Friday Galaxy Blogging : IC 342

You mean IC 342 in the text there, not 642.

Numbers, schmumbers.

I'm amazed that they could record a picture of such clarity from a terrestrial telescope. Is there any indication of how long the camera's aperture had to remain open for them to record the picture?

raj,

It's a relatively nearby galaxy (~ 3.4 megaparsecs = 11 million light years), which makes it a lot easier to see the detail.

My (wild, off-the-cuff) guess would be exposure times of 5 minutes in two or three filters, plus maybe 20 minutes in H-alpha (I'm guessing the pink in the image comes from hydrogen emission).

What Peter said.

This image was made using a big 'ol widefield imager on the 4m telescope. To get really beautiful images of nearby galaxies, you need wide field imagers, as they can be pretty huge on the sky.

The pinkish image assuredly is star forming regions, as they follow the right pattern and are in all the right places. I'm not sure if it's strictly from Halpha filters, or if the equivalent widths of the lines in those regions are just huge enough to dominate the light. The press release is short on details as to exactly which filters were used.

Peter & Rob:

Thanks for the information. I'm just amazed that they could correct for the "image blur" which would be caused by the movement of the camera as well as they obviously did.

I downloaded the detailed jpeg image earlier.

At the risk of being considered trollish here, I'll recount a story from my childhood. When I was 13 or so in the early 1960s, I and my boy scout troop went on an overnight canoeing trip on the Whitewater Canal in Indiana. During our overnight stay in Metamora, Indiana, a number of us boy scouts went up to the point at which that canal passed over another canal. It was very dark--no light pollution--and we could see the stars. The firmament. It was astounding. There was little talk as we amazed ourselves with the view of the stars. I'm not a big fan of what religion has become, but it is almost as if we were looking at the eye of god.

raj,

The image was probably taken with the aid of an autoguider: a relatively bright star just outside the image you see was observed at the same time with a smaller, high-speed camera (taking an image many times a second). A computer monitors the position of this "guide" star; if it shifts, the computer sends commands to the telescope to adjust its pointing slightly to compensate.

Is it possible to use adaptive optics on such a wide field? Assume the camera has enough pixels to resolve a wide field at better than normal atmospheric limits.
Is the pink false (in a digital imaging sense) color? I.e. could any concievable filter directly produce the colors in the image?

bigTom,

Is it possible to use adaptive optics on such a wide field? Assume the camera has enough pixels to resolve a wide field at better than normal atmospheric limits.

Not at the moment, no. Currently, adaptive optics is limited to correcting regions of about half an arc minute in size; the image here is about 34 or 35 arc minutes across, I think (just over half a degree, in other words). Even future instruments using so-called "multi-conjugate adaptive optics" won't do more than about an arc minute across.

Is the pink false (in a digital imaging sense) color? I.e. could any concievable filter directly produce the colors in the image?

The pink is probably representing emission from hydrogen, which actually is sort of pink when seen by the human eye.

It wasn't adaptive optics.

But let us not forget that you don't need really, really find resolution to get amazingly pretty pictures on this scale. The camera that they were using is MOSAIC, which has an 8,000 by 8,000 pixel resolution. I'm not sure the exactly scale of these pixels, but it's probably such that the blurring of the atmosphere will spread a typical star out over a few (say 4ish) pixels across. Given that, the image is still going to look perfectly sharp on any computer-monitor-sized reduction!

The HST PR machine has done astronomy a great service by putting astronomy in the public eye so much. However, they're probably guilty of overstating their case, as people now have the impression that it requires Hubble to get any good looking image at all. For a distant galaxy, yeah, you'd need adaptive optics or Hubble to get any kind of resolution. But for nearby galaxies -- images like this are entirely feasable from the ground, and long have been.

-Rob

Personally, I'm stunned by this image. I've gotten a bit jaded by all of the HST pics, so I thought this was 'just another pretty galaxy' when I first saw this image. When I read that it was IC 342, my jaw dropped. That's a really difficult galaxy to image well - it's close, so you need a wide field imager, but it's also semi-hidden in the glare and dust of the Milky Way. If it was anywhere else in the sky, it would be a major showpiece for small telescopes.

I've actually taken a picture of IC 342. It was years ago, and I didn't have a wide filed imager, so it's a mosaic of nine images captured with an 'I' filter on the Table Mountain Observatory 24 inch. (I've got that mosaic somewhere...but it might be on an old 8mm tape somewhere. Hmm....) In any case, it's not nearly as cool of an image as this.

Kudos to the team that created this one...I'm impressed! (Oh, and thanks to Rob for sharing it here. I think I saw this on APOD, but I don't think I'll get tired of this image anytime soon!)