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March 22

Isp calculations

I've been working on a tool to calculate delta-v, and I got a little stuck. Specifically, how do you calculate specific impulse of a rocket when you have multiple engines with different specific impulse and thrust firing at the same time (example: 4x RS-25 + 2 SRBs)? Assume constant thrust, no atmosphere, no gravity. Stoplookin9 Hey there! Send me a message! 02:13, 22 March 2025 (UTC)

The acceleration of the rocket equals its mass divided by the thrust. The combined thrust is constant (assuming no engine runs out of fuel); it equals the sum of the thrusts of all engines. Let $T_{\mathsf {E}}$ denote the thrust of engine E. The total thrust is then given by the sum of all individual thrusts: $T=T_{1}+T_{2}+...\,.$ The difficulty of the problem is that the acceleration is not constant. The mass decreases as rocket fuel is consumed, which means that the acceleration increases. To solve this requires to use some integral calculus. We need to know the total mass of the system at the start; let's call it $M$. How does it decrease as fuel is burned? Let $I_{\mathsf {E}}$ denote the the specific impulse of engine E. The contribution of this engine to the rate of fuel mass consumption equals $Q_{\mathsf {E}}=T_{\mathsf {E}}/I_{\mathsf {E}}.$ Sum this quantity over all engines to get the total mass flow rate $Q=Q_{1}+Q_{2}+...$. After a time $t$ has elapsed, the mass of the whole system will have decreased to $M-Qt.$ So the acceleration at time $t$ after the start equals $T/(M-Qt).$ To get $\Delta v$ after a burn time $\Delta t$ we need to integrate this:

$\Delta v=\int _{0}^{\Delta t}{\frac {T}{M-Qt}}\,{\text{d}}t={\frac {T}{Q}}\log \left({\frac {M}{M-Q\Delta t}}\right).$

The $\log$ function in this formula is the natural logarithm, so, for example, $\log(1.35)\approx 0.30\,.$  ​‑‑Lambiam 11:49, 22 March 2025 (UTC)

Specific pulse is the ration of the trust to the mass flow of the propellant. You can do the simple calculation knowing thrusts and specific pulses of all engines. Ruslik_Zero 20:02, 22 March 2025 (UTC)

This only works if the mass of the fuel consumed during the burn ($Q\Delta t$ in the formula above) is insignificant, compared to the total mass. Writing $q={\frac {Q\Delta t}{M}},$ we can expand ${\frac {M}{T}}{\frac {\Delta v}{\Delta t}}$ as a Taylor series:

${\frac {M}{T}}{\frac {\Delta v}{\Delta t}}=1+{\frac {q}{2}}+{\frac {q^{2}}{3}}+\cdots \;.$

 ​‑‑Lambiam 07:48, 23 March 2025 (UTC)

It will work in any case:

$sfc={\frac {\sum thrust_{i}}{\sum {\frac {thrust_{i}}{sfc_{i}}}}}$.

All these engine parameters (thrusts and specific fuel consumptions) are just constants. Ruslik_Zero 19:05, 23 March 2025 (UTC)

Actually in your formula $T/Q=sfc$. Ruslik_Zero 19:10, 23 March 2025 (UTC)

How do you get from ${\mathit {sfc}}\,$ to $\Delta v$?  ​‑‑Lambiam 09:19, 24 March 2025 (UTC)

By tsiolkovsky rocket equation as usual. Ruslik_Zero 19:52, 24 March 2025 (UTC)

Tsiolkovsky's formula is the answer I gave; $M-Q\Delta t$ is the remaining mass after a burn time $\Delta t.$ Tsiolkovsky's formula assumes that all fuel is consumed. In the case of multiple engines with different characteristics, I don't think we can assume all burn out at the same time, and then the formula no longer works. You need to calculate $\Delta v$ to the first burn-out, then add the $\Delta v$ from that point till the next burn-out, and so on.  ​‑‑Lambiam 23:23, 24 March 2025 (UTC)

What is the correct name for prompts used for AI generation

Is it AI-generation prompt or AI-generated prompt Trade (talk) 11:43, 22 March 2025 (UTC)

