star forming region in the northern constellation Cassiopeia. The nebula's colors were created by adopting the Hubble false-color palette for mapping narrow emission from oxygen, hydrogen, and sulfur atoms to blue, green and red colors, and further blending the data with images of the region recorded through broadband filters. Not far on the sky from the famous Double Star Cluster in Perseus, IC 1795 is itself located next to IC 1805, the Heart Nebula, as part of a complex of star forming regions that lie at the edge of a large molecular cloud. Located just over 6,000 light-years away, the larger star forming complex sprawls along the Perseus spiral arm of our Milky Way Galaxy. At that distance, this picture would span about 70 light-years across IC 1795.

<< Previous APOD

This Day in APOD

Next APOD >>

[/b]

One of the reasons for my fascination for astronomy is that I love the RGB beauty of starforming galaxies and RGB cosmic vistas that include nebulas and stars. Hubble palette images so rarely do anything for me. That is my hangup and my problem, and it says nothing about the quality of the individual Hubble palette image in itself.

I do know that Hubble palette images show us the degree of ionization of different parts of the nebula. But for me, since I can't much enjoy the aesthetic aspects of the picture, it is extremely important to be given an explanation as to why the ionization is the way it is.

When it comes to IC 1795, there ought to be a real story to tell. The Fishhead Nebula has another designation than IC 1795, or the brightest part of it has: it is called NGC 896. It is the only part of the Heart and Soul nebula complex to have an NGC designation. Why is this part of the Heart and Soul nebula complex so bright? What is known about the stars that light it up? Isn't there a Spitzer infrared image of it to reveal its stars? If the stars are so deeply hidden that none of our telescopes have managed to see into the depths of it, then what kind of educated guesses can we make about the stars inside? And what can be said about the star forming ability of this entire region?

Ann

Ann, I'm quite fond of creating these image swap pages these days so here is an image to use to compare the visible and infrared light from this area. You should easily find the Fishhead in the upper right glowing the most fiercely out of the entire complex in infrared. These were both APODs so it was just a matter of lining them up.

http://www.geckzilla.com/astro/heart_soul_swap.html

geckzilla wrote:Ann, I'm quite fond of creating these image swap pages these days so here is an image to use to compare the visible and infrared light from this area. You should easily find the Fishhead in the upper right glowing the most fiercely out of the entire complex in infrared. These were both APODs so it was just a matter of lining them up.

http://www.geckzilla.com/astro/heart_soul_swap.html

Thanks a lot, Geck, but I can't seem to do the swapping.

Ann

You should be able to simply click on the image and the swap will happen. If you have a slow internet connection then you may have to give it a moment, but it shouldn't take too long.

geckzilla wrote:You should be able to simply click on the image and the swap will happen. If you have a slow internet connection then you may have to give it a moment, but it shouldn't take too long.

Thanks! Clicking certainly worked!

Wow... the Fishhead Nebula is very bright in infrared light. But we still don't see any stars.

Ann

They are numerous and they are there. I suspect that they are so bright that the sensor was saturated, hence why they all seem to run together into a few big blobs, but I haven't gone to look at the raw data.

Awesome...have not seen this one before!!! Looks a bit like a Blue Gil, or other Sunfish.

Merry Xmas, or whatever to all our APOD friends!!!

:---[===] *

Looking over the catalog entries for the Fishhead, 30% of them are candidate young stellar objects... there are hundreds of baby stars hidden in there. Not just the bright spots, but on the whole head, like the blue area. This is impossible to read, but you get the idea.

The above exchange between Ann and geck shows that, even if at first glance something isn't all that appealing, looking at in a new way can be very rewarding.

This fish nebula wasn't atractive to me either Ann. It made me think of a dead tuna caught in a gill net.

But, now knowing that there are, as geck said, "hundreds of baby stars hidden in there," well, that makes all the diffence. We can appreciate this for what it is, even if we may not personally like what it looks like.

My favourite images of this region are by Ken Crawford and Don Goldman.

Ann wrote:One of the reasons for my fascination for astronomy is that I love the RGB beauty of starforming galaxies and RGB cosmic vistas that include nebulas and stars. Hubble palette images so rarely do anything for me. That is my hangup and my problem, and it says nothing about the quality of the individual Hubble palette image in itself.

Ann

I also share your view and I much prefer seeing narrowband images of planetary nebulae that have been mapped in a "natural" colour scheme. In my opinion, Don Goldman is the best narrowband processor, many nebulae have regions where both Ha and OIII overlap and his images show them perfectly combined. This is something that isn't properly represented in a "bicolour" processing scheme, which highlights the separate Ha and OIII data.

I know you've got favorites, starsurfer, but sometimes it seems like you spend too large a fraction talking about how you'd rather see so-and-so's work. Remind me not to invite you to dinner because you'd probably rather have grandma's cooking...

starsurfer wrote:My favourite images of this region are by Ken Crawford and Don Goldman.

Ann wrote:One of the reasons for my fascination for astronomy is that I love the RGB beauty of starforming galaxies and RGB cosmic vistas that include nebulas and stars. Hubble palette images so rarely do anything for me. That is my hangup and my problem, and it says nothing about the quality of the individual Hubble palette image in itself.

Ann

I also share your view and I much prefer seeing narrowband images of planetary nebulae that have been mapped in a "natural" colour scheme. In my opinion, Don Goldman is the best narrowband processor, many nebulae have regions where both Ha and OIII overlap and his images show them perfectly combined. This is something that isn't properly represented in a "bicolour" processing scheme, which highlights the separate Ha and OIII data.

I see little difference between Don Goldman's and Bill Snyder's images of this object, except for a minor shift in color balance. Both use the Hubble palette, which can't remotely be seen as representative of natural color. Both strongly separate Ha and O[III]. Not sure what you mean by "bicolour", since both use the same three narrow channels, and don't cross-mix them. Any image made from Ha, O[III], and S[II] will necessarily be far from natural color because Ha (656 nm) and S[II] (672 nm) both appear similarly red to our eyes. The only way to distinguish them in an image is to map one of them to a completely different color range.

Bicolor images are common, usually using Ha and O[III] filters. These are commonly mapped to red and green+blue, which yields a narrowband image that nevertheless approximates natural color (except for the stars).

A very Merry Christmas to all you Guys and Gals out there in deep space, as well as a Happy, Healthy and Prosperous New Year 2015. Cheers.

Pardon the non-scientific comment, but I had to get this one in:

this picture would span about 70 light-years across

That's gotta be the biggest fish that ever got away...

deb wrote:Pardon the non-scientific comment, but I had to get this one in:

this picture would span about 70 light-years across

That's gotta be the biggest fish that ever got away...

Hmmm... I'd say this one was caught.

Awesome photo. The name promises the head, but at these wavelengths we get the whole fish.

I feel a bit stupid now, as I had never before noticed the idealised heart shape in the Heart Nebula. I'd never known about the Fishhead Nebula either. To me, the Heart Nebula looked more like a realistic heart, with the Fishhead Nebula being the aorta shown sectioned. (Not that I'm an expert in anatomy.)

Nice APOD and great comparison images, geck.