andrew s

Well done @ollypenrice what it needs is some diffraction spikes on the bright stars to add impact and framing 🤣 Regards Andrew

Interesting with lots of maybe and ifs and buts. If darkmatter is a particle and if it is its own anti particle then in the much denser early universe it could have got dense enough for there to be a significant number of collision of dark matter particles to annihilate and power a dark star. If such a process was going on now in our galaxies dark matter halo we should see a background glow. I am not aware of any such detection so it seems to be too diffuse. Regards Andrew

Yes it can accumulate in galaxies but it is still very dilute compared to stars and planets etc. As I said about 1/9 Ceres mass in the solar system. While personally fun wild speculation won't actually give you much insight. Regards Andrew

You miss two key points. The average density of matter is very, very low. We only notice it when it's concentrated into stars, planets and clouds etc. Which brings me to my second point. While dark and normal matter are effected by gravity in the say way dark matter can't concentrate as normal matter does. To concentrate matter needs to lose angular momentum and kinetic energy. Normal matter does this by emitting electromagnetic radiation giving us some of the most spectacular sights e.g. accretion discs. Dark matter can't do this so remains diffuse. Regards Andrew

1) Yes lensing is used to compute the distribution of matter (normal and dark) in galaxies. 2) If our measures are that far out I think our predictions on binary stars motion would be way off but they seem ok. Look here for a bigger example. 3) the mass of dark matter in the solar system is estimated to be about 1/9 the mass of Ceres. I have no idea what your last sentence means. We currently don't know what dark matter is. Regards Andrew

Never looked at this thread but as I scrolled past a thought hit me. Post apocalypse that is all we might have left. Strange how these things arise. Regards Andrew

I think most astroimaging packages have them built in. I would look at the free astroimagej first. @vlaiv will be along to confirm if it has one. Regards Andrew

Sorry we at cross purposes then. Your statement above seemed to me to be about under sampling. Regards Andrew

Absolutely, agree. By definition if you under sample the you are losing higher frequencies! If your combined system optics/mount/seeing is capable of delivering 1 arc sec and you under sample you will lose resolution and information. A pure star field may look the same as your just looking at gaussian images which scale. Look at a planet, nebula etc with 1 arc sec detail. and they will be different. Regards Andrew

It's difficult due to the difference in stretch but to me the whole lower image looks grainy. This is more obvious in the faint outer regions. It may be due to the noise and or stretch but how can you clearly delineate the data from the noise. You can't, especially in the areas where the signal approaches the noise floor. Regards Andrew PS I assume you accept there are differences in the leaf picture given your earlier reply. The same maths applies to both.

Well I can see differences in these two images. So that seems to contradict what you just posted. However, I won't continue. Regards Andrew

Musing about all this, the artifacts in the under-sampled leaf when stacked and processed could easily give the impression of enhanced detail if you don't have a higher resolution reference image. One way to look at this is your seeing/guiding/optics need to be spatially band limiting your system. This gives some good examples of the problems you can get in normal photography if you under sample. It says this "Many digital camera sensors— especially older cameras with interchangeable lenses— have anti-aliasing or optical lowpass filters (OLPFs) to reduce response above Nyquist. Anti-aliasing filters blur the image slightly, i.e., they reduce resolution. Sharp cutoff filters don’t exist in optics as they do in electronics, so some residual aliasing remains, especially with very sharp lenses. The design of anti-aliasing filters involves a tradeoff between sharpness and aliasing (with cost thrown in)." Astro imagers have the atmosphere and their mounts and optics to do the filtering! My two pennyworth would be it's better to slightly oversample than risk under-sampling. Regards Andrew

Not sure exactly what your trying to show but on my device the top leaf is much sharper by eye than the lower one which also shows artifacts. Regards Andrew

Lots of misunderstanding of each other. For example, a cameras are areal detectors normally square but give a single "point" output per pixel. Another would be a signal varying in time compared with one in space with 1/time frequency compared to 1/distance a spatial frequency. Best to follow your own proposal and call it an unsatisfactory no score draw. 😊 Regards Andrew

Maybe, as you said, it's too different a use case. In high resolution spectroscopy you have one long exposure image. So stacking is not normally an option. In the text he does discuss the issues you raise but obviously answerers them in his context. Regards Andrew

Don't feel you need to do this unless you want to. However, if you do you can't use gaussian noise alone as rtn is not gaussian. Best to use the noise from a small pixel CMOS camera. Regards Andrew

Along with the flying pigs. 😊

I am surprised at such a quick dismissal. Christian is a careful worker and I respect his opinions as I do yours. However, given the speed if your response I assume you have looked at his algorithm before and compared the results. If so could you share the results. Regards Andrew

One area of noise which has grown in importance with small pixel CMOS cameras is random telegraph noise. If it's been covered above please forgive my not reading the whole thread. I have not seen it discussed much but it can be the dominant noise. C Buil discusses it on his site and give an algorithm for reducing it in over sampled images here in section 6 (wrongly labled as 5) It is in French but Google translate does a fair job. There are also some English discussion on it in the CMOS camera reviews. Here for example. Regards Andrew Note his data refers to the native camera bit depth not 16 bit unless it is a 16 bit camera.

As it makes up some 68% of the mass/energy of the Universe we would not see the gravitationally formed structures we see today if it were your proposed negative mass. Regards Andrew

I think this is one of the very few places on the web, or elsewhere come to that, where one can have a civilised conversation on science related topics. It has a concentration of science aware individuals with a broad range of knowledge and skills and it's all the better for that. Regards Andrew

Strictly, it also has to be point sampled. This is not the case with areal sensors like CMOS cameras. Regards Andrew

The second law is a good theory that makes accurate predictions within its domain. It is limited to closed systems and is statistical in nature. Our very existence show it is not valid for open systems. Regards Andrew

It worth reminding ourselves just how far we have come. Simple observations are the Sun, moon and stars go round the earth but we now know better. What causes an apple to fall to earth is the same as that which keeps the planets in orbit and the galaxy turning. Gravity is not a force but a curvature of spacetime. Nuclear fusion powers the stars and we are literally star dust. Solid objects are 99.9% empty space. Obvious now? Regards Andrew

I don't know not really looked into it. Regards Andrew