Wiki143:Reference desk/Science

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June 18

Health lore

Where does the advice to "keep your feet warm and your head cold" (widely believed in Eastern Europe) come from? Is there actual evidence of better health outcomes when following this advice? 2601:646:8082:BA0:196D:8E1:5181:D48F (talk) 02:08, 18 June 2025 (UTC)

Severe problems due to frozen toes (see Frostbite) or heat stroke are all too common. Of course, one's nose or ears can also be frostbitten, but this is far less common.  ​‑‑Lambiam 06:29, 18 June 2025 (UTC)

Might they be speaking metaphorically about the head, as in "keeping a cool head" when under stress? ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:06, 18 June 2025 (UTC)

Unlikely, given the grammatical construction of this sentence in languages other than English (in particular, in Russian it reads "keep your head in the cold" -- definitely referring to literal thermodynamics, not psychology). 2601:646:8082:BA0:D199:AB8A:25C3:B09B (talk) 23:54, 19 June 2025 (UTC)

Several sources attribute this advice to Herman Boerhaave (1668–1738): "Houd uw hoofd koel, uw voeten warm en prop niet te vol uw darm." ("Keep your head cool, your feet warm, and don't overstuff your bowels.") I have my doubts this is real; it sounds like a made-up attribution.  ​‑‑Lambiam 18:45, 18 June 2025 (UTC)

Thanks! And yes, it does actually sound completely plausible that he was the one who first published this advice -- given that the model of human anatomy he had come up with was essentially hydraulic in nature, it makes perfect sense that he would have believed that maintaining a temperature gradient between the head and the feet would improve circulation, whereas keeping the head excessively warm would hinder it! Now, for the second part of the question: does this actually result in better health outcomes, compared with keeping the whole body uniformly warm in cold temperatures or uniformly cool in hot temperatures? 2601:646:8082:BA0:D199:AB8A:25C3:B09B (talk) 23:54, 19 June 2025 (UTC)

Treatment

what is the function of lotion _Derma Dew? 223.185.220.224 (talk) 10:08, 18 June 2025 (UTC)

It is the brand name for a skin cream containing Aloe vera. That article describes its use. You'll also find it if you use a search engine for the brand. Mike Turnbull (talk) 11:02, 18 June 2025 (UTC)

June 19

Boiling point of nitrogen

Do we have a table for the boiling point of diatomic nitrogen as a function of pressure, especially between atmospheric pressure and its critical point? The infobox at the start of our Nitrogen article says that the critical point is near 3400 kPa and 126 K, but there's no reference given for that. I don't see data for pressures lower than that, other than a boiling point of 77 K at some unspecified pressure presumably near atmospheric. Ideally I'd also like a table of the liquid densities as a function of temperature in this range. I tried to look for other articles on en.Wikipedia, or phase diagrams on Commons, but all I found are two phase diagrams for much higher pressures. I don't need high precision data. Nitrogen is sold in pressurized cylinders for cheap so I expected this data to be widely available. – b_jonas 11:30, 19 June 2025 (UTC)

doi:10.5075/epfl-thesis-4721 has a nice phase diagram on page 61. It's cited to doi:10.1088/0031-9120/7/4/010, whose full-text I cannot access at the moment, so I don't know if it simply copied the diagram, used experimental or theoretical values from it, or has some other cited underlying source of information. DMacks (talk) 17:24, 19 June 2025 (UTC)

The labels have been reset in a serif typeface, but the grid and curves, although redrawn, are virtually indistinguishable.  ​‑‑Lambiam 20:36, 19 June 2025 (UTC)

Oceani (sic) Foam? 1960s Soviet breakthrough.

(Science seems to be the best here but this is more materials science or consumer science.)

On an episode of Gaslit about Nixon and Martha Mitchell, John Dean's character drops about how the Soviets invented a cushion foam that "feels better than you imagine". [1] (youtube link ap isn't working)

Is this real? How do you spell it? Any other info on this, like why after the cold war no one makes it?