Neither of the two sounds natural to me. If it is clear that the context is generative AI, just "prompt" will generally do just fine. If, in the context, you need some attribute to distinguish it from other kinds of prompts, you can use "GenAI prompt"^[1] (or possibly, depending on the audience, the longer term "generative-AI prompt").  ​‑‑Lambiam 12:00, 22 March 2025 (UTC)

"AI-generated prompt" is the least correct of the options the OP and Lambiam have proposed. It means that the prompt is generated by AI, not that the prompt is used to have AI generate something. DMacks (talk) 12:18, 22 March 2025 (UTC)

"AI prompt" is used in documentation for ChatGPT, DeepSeek, and DALL-E. The word "generative" has special meaning in AI. You can't just toss it around willy-nilly. 12.116.29.106 (talk) 17:34, 25 March 2025 (UTC)

March 23

Metrication

Is there any Anglophone country that was fully metric in 1950? --40bus (talk) 23:34, 23 March 2025 (UTC)

Reviewing the Metrication article, the answer would seem to be "No." ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:18, 24 March 2025 (UTC)

If many Spanish colonies in the Americas metricated in 19th century, why didn't British colonies do same? Why did Australia only metricate in 1970s? --40bus (talk) 06:55, 24 March 2025 (UTC)

Anglophone colonies (to make a sweeping generalisation) took their lead from the UK which had little interest in metrification back then; there was simply no pressing reason for it*, and since it was perceived as a French idea, there would have been active cultural hostility towards its adoption. France adopted it in the wake of a huge politico-cultural revolution; the Anglosphere had no such cusp to prompt an abandonment of comfortably familiar tradition.

(* Of course, it was useful scientifically, but Anglospherical (!) scientists were quite happy to use metric units in the lab and imperial ones in their daily lives. This was still the case when I was schooled, and in the UK is still true to a certain degree today.) {The poster formerly known as as 97.81.230.195} 94.2.64.108 (talk) 11:00, 24 March 2025 (UTC)

I'm not sure what 'fully metric' means precisely, but are there any Anglophone countries that are 'fully metric' in 2025? Sean.hoyland (talk) 08:00, 24 March 2025 (UTC)

Australia did a fairly thorough job with its conversion. But US dominance gets in the way of perfection. We have Subway, with its foot longs. I saw a debate today as to whether tyre pressures should be in Kilopascals, or PSI. And of course, aviation measurements are imperial. HiLo48 (talk) 08:29, 24 March 2025 (UTC)

In Finland, Subway sandwiches are sold in sizes of 15 cm and 30 cm. These numbers are highly divisible numbers that divide evenly by 3 and 6 (15⁄6 is still terminating [2.5]). These sandwiches can be cut equally into3 and 6 pieces. Rulers are also 30 cm long. Are there any English-speaking countries where sandwiches are sold in 15 cm and 30 cm sizes? --40bus (talk) 21:23, 24 March 2025 (UTC)

Sandwiches typically don't have a constant cross-section, so if you cut them in pieces of equal length, you don't cut them in pieces of equal mass. Anyway, how often have you seen somebody cut a sandwich using a ruler? PiusImpavidus (talk) 10:50, 25 March 2025 (UTC)

40bus 12 inches is divisible by 1, 2, 3 (giving 3 1 hand sandwiches), 4, 6 and 12. Dividing by 5, 8, and 10 is terminating, dividing by 9 is exactly 1 inch 1 barleycorn. Dividing by 36 is one barleycorn. Dividing by 144 is one line. Dividing by 1728 is one hair. So 1 foot is divisible by 1, 2, 3, 4, 6, 8, 9, 12, 16, 18, 24, 27, 32, 36, 48, 54, 64, 72, 96, 108, 144, 192, 216, 288, 432, 576, 864, and 1728. 12 and 6 inch sandwiches can be cut into 1, 2, 3 and 6 pieces in whole inches. Rulers are also 12 inches or 6 inches long. A foot is also about a foot long, meaning you can keep these rolls in your shoe. All the best: Rich Farmbrough 22:53, 25 March 2025 (UTC).

