Wikipedia:Reference desk/Archives/Science/2021 March 13

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March 13

How accurate are images of hubble space telescopes?

I learnt images by hubble space telescope are achieved by joining several shots. How accurate are images of hubble space telescopes? Mars 2020 images are 100% because they don't join pictures like HST does. Rizosome (talk) 10:16, 13 March 2021 (UTC)

These are not often using real colour, but different spectral bands mapped to colours to make a pretty picture. The chances are though if you looked as most of the targets yourself you would just see black,as they are so dim. I expect that the stitching is good though. Graeme Bartlett (talk) 11:29, 13 March 2021 (UTC)

That's usually the case, but sometimes HST takes pictures of the planets in our solar system and those are often quite close to what you'd see if you were near that planet. PiusImpavidus (talk) 17:54, 13 March 2021 (UTC)

I'm not sure what you mean by "joining images".

If you mean placing images next to each other to create a panorama, I don't think that happens. Please provide sources if you think that happens.

Astrophotography does join images using image stacking. (We have an article on image stacking but it is not one of our finest.) A number of exposures are placed on top of each other and added and/or averaged. This greatly enhances quality, for several reasons. E.g. the famous Hubble Deep Field is a stack of around 300 exposures (exact number of exposures used varies in different versions of the image). 85.76.71.130 (talk) 16:28, 13 March 2021 (UTC)

The field of view of the Wide Field Camera 3 is 2.7 arcminutes. If you need more than that, you have to stitch, so I assume its occasionally done. The artefacts you get from stitching are: (1) perspective error, resulting from a change in camera direction, but this is a minor effect as the field of view is tiny (and you can correct for it anyway); (2) parallax error, resulting from a change in camera position, but the observed objects are so far away that the effect is negligible; (3) temporal error, as the object you observe changes appearance between the images, but objects don't change faster than the time it takes a beam of light to travel across it, so the far-away objects large enough to need stitching can't change fast enough for it to matter.

BTW, Mars landers/rovers regularly produce stitched panorama pictures and they do show artefacts on nearby objects, like the lander itself. PiusImpavidus (talk) 17:54, 13 March 2021 (UTC)

Your own human vision also joins images from two separate sensors. --Amble (talk) 18:41, 13 March 2021 (UTC)

Be aware that for both Mars missions and Hubble, the images they release for general public consumption are usually not the same images that scientists use for serious research. All sorts of processing goes on to make the images look cool enough to use in a newspaper article, or as a desktop wallpaper. Joining images to form panoramas, combining monochrome images to make color or false-color images, warping them to compensate for a lens curvature, adjusting the gamma curves to make it more dramatic, etc, etc.

Scientists almost always use the raw images for exactly the reason you hint at. They don't want to spend time analyzing something only to discover that it's a glitch introduced during processing. ApLundell (talk) 20:13, 13 March 2021 (UTC)

Just a note, why are we bothering answering this question, given Rizosome's past behavior in questions on this desk? They haven't defined what "accurate" means, let alone the fact that images from Perseverance are, in no way, "100% accurate." There's no such thing as a "100% accurate" image, after all. --OuroborosCobra (talk) 21:53, 13 March 2021 (UTC)

Nonsensical questions can be boxed up. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:21, 13 March 2021 (UTC)

POSITRON HOLE Article no??

Electron - Positron = Electron hole - positron hole??

Cheers!108.25.84.35 (talk) 23:10, 13 March 2021 (UTC)

What is your question, exactly? --OuroborosCobra (talk) 23:15, 13 March 2021 (UTC)

If there is an electron and a positron and also an electron hole....is there also therefore ergo a positron hole?108.25.84.35 (talk) 23:19, 13 March 2021 (UTC)

Sure, there could be a positron hole in a system made of antimatter atoms. --OuroborosCobra (talk) 02:24, 14 March 2021 (UTC)

OK, So should I create the Positron Hole Page now? Do I get to name the anti-quasiparticle?108.25.84.35 (talk) 22:48, 14 March 2021 (UTC)

Depends. It might not pass the notability test. I don't think we've created enough full on antimatter atoms to have a repeating system where the idea of positron holes carries any relevance. Without that, it would be, at best, worth mentioning in the electron hole article. It might not even be worth doing that. --OuroborosCobra (talk) 00:32, 15 March 2021 (UTC)

Are you asking about holes in the Dirac sea, or electron holes in solid state physics? --Amble (talk) 02:04, 14 March 2021 (UTC)

No, thanks.108.25.84.35 (talk) 22:55, 14 March 2021 (UTC)

In hole theory, there is a fundamental symmetry between electrons and positrons. Just like a positron is an electron hole in the Dirac sea, one can build the mathematical model starting from the positron wave function, and then an electron is a positron hole. See the caption of Figure 12.4 here.  --Lambiam 07:57, 14 March 2021 (UTC)

An Electron is a Positron Hole?108.25.84.35 (talk) 22:56, 14 March 2021 (UTC)

Given an appropriate theoretical framework, as constructed in the cited source, it can be described as such, in precisely the same sense in which a positron can be described as an electron hole. It follows from the theory, as already established by Dirac, that they are each other's antiparticle, so the symmetry should not be surprising.  --Lambiam 14:03, 15 March 2021 (UTC)

So, there are two different things described as "holes", and they really aren't related to each other: The first is the conceptual "electron hole" in solid state physics, such as one sees in P-type semiconductors. In these cases, an electron-deficient dopant is used to create a situation where "electron holes" behave like positive electrons. These are NOT positrons, they are electron holes, and have nothing to do with antimatter. The other place we see holes is in Dirac sea theory, a means of explaining the relationships between matter and antimatter, where a positron is described as something like an "electron hole"; however the Dirac sea model has been largely replaced by better formulations of quantum theory, and no one really thinks of them that way. Despite using the same name; the electron holes in p-type semiconductors are NOT related in any way to the electron holes in the Dirac sea model. Hypothetically, if one were to create an anti-matter equivalent of a p-type semiconductor, then the holes could be called positron holes. Such a thing doesn't exist, and as such, don't go creating a Wikipedia article about it. --Jayron32 14:39, 15 March 2021 (UTC)

Thank you Jayron. If you would please entertain me for one more post. How can there be both an electron and a positron, which is an "anti-matter electron" but only one has a hole associated with it. Absence of electron is hole; absence of positron is not? This seems to go against my idea of "symmetry". Can you explain how a positron hole does not exist?108.25.84.35 (talk) 00:44, 17 March 2021 (UTC)

Positron holes don't exist because they can only exist in semiconductors made of antimatter, and such a beast doesn't exist in the first place. That theoretically semiconductors made of antimatter could exist, and that they would probably contain positron holes means nothing. Beside that you don't seem to possess one single crumb of a fragment of some reliable sources, so this article, when written, would not be in existence much longer than a positron hole. 2003:F5:6F14:2200:110B:6FF5:92CD:183B (talk) 13:49, 18 March 2021 (UTC) Marco PB