Thanks in advance! 2600:1700:6742:3C00:C8E3:FC65:9FD0:D2C3 (talk) 18:07, 19 June 2025 (UTC)

Just tried looking it up under several different spellings, and the only refs I found led right back to the show -- so I can safely conclude that this material is purely fictional. BTW, the entire story is highly implausible on several counts: (1) having personally lived in the Soviet block during the last few years of the cold war, I can confirm that their foam cushions were not actually all that good -- they were very saggy and tended to support you in exactly the wrong places; (2) Kennedy would never have risked using Soviet-made materials in Air Force One (of all places) regardless of their supposed quality, for risk of public scandal; (3) I have found confirmation that the cushions on Air Force One were in fact manufactured in the USA (oh, the good old days!); and (4) the properties attributed to this "Poshinaya foam" appear to be similar to those of memory foam, which was invented during that time period (just about the only historically accurate part of this whole thing), but by Nasa, not the Soviets! 2601:646:8082:BA0:D199:AB8A:25C3:B09B (talk) 00:23, 20 June 2025 (UTC)

Really appreciate your deep dive on this. Hollywood always makes it look real smh. Any other thoughts or comments are welcome but what you are stating makes sense in some ways. 2600:1700:6742:3C00:C8E3:FC65:9FD0:D2C3 (talk) 03:11, 20 June 2025 (UTC)

Now that I remember this, there were even calls by local health experts to avoid using foam cushions in home furniture (and especially in children's furniture) because they believed them (and probably with very good reason) to contribute to poor posture due to their sagginess -- which shows just how bad Soviet-block foam cushions really were! 2601:646:8082:BA0:D83C:8BF:CC86:2F61 (talk) 12:05, 20 June 2025 (UTC)

Can you tell me something about two headed snakes?

As far as I know, two headed snakes are relatively common compared to other Siamese twins. Is it true that the two heads often get angry with each other and disagree about where their body is going and start fighting each other? 146.200.107.90 (talk) 22:47, 19 June 2025 (UTC)

The following article from a reputable source might be of interest; however, I didn't read it because I was required to "Enter your email to read this article", which I'm unwilling to do:

• --136.56.165.118 (talk) 00:42, 20 June 2025 (UTC)

Two quotes from that article:

Template:Tq

...

Template:Tq

There is no suggestion of anger being involved.  ​‑‑Lambiam 03:58, 20 June 2025 (UTC)

Unlike mammals, reptiles lay eggs, and the mother's body cannot detect and terminate severely deformed embryos early in development. Stanleykswong (talk) 20:18, 21 June 2025 (UTC)

Also, in placental mammals and many other viviparous animals, Siamese twins make delivery harder, endangering the mother. In humans it's almost certain to kill the mother without modern medical care. That increases the selection against genetic defects that cause Siamese twins. Some snakes employ some form of ovoviviparity. PiusImpavidus (talk) 09:03, 22 June 2025 (UTC)

Minor quibble: some species reptiles are viviparous (even some snakes). Two-headed snakes are probably rare enough that it would hard to look for a correlation with species. DMacks (talk) 12:01, 22 June 2025 (UTC)

June 21

Very small black holes

Black holes are right now thought to be characterized only by mass, angular momentum and charge. Could weak isospin also be a theoretical characterization? Aso I've heard that black holes could pass through us without our noticing. if they had angular momentum,charge, or hefty weak isospin, would they be more noticeable?Rich (talk) 20:55, 21 June 2025 (UTC)

Black holes vary in size, from tiny micro black holes to supermassive black holes that reside at the centers of galaxies. In theory, if the black hole is small enough, it is possible for a small black hole to pass through the Earth without us noticing. Although black holes have a high density, if the black hole is small enough, the effect of gravity on the tiny black hole will be negligible and we cannot detect it. Stanleykswong (talk) 11:33, 22 June 2025 (UTC)

It would be funny if it turned out that neutrinos are actually tiny black holes. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:03, 22 June 2025 (UTC)

It's not impossible. Neutrinos are extremely tiny particles, with a mass far lower than other elementary particles such as electrons. They have almost no size, so the density can be very high. In addition, they have no charge, so a large number of neutrinos can be concentrated in a very small space. Stanleykswong (talk) 16:13, 22 June 2025 (UTC)

Who told you that? --Wrongfilter (talk) 17:10, 22 June 2025 (UTC)

Neutrinos have a lepton number (unlike black holes, unless I'm mistaken) and obey the Pauli exclusion principle (so they can't be arbitrarily concentrated). AlmostReadytoFly (talk) 08:26, 23 June 2025 (UTC)