HiLo48, I've not eaten Subway very often since immigrating (I've not been able to get work comparable to what I had in the US), but on the occasions when my family and I have gone to Subway here, I've always been amused by the fact that Subway Australia has a trademark on "six-inch" and "foot-long" :-) So it's not exactly a measurement but a distinctive name for specific sandwiches. Nyttend (talk) 20:59, 28 March 2025 (UTC)

40bus — Subway and aviation aside, Australia has occasional pre-metric measurements. You'll see inches used at JB Hi-Fi for TV screens, at Supercheap Auto for windscreen wipers, and at Bunnings for nails. Nyttend (talk) 21:04, 28 March 2025 (UTC)

The sticker in the door of my mother's car has both kPa and PSI. Most people I know use PSI - pressure is hard to visualise and to most the tyre pressure is just a number. We still have pints in the pub, which in South Australia is 425ml, but 570ml in the other states. If you want to replace a door in a house, you buy a 900mm door, which I suppose is metric, but really it's 3 feet. TrogWoolley (talk) 10:32, 24 March 2025 (UTC)

The answer, as always to the OP's "why don't..." questions is that "They didn't want to". The Metrication Board was disbanded, the reason being that people didn't see why they should be fined for buying and weighing out potatoes in pounds and ounces. Traders can still be fined for weighing them out in Imperial, but that's as far as it goes. My good friend Colin Hunt was targeted by weights and measures inspectors, who pounced when he made an arithmetical mistake in a conversion. His sister Janet also suffered. I was in Australia in 1971 when people still referred to the 20 cents coin as "two bob". I am intrigued as to why the South Australian pint is 425 millilitres. Here it's 568 millilitres. West Australian publicans would never treat their customers like that. According to our article, the U S pint is 473 millilitres. 2A00:23C5:8410:4A01:907A:4B08:B028:3AA1 (talk) 12:54, 24 March 2025 (UTC)

40bus keeps having trouble understanding that different countries (or cultures or languages or ...) are different. It comes across as exceptionally arrogant to expect everyone, everywhere, to do everything exactly the way he (?) is used to in Finland. --User:Khajidha (talk) (contributions) 12:10, 26 March 2025 (UTC)

In fairness, he (?) actually is doing better in this thread, as many of the questions are phrased "are there any..." and such as opposed to "why did"/"why didn't". --User:Khajidha (talk) (contributions) 12:15, 26 March 2025 (UTC)

My brother has just become a grandfather for the 7th time. The email announcement told us the child weighed so many pounds and ounces, not kilograms. That tradition doesn't look like going away any time soon. -- Jack of Oz ^{[pleasantries]} 20:35, 24 March 2025 (UTC)

JackofOz, interesting. Both of our children were born after we immigrated, and the hospital told us only kg and cm, not pounds-and-ounces or feet-and-inches. Do many people really take the hospital-provided data and convert before sending out birth announcements? Nyttend (talk) 19:24, 30 March 2025 (UTC)

I don't know what sort of info hospitals give out these days, Nyttend. But I've seen all manner of birth announcements - from family and friends, to notices in shop windows for a mother who works there - and it's still always in lbs and ozs (sometimes with the metric equivalent added, but mostly not). Very few women giving birth now were born before metrication, and they've been buying grocery and supermarket items in kilos all their lives, but that doesn't cut any ice when it comes to birth announcements, apparently. Sp I'd never be surprised if hospitals routinely do the conversion because they know the mothers are going to ask for it. -- Jack of Oz ^{[pleasantries]} 22:31, 30 March 2025 (UTC)

It makes sense to use metrics within science, and it also makes sense to use human measurements in other contexts. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:08, 24 March 2025 (UTC)

What are "human measurements"? -- Jack of Oz ^{[pleasantries]} 06:07, 25 March 2025 (UTC)

Inches, feet, and the like. A meter comes fairly close to being a natural measurement, being just a bit longer than a yard. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:29, 25 March 2025 (UTC)

Protagoras c. 490 BC – c. 420 BC may have meant that "Of all things the measure is Man ('s foot ?)." Philvoids (talk) 08:59, 25 March 2025 (UTC)

A centimetre comes close to the width of my little finger ("pinky" for you), while the mile is an inhuman measurement.  ​‑‑Lambiam 13:03, 25 March 2025 (UTC)

Mile is derived from Latin, mille, thousand, referring to 1,000 paces of a human adult. -- Jack of Oz ^{[pleasantries]} 20:42, 25 March 2025 (UTC)

That's a double pace (passus), see Ancient Roman units of measurement#Length, equal to five roman feet. Mikenorton (talk) 23:23, 25 March 2025 (UTC)

That probably accounts for why the statute mile is in the neighborhood of 5,000 feet. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:41, 26 March 2025 (UTC)

In the UK, "foot-long subs" are advertised and presumably a standard, but since 1 foot exactly is 30.48 centimetres (and if you're rounding to the nearest inch can be 29.21–31.75 cm), and since bread products inherently vary in their exact dimensions, 1 ft and 30 cm are effectively the same.

