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Wikipedia:Reference desk/Archives/Science/2020 June 23

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June 23

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Casseiopeia (constellation)

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In the article List of stars in Cassiopeia the stars are shown as having a distance in light years. When I click through to (some of) the individual star articles, the distances are significantly different. Is this an error or is there a factor I am unaware of to take into account? EG Gamma Cassiopeiae says distance 550 ± 10 ly yet the 'List of...' says 613 ly. -- SGBailey (talk) 10:30, 23 June 2020 (UTC)[reply]

Wow, how the months fly by ... it seems like only last week, but it was actually six months ago when I quipped:
Yeah - so if you're looking for an almanac or all-sky survey, Wikipedia is categorically the wrong place to pull your numerical data from. Just this week I was watching science-talks out of Keck, so my mind is a little bit pre-conditioned... but if I needed an all-sky catalog, I would go straight to Pan-STARRS, or MAST, or the USNO - (comically, the entirety of the USNO digital products have been "offline" for most of FY2020 due to some grumbling about our government budget or technical reasons or manpower shortages - ... have we mentioned that we're in a literal national emergency these days, and that the effects have been very specific and profound? I had to go to an unofficial almanac to find the true solstice last week... and it pained me...)
...Those horrible data catalogs are the ones you want to use, if you actually need the values for any actual purpose other than general interest. Eschew using data that you copy off of Wikipedia: while our encyclopedia is great for general interest, our anonymous-editable format and our volunteer curator-editor culture are simply unsuitable for data retrieval questions.
Anyway, if these sources are too technical, you might find a software package like Starry Night or the free software KStars much easier to use: you can just click on the star or deep-sky-object, and the graphical interface will pop right up with a full catalogue of data on it. Those are essentially front-ends to PPMXL, a catalog of scientific merit, but of course the first line of the paper that introduces PPMXL will refer you straight back to the US Naval Observatory catalog....
Nimur (talk) 15:06, 23 June 2020 (UTC)[reply]
Until not that long ago star distances from us were notoriously fuzzy compared to say paper road maps. Latitude or longitude was good to what would be several feet on Earth at worst but distances were horrible, though error wasn't too bad for the highest parallaxes like alpha Centauri. The cosmic distance ladder has since improved and Gaia spacecraft data starting from the mid 2010s is asymptotically approaching 10 percent at large fractions of the galaxy width and much better for close stars. Sagittarian Milky Way (talk) 15:52, 23 June 2020 (UTC)[reply]
I would beg to differ, or at least to qualify that, with a "citation-needed" - the field of stellar spectroscopy has a long history; measurement of the spectrum is - and has historically been - the provincial home for the most precise and accurate numerals ever measured, among all other scientific pursuits. (Hey, did I just mention that I've been watching videos from Keck this week? Here is Spectroscopy: How Astronomy Really Gets Done, a video lecture by John O'Meara, the Chief Scientist of the Keck observatory).
Yeah - so the conversion from redshift, or "z-index", to units of conventional distance is a little more complicated - but it is both accurate and precise - extraordinarily so, in the scientific sense of those words - though it is parameterized - by Hubble's law. The precise numerical value of the parameter - particularly, the Constant - has a notorious history - but it's not "fuzzy." The word that I would use, actually, would be "sharp," because we use sharply defined discrete spectral lines like the examples shown in our article. "Fuzzy" is the antithesis of real astronomy - we can regale you with everything you need to know about what causes "fuzziness," and how we have built up the entire modern discipline of optical astronomy to, um, resolve that.