Note that micro black holes evaporate within a tiny fraction of a second -- and also note that, even for a Planck-mass black hole (10 micrograms), such near-instantaneous evaporation would release an energy of about 900 gigajoules (which, for comparison, is about the explosive power of a 500-lb high-explosive bomb like the ones we drop on Isis and other terrorist groups). So no, such a black hole still can't pass right through you for 2 different reasons -- (1) it will evaporate first, and (2) in doing so it would blow you to bits if it happened to be close enough! 2601:646:8082:BA0:BDCC:8484:2734:F138 (talk) 13:21, 22 June 2025 (UTC)

However, if such a hole were travelling close to the speed of light, relativistic time dilation would prolong its lifetime. See also Micro black hole#Expected observable effects. {The poster formerly known as 87.81.230.195} 94.6.41.216 (talk) 15:27, 22 June 2025 (UTC)

Still, assuming a casualty radius of 11 meters for the explosion caused by the evaporation of the black hole (implying blast effects only, no flying debris), the time dilation would have to be at least by a factor of thirty-six orders of magnitude to allow said black hole to pass through you and explode a safe distance away! (And if the explosion would create a significant amount of flying shrapnel, e.g. if it demolishes a parked car nearby, then that would add an extra order of magnitude for the time dilation required!) 2601:646:8082:BA0:F577:E853:35B:8DD9 (talk) 11:52, 23 June 2025 (UTC)

June 23

One minute earlier in 151 years

Accounting for DST today, the sun set on Sunday, October 4, 1874, in Oakland, California, at 6:47 PM. This year, in 2025, the sun will set at the same month, day, and location at 6:46 PM, one minute earlier in just 151 years. What factors account for this small difference? Viriditas (talk) 09:51, 23 June 2025 (UTC)

Milankovitch cycles? Although I suppose there might also be some rounding errors between whole minutes there? I guess we can rule out the unreliability of chronometers in Oakland in 1874? Martinevans123 (talk) 09:59, 23 June 2025 (UTC)

We have a good calendar that keeps calendar date in sync with the apparent motions of the sun. It ensures that on the same date the sun sets at the same time (with small variations). Or what did you actually expect? --Wrongfilter (talk) 10:08, 23 June 2025 (UTC)

• The solstice - the exact moment that the Earth's axis lines up with the sun - drifts around a little bit due to the fact that the year isn't a perfect 365 days. According to timeanddate.com, summer solstice 1874 was 21 June 15:07, and summer solstice 2025 was 21 June 02:42 UTC. That means that 4 October this year starts - in an astronomical sense, compared to the Earth's rotation around the sun - 12 hours earlier this year compared to 1874. Sunset times changes quite quickly in late September/early October (it looks like in Oakland, it's a minute or two per day), because it's near the equinox, and it's quite possible that that 12 hour difference is enough to push the sunset from one minute to another. In another year, when we have an unusually late solstice, October 4 will have a slightly later sunset, but most of us are unlikely to live to see it. The solstice date naturally gets slightly earlier every year by about 6 hours and 13 minutes, and that's why every 4 years we have a leap year - but the leap year correction still leaves about 13 minutes of drift per year. We try to cancel that out by skipping a leap year once a century (not counting years divisible by 400), so normally you get late solstices following a round century year (1800, 1900 etc) because the leap years are skipped in these years and that resets the calendar, but 2000 was a leap year so the calendar didn't get the usual reset. There won't be another late solstice until 2103, when it will occur at 22:47 UTC on 21 June - and that year Oakland will gain a minute and the sun will set at 6:48 PM (according to Wolfram Alpha). Smurrayinchester 10:35, 23 June 2025 (UTC)

  Thank you! Viriditas (talk) 10:59, 23 June 2025 (UTC)

  Many thanks, Smurrayinchester. Just for my info, are sunrise and sunset times always given in whole minutes? Martinevans123 (talk) 11:02, 23 June 2025 (UTC)

I think so. You can work it out more precisely, but the terminator (line of sunrise/sunset) moves at 463 metres per second at the equator, and slower the further towards the poles you go - you only need to walk a short distance to change the sunrise by a second. The sun rises and sets approximately 10 seconds earlier at the Tower of London compared to at Big Ben, for example, not taking into account all the other factors like the precise shape of the Earth and atmospheric effects that refract the sun's position. It's just not worth publishing sunrise times in seconds - it would be an example of false precision. Smurrayinchester 12:35, 23 June 2025 (UTC)