School (etc.) rulers in the UK have customarily been marked in inches on one edge and centimetres on the other for at least 60 years to my personal observation. {The poster formerly known as 87.81.230.195} 94.2.64.108 (talk) 02:45, 25 March 2025 (UTC)

In Perth in 1971 residents were enjoying WA's first Kentucky Fried Chicken, which had just opened on the corner of Canning Highway and Stock Road. I would imagine that the presence of multinationals would put a damper on full metrication (as HiLo48 noted). I was surprised to learn that people put a ruler up against sandwiches to classify them. I've only seen them in standard-size packs which itemise the ingredients but don't say how big they are (in the manufacture of the raw material, bakers distinguish between "thin", "medium" and "thick"). 80.43.76.22 (talk) 12:00, 25 March 2025 (UTC)

One point of interest - in Australia mileages (do they still call them "mileages"?) are metric. Do people still use miles? Do rulers still carry inches? What exactly have been the metric inroads to life there in the last half century? 80.43.76.22 (talk) 12:10, 25 March 2025 (UTC)

Nominally only a few items remain Imperial in formal British life, some measurements relating to road use, the pint for draught beer and cider, champagne and reusable milk bottles (pinta), the troy ounce for precious metals. Aircraft altitude is I believe still measured in feet, worldwide. All the best: Rich Farmbrough 23:08, 25 March 2025 (UTC).

And railways of course, with the exception of HS1. Shantavira|^{feed me} 09:38, 26 March 2025 (UTC)

Another target is temperature. On a warm spring day do Australians say it is "in the seventies" or "in the twenties"? 80.43.76.22 (talk) 15:12, 26 March 2025 (UTC)

The latter. Since immigrating here from the US, I've never encountered Fahrenheit, except (1) when talking with American relatives and friends, and (2) on the occasional news segment that features Americans talking about the weather. Nyttend (talk) 19:23, 30 March 2025 (UTC)

Aircraft altitude is a strange case: it used to be metric in most of the world (most of the non-anglophone world anyway) and switched after World War 2 under the influence of British and American aircraft builders. Similarly, aircraft speeds switched from km/h to knots. A rare case of demetrication. PiusImpavidus (talk) 18:34, 26 March 2025 (UTC)

Prior to WWII, which countries manufactured most of the airplanes? ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:15, 26 March 2025 (UTC)

I suspect that prior to WWII, most aircraft-operating countries manufactured their own aircraft. {The poster formerly known as 87.81.230.195} 94.2.64.108 (talk) 03:52, 27 March 2025 (UTC)

Most of the large and many of the medium sized countries in Europe had a sizeable aircraft industry; in particular Germany and France. The war turned out to be bad for the aircraft industry on the loosing side and good on the winning side, where being occupied by Germany put you on the loosing side. Eventually the European aircraft industry recovered, but that was when the switch to feet had already happened (except in the Soviet Union, but they didn't sell so much to western countries). PiusImpavidus (talk) 11:38, 27 March 2025 (UTC)

Some years ago, I worked at the UK Met Office. We used a very strange mix of units there, largely influenced by aviation usage. Altitude in feet (unless you were dealing with things in the upper atmosphere, in which case we would use kilometres); distance in metres when talking about visibility, but nautical miles for distances between locations; speed in knots; temperature in C; pressure in hPa. This was over 20 years ago - I don't know if that is still the standard. Iapetus (talk) 13:01, 27 March 2025 (UTC)

March 27

Employment rates among schizophrenics

From the Vermont longitudinal study:

Twenty-six percent (N=44) of the 168 subjects were employed; half of them were classified as working in unskilled jobs. Thirty-three percent (N=56) were un-employed, 8% (N= 14) were volunteers, and 5% (N=8) were housewives. Due to the advanced ages in the sample, an additional 26% (N=44) were classified as elderly, widowed, or retired. Solid information was unavailable on four (2%) of the subjects for this rating.

