wimvb

Both answers are correct. Because DBE subtracts uneven sky background, you end up with less captured light (less background light, not subject light), but the associated noise is still there. The statistics of the image have changed, and the new STF is a bit more aggressive, revealing the noise that was always there. You can adjust the permanent stretch so as to avoid the prominent noise shown by the stf. In other words, avoid using the new stf as a permanent stretch.

There was one, a King cobra, on the loose in a Stockholm zoo recently. So this would actually make a lot of sense. 😁

As Dave says, when the noise is mainly from the captured light, it will diminish as you collect more data, either through longer exposures, or through more exposures. But if the noise is dominated by read noise from the camera, then stacking more subs won't help. That's why exposures need to be long enough. In practice, if you see horizontal or vertical bands in the single exposures when you stretch them, this is most likely read noise, and you need to increase the exposure time. The amount of read noise depends on the camera and its settings. Modern cmos cameras have such low read noise that single second exposures can be long enough. Dslrs and some cmos have higher read noise and need longer exposures. Unfortunately there is no single, universal correct exposure time, and you will need to experiment.

We have one less. 😁

2MASX06155357+7812021 From the 2MAS extended catalogue The 2MASS Extended Catalog (2MASX) It's also in GAIA DR3 (GAIA Data Release 3)

I checked for any galaxies in Vizier in this area, and found several that are not in your image, but not one correspondig to TGC 1. Weird, because your candidate isn't that faint, and DSS shows more detail than in your image.

An update on imaging this very faint galaxy. PixInsight has several useful tools for data and image analysis. One of these is the 2DPlot script (Scripts -> Utilities). This script allows one to create an intensity profile along a line, either horizontal, vertical or diagonal in a monochrome image. I used a linear stretch on a copy of my luminance master, meaning that I brought in the black point and white point, without touching the mid point slider. This means that between the clipping points, the data is still linear. This is what the script came up with. The right hand side shows a zoomed in section of the luminance image, with the position of And XXX marked with an ellipse. The horizontal line is where the intensities were measured, and the panel on the left shows the pixel intensities across this line. Not that the profile is for the whole image width, not just the zoomed in section. The position of the galaxy is marked by a red line. This line covers the same section as the ellipse in the image panel. There is a very slight increase in intensity where the galaxy is supposed to be. But since the surface magnitude of And XXX is 26 Mag/arcsec2 or fainter, this hardly clears the background level and noise floor. This project was never intended to result in a pretty picture. Rather I wanted to know if it is possible to image faint dwarf galaxies with moderate amateur equipment. I also wanted to show some of the cool physics that is going on in what is essentially our backyard of the universe.

It is a galaxy, snd it’s a bit strange that it’s not in any galaxy catalogue. So let’s name it tgc 1 (Tomato Galaxy Catalogue, 1st entry).

Very nice! Here's the mysterious galaxy, I believe http://simbad.u-strasbg.fr/simbad/sim-id?Ident=2MASS J06213825%2B7813105 Edit: no, that's not it. It doesn't turn up in aladin either

Interesting. Now, of course, we need an explanation for this. Rippling waves come to mind. But then we need forces (winds) that create these waves. My guess is that features such as these are created by the stellar winds pushing matter before them. The matter itself can sometimes be ejected by stars. For example planetary nebulae that have shell like structures. Over time, such shells expand and become less pronounced. The original form, having the same origin, is still visible, although washed out and less regular. Add to this the fact that the human mind is wired to see and seek out patterns, in order to make sense of all the visual stimuli from our surroundings.

In my opinion, M42 is about the drama and the contrasts. I like the aggressive version. But as Olly remarked, broadband colour does a lot to lift the details. It's these details that add to the drama. Hopefully we get to see a colour version of your image.

Shorter exposures does NOT equate to less noise, because cameras have read noise, independent of exposure time. Longer exposures = less noise, or higher signal to noise ratio ("more signal per noise"). In theory, every time you double the total exposure time you already have, you cut the noise to 70%, as long as you've exposed long enough to drown the read noise. The point of diminishing returns is determined by perseverance, or just simply by you saying "that does it for me". When we progress in astrophotography, most of us (including myself) go from shooting multiple targets per night to shooting multiple nights per target.