Many thanks for that very clear detail. Is that walking North or South, or East or West? Perhaps both. Obviously, in many places on land, the horizon will be obscured by terrain and/or structures. Is there an agreed official location for the sunset and sunrise in London? I would have guessed Royal Observatory, Greenwich. Sorry to keep asking! Martinevans123 (talk) 12:48, 23 June 2025 (UTC)

East-west. And I don't know if there's an official single point for astronomical calculations in London, but Greenwich certainly produce their own sunrise and sunset tables for astronomy. Smurrayinchester 15:01, 23 June 2025 (UTC)

The terminator moves across the Earth's surface with a speed of 360° of longitude in one day of 24 × 3600 s – not uniformly in October's Oakland, but the average is good enough here. The longitudinal width of Oakland is about 0.2°, so for the terminator to glide across Oakland takes about 48 seconds. Can we be certain that the reference point for 1874 is at the same longitude as that for 2025?  ​‑‑Lambiam 18:22, 23 June 2025 (UTC)

Yes, it's quite long, isn't it. Martinevans123 (talk) 18:30, 23 June 2025 (UTC)

There was no standard time in the United States in 1874 (History_of_time_in_the_United_States#Railway_time). So was 6:47 pm recorded in municipal time? Local solar time? Or something else? --Amble (talk) 22:05, 23 June 2025 (UTC)

(Just to be clear, I think the OP is talking about calculations of the kind you get from modern astronomical software, not measured local clock time. Even for precisely the same coordinates, the calculated sunset times vary for the reasons I listed above). Smurrayinchester 08:48, 24 June 2025 (UTC)

Your reply was fantastic, those effects can easily explain the variation. You are probably correct about the OP's data source as well. I initially thought it might relate to the long record of timekeeping data from Chabot Space and Science Center, which "served as the official timekeeping station for the entire Bay Area, measuring time with its transit telescope", but Chabot was only founded in 1883. --Amble (talk) 14:54, 24 June 2025 (UTC)

Smurrayinchester got this the wrong way round. It's easier to visualise using the autumnal equinox, which in 1874 fell on 23 September at 5:23 AM GMT and this year will fall at 6:19 PM GMT on 22 September. So this year 4 October falls 11h 4m further from the equinox than it did in 1874 and thus 11h 4m nearer to winter, meaning the sun sets earlier. The equation of time, which is partly affected by the time the apparent sun crosses the meridian, has little effect. In 1853, for example, this variable (which is subtracted from apparent (sundial) time to obtain mean (clock) time on 3, 4 and 5 October was respectively 11m 0.17s, 11m 18.33s and 11m 36.14s. You can check you are applying the equation correctly by considering the clock time at which the sundial shows noon: in early October the sundial is ahead of a clock set to local mean time (in practice standard (zone) time is used). With the cessation of direct astronomical observation from Greenwich parameters were recalculated using a zero meridian line a few yards from the one marked on the ground. 2A00:23C8:9626:8F01:F150:6B5A:4C04:3F82 (talk) 12:22, 25 June 2025 (UTC)

This implies that the October 4, 1874, sunset time for locations at Oakland's latitude should be equal, within a few seconds, to the mean of their sunset times for October 4, 2025 and October 5, 2025.  ​‑‑Lambiam 20:19, 25 June 2025 (UTC)

June 26

Butterfly watching question #2

I'm currently doing detailed planning for my trip to New England as mentioned 14 days ago (and will go on July 1), and I have some more specific questions to ask: I've found 2 other potentially promising locations for butterfly watching, one in Yarmouth, Maine and another in Waterville, Maine -- however, the question I will need answered before the end of this month is, in these 2 towns which species of tiger swallowtail is predominant, Papilio canadensis or P. glaucus (note no link to the article about the latter species)? 2601:646:8082:BA0:4C47:A4C8:EC7A:C5C6 (talk) 03:33, 26 June 2025 (UTC)

A quick Google finds:

Template:Xt [2]

Alansplodge (talk) 21:58, 27 June 2025 (UTC)

And distribution maps within Maine are here and here. Alansplodge (talk) 22:04, 27 June 2025 (UTC)