Is it just me or does her math not add up? If you have 168 subjects, and 44 employed, 56 unemployed, 14 volunteers, 8 housewives, 44 EWR, 4 not assessed, you get 170? Aside from this, does this mean of the 168 diagnosed with schizophrenia who were work eligible (116, 168 minus 8 housewives minus 44 elderly, widowed or retired), a full 37% were employed? This would seem to conflate with the 10% general employment rate for schizophrenics? I'm aware of the law of small numbers as described in Thinking Fast and Slow leading to more lopsided results, would this be an example of that? The study's author just published a book through Oxford University press, is this a scam or is it a worthwhile read? Therapyisgood (talk) 03:26, 27 March 2025 (UTC)

The Oxford University Press is about as respectable a publisher as one could hope to find – it's unlikely that they would publish a 'scam'.

The apparently error-containing paper you have quoted and linked appeared in a journal in 1987; I think it unlikely that one minor mistake in a research paper co-authored 37 years ago by 5 people (only one of whom is the author of the new work) has much bearing on the quality of a book published only last year.

Few if any works, even scholarly ones, are entirely without errors whether by the author or the typesetters; this is especially true of matter published in journals with their frequent and pressurised deadlines, as opposed to books which have a more protracted editorial process. I am a former editor (who once turned down a job offer from OUP because of travel logistics!), and rarely see any book or periodical without at least one typo. (A pro or ex-pro editor notices such things when reading even when not looking for them.)

I don't know the source of this error, if it is one, but I doubt it casts significant doubt on this researcher's competence. Have you checked subsequent issues of the journal to see if it published a corrective note? {The poster formerly known as 87.81.230.195} 94.2.64.108 (talk) 04:19, 27 March 2025 (UTC)

The easiest explanation is that a clerical error was made in the last sentence, which should have read, "Solid information was unavailable on two (1%) of the subjects for this rating."  ​‑‑Lambiam 13:41, 27 March 2025 (UTC)

Have you considered the possibility that one of the housewives -- or the employed, or unemployed -- volunteers? Some people might fall into more than one category. DOR (ex-HK) (talk) 22:04, 4 April 2025 (UTC)

Can "Chemical castration" be reversal like "Vasectomy reversal"?

Can "Chemical castration" be reversal like "Vasectomy reversal"?

I didn't find any information about that. HarryOrange (talk) 06:19, 27 March 2025 (UTC)

Yes, usually. The second paragraph of the Wikipedia article covers this, and references are widely available online. Larry Hockett (Talk) 06:50, 27 March 2025 (UTC)

Gas carbon

What is "gas carbon", as referred to in "plates of gas carbon" and "a cylindrical piece of gas carbon", in "The Microphone, Magnophone, Phonoscope, and Phoneidoscope"? (It's not an easy term to Google, due to false positive results.) Andy Mabbett (Pigsonthewing); Talk to Andy; Andy's edits 13:49, 27 March 2025 (UTC)

Seems to be a type of soot used to make early carbon microphones. Charcoal seems to have been used later. Mike Turnbull (talk) 14:30, 27 March 2025 (UTC)

Thank you. I now see that we used to have a stub at [2], but User:Materialscientist redirected it last year, to Carbon, apparently without there being anything on the subject at the target. Perhaps it should be resurrected? Or the content included somewhere? It was clearly a significant material at some time ([3], [4], [5]). Andy Mabbett (Pigsonthewing); Talk to Andy; Andy's edits 15:01, 27 March 2025 (UTC)

Here are some book sources: [6], [7], [8], [9], [10], [11], [12]. There is a text on Wikisource, Popular Science Monthly/Volume 7/July 1875/Notes, where it is called "gas-retort carbon".  ​‑‑Lambiam 10:40, 28 March 2025 (UTC)

Thank you. I have also seen it called "retort carbon". Andy Mabbett (Pigsonthewing); Talk to Andy; Andy's edits 11:35, 28 March 2025 (UTC)