If I may put a more sharp point on my commentary - why are you trying to measure distance-to-stars in the wrong units? Real astronomers don't use meters, and they don't even use "light-years," because those are useless units. Were you planning to walk, proverbially or literally, from "here" to "there"? ... Well, you can't. So, why would you measure distance to a star in the same way that you measure distance to the corner store? It's a dumb way to measure, and it's no wonder that when you get right down to the details, you find them confounding. There are confounding factors about expansion; about apparent motion; about reference frames; about relativity. There are confounding factors about time-scales and distance-scales and weirdnesses of gravity that only matter to objects-the-size-of-universes. If you can't evolve your brain to think different about distance, you won't ever really be able to grok distance as it applies to astronomy - and there will never exist any data-table of stellar distances that shall be complete- or consistent- enough to be useful to you.
Nimur (talk) 16:13, 23 June 2020 (UTC)[reply]
Stars are not subject to cosmological redshift (galaxies are), so you can't measure their distances using spectroscopy. The most precise way to measure stellar distances is through parallaxes, and, exactly as SMW said, this has only recently become possible for a large number of stars, with Gaia being the current gold standard. In the German article, the value of 550 Lyr quoted in the question is sourced to the Hipparcos satellite; I don't know where the other value comes from. --Wrongfilter (talk) 16:30, 23 June 2020 (UTC)[reply]
Well, that's not correct either - the first measurements of optical doppler-shift were on stars. I think you are conflating all red-shift with red-shift that is unique to the expansion governed by Hubble's law, ... but that is a categorical error. Any relative motion - any at all - can provide a measurable doppler shift.
Nimur (talk) 16:37, 23 June 2020 (UTC)[reply]
That is an error that I would never make, in fact I can get quite angry when cosmological redshift is associated with relative motion at all. Stellar redshifts are caused by the Doppler effect, which means you can infer their line-of-sight velocity from them, but not their distances. And, if you remember, the question was about distances. --Wrongfilter (talk) 17:44, 23 June 2020 (UTC)[reply]
As an aside - for anyone who wants to follow up on my strong claims about accuracy and precision, here's some further reading material:
  • Daniel Rothbart and Suzanne W. Slayden, "The Epistemology of a Spectrometer," Philosophy of Science 61, no. 1 (Mar., 1994): 25-38. Available online.
  • Measurement in Science, from the Plato Encyclopedia of Philosophy.
Both of these provide a fine overview on the role of precise and accurate measurement - and the unique role of astronomical spectrometry in the development of the modern theory of scientific knowledge. In particular, optical astronomical spectroscopy plays a very real role in the history of science and the discovery of the fundamental physical constants, which are the absolute minimum set of data-entries that are necessary to quantify everything that we, as a species, know. These numbers are the most accurate and precise measured quantities that we have - they must be - because every other measurement we can possibly make is deeply and inherently tied to these measured properties of the universe.
Nimur (talk) 16:37, 23 June 2020 (UTC)[reply]
Sure for a long time we could measure star redshift and peculiar velocity and parallax to tiny, tiny amounts of nanometers and tiny fractions of c and small pieces of arcseconds, great but the star distances I remember from old books as a kid were not that great beyond several hundred light years and that's a lot of the naked eye prominent stars. I remember distance estimate differences of 50 or 100 percent for Deneb and still significant by Earth standards for Antares, Betelgeuse, Alcyone, Polaris, large differences for the nearest and furthest galaxies though those are pretty good now with the Hubble constant being pinned down and all. Star distances from the right sources are pretty good now too, something halfway across the galaxy will be a first order approximation or so but who cares, they're dim and numerous. Sagittarian Milky Way (talk) 17:16, 23 June 2020 (UTC)[reply]
As I recall there weren't enough rare stars with good absolute magnitudes with some effect on knowledge of stellar evolution and the Gaia has helped greatly with this. Sagittarian Milky Way (talk) 17:18, 23 June 2020 (UTC)[reply]