Interesting target, the WLM galaxy. Unfortunately it’s a bit too low for me. At 60 degrees north, the galaxy clears the horizon by 15 degrees at best. I have a forest across a field to the south, so it would clear those trees by maybe 10 degrees. My view is also a bit limited by trees on my own property, which means a clear view only about 2-3 hours at best per night. I generally avoid imaging objects which have a declination less than zero. Andromeda XXX has a surface ”brightness” of 26 Mag/arcsec2, well below my sky quality. The stars are brighter but very small. They didn’t show up until after 8-9 hours of total integration time. You can find more information here https://aladin.unistra.fr/AladinLite/?target=00 36 34.901%2B49 38 48.00&fov=0.28&survey=P%2FDSS2%2Fcolor

Well, that turned out to be a dud. I spent an unexpected clear night on ngc 147 and couldn't even reveal the box-like outer regions of the galaxy that show in the wide field image of my previous post. There's no way I could ever come close to catching the tidal stream itself.

Thank you, Rodd. How dark is your site? According to Clear Outside, the sky quality where I live is supposed to be 19.4 Magnitude, or Bortle 6. But at best it is closer to 20.4 Magnitude, Bortle 5.

Even with short exposures you will still have field rotation. The field will rotate 15 degrees for every hour you spend on a target. You may not see much of that in single subs, but you will need to crop a major part of your stacked image. One way to minimize the effect of field rotation is to image over multiple nights. Say you have 4 hours to spend from 8 pm until midnight. You choose 4 targets. The first hour you image target 1, then one hour on target 2, etc. The next night you do the same again. Between 8 and 9 pm you image target 1, between 9 and 10 pm target 2, etc. As long as you make sure that you image target 1 in the time slot between 8 and 9 pm, target 2 between 9 and 10 pm, you can limit field rotation. Of course, you will need multiple nights of clear weather, and you will need to make sure that your camera angle always is the same. The alternative is that you rotate the camera during a long session. But doing so, you may need flats for every change in angle.

Thanks! And now I'm chasing the very faint tidal stream that supposedly exists around ngc147. I don't know if I'm bold or just foolish, because no one has imaged that before. And it may be even fainter than And XXX. https://ui.adsabs.harvard.edu/abs/2013ApJ...776...80M/abstract

Thanks, Lee. The ifn is actually a lot brighter than the galaxy, and normally you wouldn't be able to discern one from the other. It is the combination of the slightest increase in brightness over the background and identification of those 8 individual stars that allowed this to be identified as a galaxy. This truely is a faint fuzzie.

Thanks, Geof. This is the faintest object I have ever tried to capture. I was surprised to discover that it has a surface brightness of only 26 Mag/arcsec2. I would never have expected that I could get this deep from my location. My best sky darkness so far was 20.4 Mag/arcsec2, and that was during mid winter.

A month ago, I tried to image a faint Andromeda dwarf satellite galaxy, And XXX / Cass II. This galaxy was discovered as late as 2013 during a deep sky survey of the Andromeda galaxy region. At the time that I posted my attempt, I had collected 40 minutes of Luminance data that showed no trace of this small companion to M31. One month and 30 imaging hours later, I may have caught something. And XXX / Cass II is the thirtiest satellite galaxy to M31. It has diameter of only approximately 1600 ly (540 pc). The galaxy was discovered and characterised based on only 8 of its member stars. Although the galaxy has an absolute magnitude of -8, its surface brightness is only 26 mag/arcsec2, making it almost impossible to detect. I believe that this image is the first obtained by an amateur astronomer. Technical data: Equipment: SW 190MN and ZWO ASI294MM camera with Optolong LRGB filters Exposures: 483 x 3 minutes L frames (24 hrs in total), and 71 x 5 minutes (almost 6 hours) RGB Processed in PixInsight You don't see it? It's there allright, hiding in plain sight:

And of course, there's also a roe's head in the image.

I think we should keep it biological, reptilian.

Actually, the snake's head near the top left corner is [DB2002b] G93.46-12.63 The Ha cloud next to it doesn't have a name, afaIk. The appendage above HD 209919 is PLCKECC G092.83-11.03. Its head is on the almost horizontal line RA 22h 8m I agree that the bright reflection cloud should have a popular name. [DB2002b] G93.46-12.63 doesn't quite roll off the tongue. Simbad did not find a white dwarf candidate in or near the presumed PN.

That's why I made my previous comment about having difficulties interpreting the hst image. But I guess you know my standard reply to this, Göran: we need more data . In this case broadband and luminance data.

I didn't have time to delve deeper into this. The HST image doesn't really match with Göran's image, at first glance, but this may be due to different filters being used. This is definitely going on the to do list, but not this side of New Year. The target is behind my obsy walls.