That name is also used by the third source in the list above, as well as the amusing variant "retort-scurf ".  ​‑‑Lambiam 21:34, 28 March 2025 (UTC)

I have restored Gas carbon, and expanded it. There is also an ongoing discussion of whether to mention it in Carbon microphone, on the latter's talk page. Andy Mabbett (Pigsonthewing); Talk to Andy; Andy's edits 16:26, 29 March 2025 (UTC)

• It's soot. But the point is that it's a solid carbon deposited by a vapour phase process (see chemical vapor deposition, although this isn't epitaxial). That gives it a particular mechanical structure. In this case one with a surface that produces grains which, when loosely packed, gives a surface contact and resistive connection that's extremely variable, and varies by mechanical contact pressure. So for the carbon microphone, one where there's a correlation between the physical movement (caused by the microphone diaphragm) and the electrical resistance of the microphone, thus the output signal. Andy Dingley (talk) 00:04, 30 March 2025 (UTC)

March 28

Russian sleep

I recall reading, decades ago, of a development by Soviet scientists of a technique for inducing sleep via electric current applied to, I think, the eyelids. It's used as a plot element in certain Larry Niven stories, especially A Gift from Earth. But I haven't had much luck googling it; it's confounded by a grossout story called the "Russian sleep experiment", and if I add -experiment to the search, I get a lot of random stuff but not what I'm looking for.

Do we have an article covering this? --Trovatore (talk) 07:15, 28 March 2025 (UTC)

Apparently, it's a deep state rabbit hole and Google's AI gives an overview regarding "electrosleep Pavlov".[13] Modocc (talk) 14:13, 28 March 2025 (UTC)

See also Cranial electrotherapy stimulation: "CES was initially studied for insomnia and called electrosleep therapy." Modocc (talk) 14:26, 28 March 2025 (UTC)

Thanks, Modocc. That does look like what I was looking for. I still find it a little surprising that there isn't more on this. Insomnia is a huge medical issue that could attract massive money, and this is such a simple thing. You'd expect to see, if not more use of it, then some sort of reason why, along the lines of "we couldn't reproduce the Soviet results" or "well, it sorta works sometimes but not really that well" or "it has these significant downsides", but mostly it seems to be just kinda half-ignored. --Trovatore (talk) 23:52, 28 March 2025 (UTC)

I read somewhere that Niven said it doesn't work, much to his disappointment. Abductive (reasoning) 19:16, 30 March 2025 (UTC)

March 30

Proximity of eclipses, in time

We had a solar eclipse yesterday, 29 March, 15 days after a lunar eclipse on 14 March.

Is it common to have the two types of eclipse so close together? What is the closest in time that they have or are likely to occur? Andy Mabbett (Pigsonthewing); Talk to Andy; Andy's edits 14:57, 30 March 2025 (UTC)

In general, solar and lunar eclipses often come in "pairs". This page has the pairings for the current year.[14] ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:55, 30 March 2025 (UTC)

Since one happens at a full moon and one happens at a new moon, the closest they can come is 14-15 days. Floquenbeam (talk) 18:01, 30 March 2025 (UTC)

Yes. I could imagine that the exact number of days, hours and minutes between each could vary somewhat. It could be interesting to review a few of them and see how much time there is between the points of totality or the closest thing to it, for a few recent and future years, and see how much variance there is. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:06, 30 March 2025 (UTC)

Half a month apart is the closest they can occur. A solar eclipse happens when it's new moon and the line of nodes of the moon's orbit points more or less to the Sun, a lunar eclipse when it's full moon and the line of nodes points more or less to the Sun. Over two weeks, the Earth doesn't orbit too far around the Sun, so the line of nodes (which only changes slowly) still points more or less right. These eclipses often come in pairs, although on many occasions (including this one), at least one of them will only be a partial eclipse. About half a year later, the line of nodes points again more or less right, giving two more opportunities. PiusImpavidus (talk) 18:10, 30 March 2025 (UTC)

(ec, not much difference to PiusImpavidus' reply) An eclipse happens when full or new moon occurs at one of the lunar nodes, i.e. the intersections of the moon's orbit and the ecliptic. Because earth and moon run around the sun, the syzygies shift with respect to the node passages. However, this shift is slow enough that half a synodic month after an eclipse the moon can again be sufficiently close to a node that another eclipse can occur; therefore pairs of eclipses are fairly common. The time between two node passages is a draconic month (27d 5h 5m), the time between two full moons a synodic month (29d 12h 44m). --Wrongfilter (talk) 18:20, 30 March 2025 (UTC)