So to summarise: "It isn't surprising that they are different in Wikipedia, and unless I want to spend significant effort tracking down reliable sources, I should just put up with it." -- SGBailey (talk) 20:47, 23 June 2020 (UTC)[reply]

Isn't that generically true for all info on Wikipedia: "It isn't surprising that some information on Wikipedia is inaccurate, and unless someone volunteers their effort tracking down reliable sources, you have a choice: either put up with it, or be that volunteer."  --Lambiam 10:11, 24 June 2020 (UTC)[reply]

Smartphone cameras

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Will smartphone cameras ever be able to produce DSLR Quality photos with the technologies available and being developed? And what are the main limitations of smartphone cameras over DSLR? Clover345 (talk) 21:21, 23 June 2020 (UTC)[reply]

Sensor and lenses in a smartphone are so much smaller and simpler, for example a full-frame 35mm sensor measures 864mm2 while a 1/1.7” smartphone sensor only measures 43mm2 ([[1]]). And the lenses in a smartphone mostly are one, two or three (maximum today five), while a professional objective for reflex cameras can consist of fifteen or more elements (the 'single' in DSLR doesn't mean that the objective consists of one single lens, but that there is only a single lens system serving both the sensor and the viewfinder.) As all progress in quality seem to benefit both types of cameras, smartphone cameras will probably always remain the 'cheaper' one. 2003:F5:6F05:BC00:744A:96C9:C7E9:8B5 (talk) 22:07, 23 June 2020 (UTC) Marco PB[reply]
Is this why photos taken on smartphone cameras don’t have the same detail and depth as that taken on a DSLRs especially when photos are enlarged? Clover345 (talk) 22:23, 23 June 2020 (UTC)[reply]
Yes. A smaller sensor means either less or smaller pixels and less pixels means less resolution, smaller pixels means more sensitivity to noise. Less and smaller lenses means less luminosity and contrast. The link above explains all this and better. By the way there are so called Smartphone add-ons like this [[2]] Pictar Pro for $150 or several wide, makro, micro and tele lenses [[3]] or this Black Eye for $30 [[4]]. I find the idea ridicolous, because working with the same sensor you cannot get much better pictures than with the smartphone alone. And if somehow good photos matter to you, with the money you get a low end digital camera ways better than any smartphone, as Macon also says. 2003:F5:6F05:BC00:F1BF:F34C:1D5C:6819 (talk) 19:23, 24 June 2020 (UTC) Marco PB[reply]
Can they put a cylinder or cone frustum ridge on the back and fold the path to it with a 45 degree mirror? Someone must've patented the idea by now if it's not too simple. Sagittarian Milky Way (talk) 16:16, 24 June 2020 (UTC)[reply]
That only changes the shape of the space needed, not the amount of space needed. Unless someone comes up with some different physics than lenses and sensors, it will always be true that high quality photography requires a lens system with a large (compared to the space available in a smartphone) diameter and length.
The best practical advice is to get a low-end digital camera with a larger lens system and good reviews. For example the Canon PowerShot ELPH 190] costs $150 and takes far better pictures than any smartphone. --Guy Macon (talk) 16:28, 24 June 2020 (UTC)[reply]
I didn’t realise even point and shoots were better than smartphones. So what’s the main advantages of DSLRs or mirrorless cameras over point and shoots. Clover345 (talk) 20:51, 24 June 2020 (UTC)[reply]
Less diffraction and more light gathering capability with all its benefits, larger sensor, interchangeable lenses, more pixels, more features, better build quality, probably more that I don't know or remember now. Sagittarian Milky Way (talk) 01:39, 25 June 2020 (UTC)[reply]
I know about diffraction and shitty f/ratios, someone (not me) might be willing to have a clunky phone back to have a camera that's better than one only a few millimeters thick even though it isn't as wide, thick, bright or sharp as "real lens". Sagittarian Milky Way (talk) 18:48, 24 June 2020 (UTC)[reply]
If the image sensors of a camera can be manufactured to a much higher resolution (without losing much sensitivity), a compound eye as found in insects could serve as a model for a compound lens system whose separate images are fused (using quite some computing power) into a single image, thus creating a virtual lens with a much larger aperture. Compare the idea of very-long-baseline interferometry, in which fusion also achieves much higher resolution than any individual telescope is capable of.  --Lambiam 21:53, 24 June 2020 (UTC)[reply]
Smartphone cameras are heavily constrained by physics, but I would note there's an insane amount of money being spent on smartphone camera development, and phone processors are fast, allowing software tricks like analysing a picture, guessing what kind of photo you seem to be taking and adjusting the image to match. Although my iPhone's camera is nothing like as good as a DSLR, it is very good at getting the colour balance right. Blythwood (talk) 03:24, 29 June 2020 (UTC)[reply]

Antibodies for the present virus

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Is there any info regarding the structure of antibodies developed by recovered individuals exposed to the present virus?--109.166.135.226 (talk) 23:59, 23 June 2020 (UTC)[reply]

There is a race going on to find powerful antibodies that can be the basis of a COVID-19 vaccine or even a drug.[5][6][7] The urgency should be obvious for humanitarian reasons, but another powerful incentive is that the company that is the first to market will stand a good chance to make an ungodly profit, while latecomers may have wasted tremendous amounts of money – unless the earlier vaccine or drug is not very effective and theirs is much better. The profit motive is at the same time a strong reason not to share much information about what each company's scientists have been able to find out about the structure of antibodies that have been identified. So the published research, like this article, mainly comes from academia.  --Lambiam 13:23, 24 June 2020 (UTC)[reply]
See also Antibody#Structure.--Shantavira|feed me 16:53, 24 June 2020 (UTC)[reply]
I see there it says about the variable V region and the constant C region of the glycoprotein/antibody.--109.166.135.226 (talk) 13:25, 25 June 2020 (UTC)[reply]
It seems that some alternative variants to vaccins have been tried so far, like plasmapheresis. The use of alternatives generates some related questions re the identification of substructures of antibodies.--109.166.135.226 (talk) 13:41, 25 June 2020 (UTC)[reply]
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