Wikipedia:Reference desk/Archives/Science/2019 August 10

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August 10

Sourish smell of objects made of transparent glass

When you open an old cardboard-box full of objects made of transparent glass you shall notice a strange acidulous or sourish smell and also some sort of thin greasy film on these objects. The smell is very much like that of vinegar or old movie-reels in a humid environment. Now I would like to know how this greasy sourish film is created on the glass. Is it something from within the glass itself? Is there some chemical substance in the glass which could "eject" or "sweat" when the glass objects are kept away from fresh air? DannyJ.Caes (talk) 10:55, 10 August 2019 (UTC)

Cardboard would hardly be air tight and so chemical vapours will come and go from the box. Perhaps you are getting condensation on cool glass from hotter stuff in the air. If it is greasy, the chances are that it comes from cooking, especially frying in oil or fat. If you look here [1] you can see some chemicals found in unwashed clothes, butyric acid, Dimethyl disulfide, Dimethyl trisulfide, 2-heptanone, 2-nonanone, and 2-octanone. Perhaps you have some of these. The cardboard of the box could also give off smelly toluene, ethyl benzene, benzaldehyde, furfural, vanillin or 2-Ethylhexanol.[2] Graeme Bartlett (talk) 11:53, 10 August 2019 (UTC)

It doesn't come from the glass, it gets deposited on it. Unlike cardboard, it won't impregnate and will stay on the surface of the glass. Unlike plastic, glass is transparent and smooth, and have no smell of its own. Unlike metal, you won't mistake it for some sort of weathering/patina corrosion.

For all these reasons, you will easily notice a deposit you would miss or explain otherwise on another material. Gem fr (talk) 12:01, 10 August 2019 (UTC)

Strange as it is... it doesn't have to be a cardboard box, it could also be some corner in a closet or something. Fact is, the smelly objects made of transparent glass are always "forgotten" and "re-discovered" after several years of oblivion. The greasy feel and vinegar'esque odor is remarkable. DannyJ.Caes (talk) 12:33, 10 August 2019 (UTC)

Could you please give some examples of these 'objects made of transparent glass'? Thank you. 2003:F5:6F09:4700:11FF:191B:8EB6:2111 (talk) 17:28, 17 August 2019 (UTC) Marco Pagliero Berlin

Northern and southern crossings of the ecliptic and the galactic equator

The two crossings of the ecliptic and the galactic equator are located at the most northern and most southern locations of the ecliptic. Is this pure coincidence, or was there some sort of arrangement from the I.A.U. to shift the galactic equator a little bit to the point at exactly 90° of the ecliptic in Gemini, and at exactly 270° of the ecliptic in Sagittarius? On charts 136 and 339 in the Uranometria 2000.0 star atlas (1987 edition) I also see the crossing of R.A. 6 hours at the ecliptic's most northern location and R.A. 18 hours at the ecliptic's most southern location (Epoch 2000.0). DannyJ.Caes (talk) 11:33, 10 August 2019 (UTC)

Pure coincidence. Don't forget the ecliptic longitudes move backwards and go everywhere once every 26,000 years, or equivalently the stars and Milky Way move forward and leave their old coordinates behind. The second one's geocentric chauvinism of course, galaxies don't care about Earth. If I remember it crossed in 1998.Sagittarian Milky Way (talk) 14:26, 10 August 2019 (UTC)

You confused the precession of the Earth rotational axis with the precession of the ecliptic. Concerning the latter it does not change the arrangement between the ecliptic and galactic plane significantly as the Earth's orbital inclination is small. Ruslik_Zero 09:26, 11 August 2019 (UTC)

I know about precession of the ecliptic. The galactic equator obviously always crosses the ecliptic in Taurus or very close while the 90th degree of the ecliptic has to move. Sagittarian Milky Way (talk) 12:58, 11 August 2019 (UTC)

An entoptic phenomenon which looks like a small Circumzenithal arc

Here's something I discovered in 1978, age 14. I call it the Caes arc. It is only noticeable when one is looking at an angle of, say, 25 degrees away from a very bright white pointlike lightsource (dark background). The phenomenon looks like a small Circumzenithal arc with angular diameter of something like 5 or 6 Full Moons in a row. The colors of this arc are the "negative" of the commonly known spectrum. The convex side of this entoptic arc is aimed at the lightsource (just like the Circumzenithal arc). Around this arc there's a field-of-view filling cobweb of dark blood-vessels (the Purkyne tree). To get a perfect view of the entire entoptic phenomenon (the Caes arc and the field-of-view filling cobweb) one should try to "glide" the center of vision around the pointlike lightsource. Once you get the "trick" to perform this unusual technique, you shall be surprised! (so I was back in 1978 at age 14). And... no, I'm not a drugs-addict, and... yes, I am an optics-freak. Now, what I really want to know is, if my discovery of 1978 (the entoptic pseudo-Circumzenithal arc) was already known by someone else, say J.E.Purkyne, or not? Is it somewhere described in a scientific journal, such as the J.O.S.A. (Journal of the Optical Society of America)? Is it related to the entoptic phenomenae Haidinger's brush and Maxwell's Spot? DannyJ.Caes (talk) 11:47, 10 August 2019 (UTC)

Your description of Caes arc is not clear enough for me to understand what you mean. What the heck are you calling an angular diameter, and what is this "Full Moon" unit to measure it?