This led me to this unanswered question from Baseball Bugs: Wikipedia:Reference desk/Archives/Science/2014 December 25#Christmas Day moon eclipse. There are two tropes that are repeated over and over again by people who have an agenda. The first is that a canon of the Council of Nicaea ordained that Easter must be celebrated in the week following the full moon which occurs on or next after 21 March. It didn't. Reads the canons. The second is that some Orthodox churches observe the dedicated festival of the Nativity in January. Nobody observes it in January. Orthodox churches which use the Revised Julian calendar celebrate it on the same day as us, 25 December. Orthodox churches which still use the Julian calendar likewise celebrate it on 25 December, which for the time being falls on the same day as our 7 January. 2A00:23C7:C9B7:A01:68B1:562A:5DCE:A157 (talk) 09:55, 31 March 2025 (UTC)

There's always at least 2 eclipses per eclipse season. But never more than 3. Most commonly 2. A Gregorian year Anno Domini can have 4 to 7 inclusive. Sagittarian Milky Way (talk) 04:50, 4 April 2025 (UTC)

March 31

End of the worl [sic]

is the worl going to end? 41.122.78.118 (talk) 14:59, 31 March 2025 (UTC)

Eventually. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:34, 31 March 2025 (UTC)

Solipsistically, après moi, le déluge. See also Global catastrophe scenarios. {The poster formerly known as 87.81.230.195} 94.2.64.108 (talk) 15:45, 31 March 2025 (UTC)

To a true solipsist, there is no such thing as après moi.  ​‑‑Lambiam 23:06, 31 March 2025 (UTC)

The world, not anytime soon. The US, ¯\_(ツ)_/¯. Clarityfiend (talk) 15:50, 31 March 2025 (UTC)

Shortly before d time. DuncanHill (talk) 20:04, 31 March 2025 (UTC)

Define world. Define end. --User:Khajidha (talk) (contributions) 21:23, 31 March 2025 (UTC)

You misspelled "worl". The correct spelling is "whorl". If the whorl is an ideal mathematical logarithmic spiral, it extends infinitely, both outwards and inwards, but the whorlings of any material realizations eventually come to an end, either because they reach an end of the material of which the whorl is fashioned, or because its very whorliness ceases to whorl. Or, after a very long time, the whorl itself may cease to exist as such; see Ultimate fate of the universe.  ​‑‑Lambiam 23:04, 31 March 2025 (UTC)

If ". . . worl [sic]" indicates intentional spelling, then worl might be the Jamaican patois rendering of 'world', in which case Rastafarian millenarianism may apply – see Rastafari#Salvation and paradise. {The poster formerly known as 87.81.230.195} 94.2.64.108 (talk) 06:42, 1 April 2025 (UTC)

Idicates? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:21, 1 April 2025 (UTC)

Thanks, corrected. My keyboard has recently become recalcitrant. {The poster formerly known as 87.81.230.195} 94.2.64.108 (talk) 13:54, 1 April 2025 (UTC)

This [sic]-ness was not added by the OP, who presumably was seeking a science-based answer.  ​‑‑Lambiam 11:50, 1 April 2025 (UTC)

I cannot tell a lie. It was I, m'lud. But I don't resile from it. The original header was "Science", which is exquisitely unhelpful for a header on a page where every thread, ever, is by definition about science. So I borrowed the OP's own words, but I thought it would be presumptuous to translate their spelling into what I guessed they were probably asking, so I left them exactly as written, but I wasn't going to have my legacy to posterity be that my unprecedented spelling error was on a Wikipedia page, so I did what any gentleman would do: I noted the placement of the gun on the sideboard, considered my position, and did the decent thing. -- Jack of Oz ^{[pleasantries]} 18:16, 1 April 2025 (UTC)

The world ends each instant of time. See also here. Count Iblis (talk) 09:59, 1 April 2025 (UTC)