The scary butterflies are all confined to Hancock County! I hope somebody's told them that. Template:Tq - a possible reason for the distribution.  Card Zero  (talk) 22:12, 27 June 2025 (UTC)

Thanks! And I've actually been told by a local expert from Coastal Maine Botanical Gardens that P. glaucus is also predominant in Lincoln County, just to the west, and that the reason for this is the much milder winter due to the river nearby (and also that in recent years this species has been aggressively expanding its range northward, as is also the case with Papilio cresphontes) -- but he also told me that this far north, P. glaucus has a non-scary size (in fact, no bigger than P. canadensis), which makes it OK! (In fact, it's the P. cresphontes which is more likely to be a problem for me due to its size -- the expert told me that even in the Boothbay area, they can reach a size of 5-6 inches, although he might have meant (I hope) the ones in the butterfly house at the botanical garden, not the ones in the wild -- I guess I'll just have to see!) 2601:646:8082:BA0:D5E1:EC31:5434:1B47 (talk) 04:21, 28 June 2025 (UTC)

Carry a pair of strong nearsighted glasses; they make everything look smaller.  ​‑‑Lambiam 06:23, 28 June 2025 (UTC)

Hahaha, I actually don't think I'll need to bother -- this source says the P. cresphontes in Canada have a size range of 3 1/4 to 4 1/2 inches (the two pinned specimens at the Royal Ontario Museum in Toronto had a wingspan of only about 3 inches or so, I measured with my finger against the glass), and since Maine is not any farther from the northern edge of their range than Toronto (or even Ottawa), they should be no bigger than that up there either -- which, for a non-tiger-striped species like this one, is perfectly fine by me! (That guy must have been talking about the ones in the butterfly house, not those in the wild!) And if I do see a giant swallowtail which is too giant for me, I expect I'll be able to see it from afar and make myself scarce before it gets too close -- but I don't expect this will happen! 2601:646:8082:BA0:B4C5:E96C:7826:47EE (talk) 13:45, 28 June 2025 (UTC)

We can't wait to hear your trip report once you made it (hopefully safely) back.  ​‑‑Lambiam 05:22, 29 June 2025 (UTC)

Not to worry, will do! And seriously -- barring some freak accident as a result of a panic attack (a vanishingly small possibility, as even having a panic attack in the first place would require some improbable turn of events, for the reasons I've stated above, and even if it happens it's unlikely to lead to anything worse), the worst that can happen is that instead of being desensitized I'd end up traumatized worse than before -- but even that is highly unlikely, given how gradually I'm doing this (hence my choice of location, selected specifically so that I have a good chance to see P. canadensis and not run into its bigger cousins like P. glaucus) and how much progress I've already made in the past 7 years! Of course, with an animal phobia, going from pictures and figurines to real live animals is always a big step (because a real live animal has a mind of its own, so you don't have any control over what it does) -- but I've made every effort to make this step go as smoothly as it possibly could! 2601:646:8082:BA0:E08A:96DE:28D8:2E6F (talk) 02:22, 30 June 2025 (UTC)

June 29

The list of all the reproaches against cryonics

Hello, I apologize for the inconvenience, but I'd like to know the list of things that the scientific community criticizes about current cryonics, please. I know that there's the excessive deterioration of neurons, the failure to preserve the excitability threshold of synapses; moreover, there's a hypothesis according to which a certain structure of molecules inside synapses must also be preserved (as we're not sure that this hypothesis is false, we'll have to converse with it as a precaution) ; and else...? 78.240.199.90 (talk) 16:01, 29 June 2025 (UTC)

IP editor: The section at Cryonics#Obstacles to success has quite a lot of criticisms. Other contributors here may suggest more. Mike Turnbull (talk) 16:58, 29 June 2025 (UTC)

If the business is not strongly regulated, with good oversight, any bunch of con artists can start a cryonics firm, swearing by all that is holy that they are industriously and meticulously applying best practice using the most advanced science and technology this side of the Milky Way, while not doing much more than keeping up an impressive Potemkin village.  ​‑‑Lambiam 17:41, 29 June 2025 (UTC)

• There is no inconvenience, OP. We invite questions such as yours. Rest easy. -- Jack of Oz ^{[pleasantries]} 21:40, 29 June 2025 (UTC)