Entoptic_phenomenon#Examples has an image of Purkinje tree, an image of the retinal blood vessels in one's own eye, and a description of the procedure to see it, which seems to match what you do. Obviously known by Purkyne. But I guess you knew already

Gem fr (talk) 12:26, 10 August 2019 (UTC)

You are aware angular diameter is a perfectly fine and well known term, right? Fgf10 (talk) 12:36, 10 August 2019 (UTC)

The apparent diameter of this entoptic pseudo-Circumzenithal arc is something like five or six times the apparent diameter of the full moon (or the sun). Just like Haidinger's brush it is anchored at the center of the field of vision. In other words, one can't get rid of it once you know it's there, whenever you see a bright pointlike lightsource (dark background!). DannyJ.Caes (talk) 13:05, 10 August 2019 (UTC)

I wasn't. I am now, thanks Gem fr (talk) 19:56, 10 August 2019 (UTC)

"Halos" seems to be the term for this. It may be due to cataracts. Another term is halation (but not what our article talks about). Graeme Bartlett (talk) 13:11, 10 August 2019 (UTC)

M.G.J.Minnaert also mentioned these cataract-related "coronae" in his Light and Color in the Outdoors. You would think that Minnaert knew everything about optical phenomena in and outside the observing eye, but... he didn't knew about the entoptic pseudo-Circumzenithal arc. And... (by the way) he was not aware of the retro-reflective Cat's Eye effect in the human eye (only in the eyes of animals). DannyJ.Caes (talk) 13:32, 10 August 2019 (UTC)

What process of free radical substitution is affected when peroxidation within lipids has a temperature change? 42.2.149.179 (talk) 13:18, 10 August 2019 (UTC)

Reading different research papers and journals from various time periods, I see there is always mention that peroxidation of lipids is a result of free radical substitution, yet none of them can clarify whether it is in the initiation, propagation or termination stage. The dangers of ingesting peroxidated lipids are obvious but I wonder at what stage and how it becomes dangerous? 42.2.149.179 (talk) 13:18, 10 August 2019 (UTC)

See our lipid peroxidation article. DMacks (talk) 03:04, 11 August 2019 (UTC)

What is the furthest astronomical object who's motion on the celestial sphere has been detected?

Perpendicular to line-of-sight, not redshift or blueshift. I believe the tangential proper motion of the nearest non-dwarf galaxy has not been detected yet unless GAIA did it, thus it is not known if the blueshift means collision. I do not know if the nearer galaxies have been detected yet or anything in them or any globular clusters or the rotation of this galaxy. Sagittarian Milky Way (talk) 17:32, 10 August 2019 (UTC)

The proper motions of IC 10 and Messier 33 have been measured both with VLBI [3], Messier 31 and Messier 33 have also been done by GAIA [4]. But for the farthest, you ought to look at AGN jets, e.g. 3C 279 at redshift 0.54 [5]. --Wrongfilter (talk) 17:57, 10 August 2019 (UTC)

Edmond Halley noticed in 1750 that Sirius, Arcturus and Aldebaran, today known to be at 8.6, 36.7 and 65.3 Light-year distance respectively, were over half a degree away from the positions charted by Hipparchus roughly 1850 years earlier. DroneB (talk) 18:06, 10 August 2019 (UTC)

Taser electrocution

In some videos guys trying taser on themselves are held from both sides by two other guys. Why those two guys aren't electrocuted while touching the tasered guy? 212.180.235.46 (talk) 21:52, 10 August 2019 (UTC)

The electricity goes from one Taser connection to the other Taser connection, shortest path, so it won't go through someone touching the person getting Taser'd. RudolfRed (talk) 23:03, 10 August 2019 (UTC)

Or rather, most of it does. The flow of electricity will tend to spread out from a point and some will find other paths than the "shortest" one. This is one of the hazards of lightning, fallen power lines, and such. --76.69.116.4 (talk) 01:56, 11 August 2019 (UTC)

I wonder why the person collapses when hit by a taser, for example, on the shoulder. Could we assume that the electricity spreads through the whole nervous system? Is the pain unbearable? Shouldn't the current flow between the two electrodes mainly? --C est moi anton (talk) 17:26, 13 August 2019 (UTC)

There is only a tingling sensation as your muscle fibers between the electrodes contract. If you fight the taser, you recruit more fibers to contract, increasing tetany. If you ignore the feeling, you can keep fighting or running until the cops shoot you. Abductive (reasoning) 22:52, 13 August 2019 (UTC)