While a claim posted on April Fools' Day must encounter a well founded tradition of scepticism about its seriousness, the evidence on April 2nd is that what you posted has survived in legible form through a day's rotation of our planet, is likely to continue do so, and thereby establishes that the world in which you wrote did not end entirely immediately after you wrote. The monistic assertion that there exists only a single thing, the universe, which can only be artificially and arbitrarily divided contradicts your claim that "the world ends each instant of time". The monist view held around 500 BC by Parmenides was last challenged playfully by Zeno of Elea (c. 490–430 BC) who teases us with paradoxes resulting from attempts to fragment the progression of Time. Such fanciful notions have since been resolutely disposed of by such undoubted authorities as Aristotle "Time is not composed of indivisible nows any more than any other magnitude is composed of indivisibles." who is echoed by Thomas Aquinas "time is not made up of instants any more than a magnitude is made of points". Philvoids (talk) 14:13, 2 April 2025 (UTC)

QM and its many interpretations is daunting. Nevertheless, I take comfort in the notion that the big whirl's demise can be witnessed before desserts at Milliways. Modocc (talk) 13:07, 3 April 2025 (UTC)

April 2

Networks: centering centrality

https://arxiv.org/abs/2503.19681

"Here we propose a new adaptation rule for periodically driven complex elastic networks that accounts for the effect of short-term pulsatile dynamics on the remodeling signal at long time-scales. ... Specifically resonant frequencies are shown to prioritize the stabilization of fully looped structures or higher level loops proximal to the source, whereas anti-resonant frequencies predominantly stabilize loop-less structures or lower-level loops distal to the source. Thus, this model offers a mechanism that can explain the stabilization of phenotypically diverse loopy network architectures in response to source pulsatility..."

What's the networking term that describes this global-proximate characteristic of "higher level loops proximal to the source"? Also, does it include the extra-loopiness the authors put alongside it? I suppose they do seem to go together.

Gongula Spring (talk) 20:19, 2 April 2025 (UTC)

April 3

Is GPU variant and model number/product code the same thing? And can the two terms be used interchangable?

For reference

• https://www.techpowerup.com/gpu-specs/geforce-gtx-1070-ti.c3010 (GPU Variant: GP104-300-A1)

For context on Wikidata we are trying to figure out how to list the GPU variant on items about graphics cards. The only property to use i can think of is model number/product code but i am unsure if this the correct thing to do Trade (talk) 05:03, 3 April 2025 (UTC)

The computing section of our reference desk may be a better place for this question.  ​‑‑Lambiam 07:40, 3 April 2025 (UTC)

April 5

Dark matter and Z^0

Recently, I have read that there is a hypothesis that dark matter might consist of a particle which is its own anti-particle and when two of them meet they annihilate to form an electron-positron pair. This cannot be mediated by a virtual photon since only charged particles interact directly with photons and dark matter cannot be charged since it would not then be dark, but visible instead. So could it be mediated by a virtual Z^0 particle which would then decay into an electron-positron pair? JRSpriggs (talk) 19:25, 5 April 2025 (UTC)

Why don't trains sometimes have wheel humps?

Like buses and pickup trucks. Sagittarian Milky Way (talk) 21:15, 5 April 2025 (UTC)

What do you mean by 'wheel hump'? AndyTheGrump (talk) 21:26, 5 April 2025 (UTC)

The bump in the floor that hides a wheel. Sagittarian Milky Way (talk) 21:33, 5 April 2025 (UTC)

If you are referring to conventional passenger trains, the floor level is well above the tops of the wheels, which are generally on bogies. Same for most flatbed freight wagons. Given the need for bogies to turn, you'd complicate the internal layout, with very little benefit in terms of extra height. And with regard to passenger transport, you generally build new stock to suit existing platform heights - you wouldn't want a step down into the carriage.

There may possibly be trams and/or metro stock where the floor is lower than the tops of the wheels, but as far as mainline rail goes, the loading gauge allows plenty of height. AndyTheGrump (talk) 21:54, 5 April 2025 (UTC)

To add to the above, one exception to this seems to be for double-decker coaches, which are often built with the lower floor dropped down below the top of the wheels, between the bogies. Presumably the benefit of extra passenger space is seen to outweigh the obvious accessibility issues. AndyTheGrump (talk) 22:11, 5 April 2025 (UTC)