Wikipedia:Reference desk/Archives/Science/2020 July 31

= July 31 =

Lizard species identification
This photo of a lizard in a quite rare and unusual pose is being nominated for Featured Picture of Wikimedia Commons. I need help from a lizard expert to identify the species. Is it a sand lizard (Lacerta agilis)? StellarHalo (talk) 02:43, 31 July 2020 (UTC)
 * Have you tried contacting the uploader (c:User:Сергій Мірошник)? --2606:A000:1126:28D:34C7:B325:D9B8:574 (talk) 03:25, 31 July 2020 (UTC)
 * (Warning: my Ukrainian is not best and definitely not a lizard expert :-) The first two words in the title are the animal's name. Uk wiki says ящірка прудка is indeed Lacerta agilis. The third word means "frozen" (as in "put your hands up"). 93.136.45.191 (talk) 03:51, 31 July 2020 (UTC)
 * I placed identification request in an Israeli facebook group devoted to reptiles. It may be a good idea to place the request in other groups. אילן שמעוני (talk) 08:28, 31 July 2020 (UTC)
 * I have posted a message at Wikipedia talk:WikiProject Amphibians and Reptiles which seems to be reasonably active. Alansplodge (talk) 13:09, 31 July 2020 (UTC)
 * It seems there is an answer, from the said facebook group:, Viviparous lizard
 * אילן שמעוני (talk) 13:34, 31 July 2020 (UTC)

Birds of a feather...?
In the context of avoiding predation, my own casual observation suggests that birds and insects in the open air are less likely than are fish in the open sea to use the strategy of social aggregation (i.e. flocking, shoaling) - is this true? If so, what might be the reason? PaleCloudedWhite (talk) 11:18, 31 July 2020 (UTC)
 * Lack of efficient predators in the air, for instance. Ruslik_ Zero 11:47, 31 July 2020 (UTC)
 * Also, more visibility in the air. Consider the problems faced by an ocean predator preying on schooling fish. Most of the time, no fish in sight. Occasionally, a large school with too many to catch and eat them all. The predator can't see schools unless they are close. Now move it to the air. The predator can see flocks of prey miles away. --Guy Macon (talk) 12:49, 31 July 2020 (UTC)


 * An exception is the European rabbit: "by living in groups, rabbits may reduce this risk because a foraging group can detect an approaching predator sooner (Bertram 1978), and each member of a group is less at risk of being singled out during an attack (Vine 1971)". More detail than you probably want is at Predation risk, cover type, and group size in European rabbits in Donana (SW Spain). Alansplodge (talk) 13:14, 31 July 2020 (UTC)


 * But do predators in the ocean use sight very often? My impression is that they don't. Dolphins, orca, etc. use echolocation at least to some extant, in the hunting of prey. Sharks use several sense other than sight, including electroreception, and famously have an exceedingly keen sense of smell. Matt Deres (talk) 22:25, 31 July 2020 (UTC)


 * Links: Flocking (behavior) & Shoaling and schooling.  Possibly somewhat relevant-ish articles: Collective animal behavior, Selfish herd theory & Aggregation (ethology) 2606:A000:1126:28D:CC33:9148:10E7:83BF (talk) 14:46, 31 July 2020 (UTC)


 * That selfish herd theory page is interesting. Compare this, from Selfish herd theory


 * "The basic principle governing selfish herd theory is that in aggregations, predation risk is greatest on the periphery and decreases toward the center. More dominant animals within the population are proposed to obtain low-risk central positions, whereas subordinate animals are forced into higher risk positions."


 * ...with this from Muskox:


 * "Muskoxen have a distinctive defensive behavior: when the herd is threatened, the bulls and cows will face outward to form a stationary ring or semicircle around the calves. The bulls are usually the front line for defense against predators"


 * I believe that Elephants also react to predators by putting the largest bulls on the outside of the herd and the babies in the center. This may have something to do with the fact that the bulls are basically invulnerable against predators. --Guy Macon (talk) 15:33, 31 July 2020 (UTC)
 * Looking at the selfish herd theory page, I notice that the species mentioned there don't seem to have the sort of larger, more powerful individuals that muskoxen or elephants do. No single individual (or even a small number of individuals) would be likely to be able to kill or run off a decent sized predator. Basically, rabbits or such do better to clump together pushing the weakest outward to be sacrificed to spare the herd, while elephants and such do better sending the biggest and baddest out to whoop the snot out of the attacker. Remember also that small animals tend to breed faster. Losing dozens of rabbits from a group would not take much time to replace, but losing one elephant calf puts a strain on the herd. --Khajidha (talk) 20:21, 31 July 2020 (UTC)


 * I question the premise of the question. If I look at purely the open sky, mostly the birds I see are predators like hawks and vultures scanning the ground and flocks of non-predatory birds (ducks, geese, seagulls, starlings, etc.). Do insects also swarm to avoid predators? According to the news, you'll be able to hear the answer for yourself next year. Matt Deres (talk) 22:35, 31 July 2020 (UTC)


 * From the study of bird species on islands, with or without predators, with their mainland counterparts, there are indications that a lack of predators leads to less flocking. Mikenorton (talk) 10:36, 1 August 2020 (UTC)

What modern genera names are only a subset of what its name meant before Linnaeus?
Like Lacerta, there must be lizards outside that genus that the Ancients would call lacertae. Sagittarian Milky Way (talk) 15:44, 31 July 2020 (UTC)


 * For the common names for animals used in Classical Latin or Ancient Greek texts it is generally not known precisely which (group of) species they referred to. Possibly, there was not even any overlap. For example, the genus name Haliaeetus comes via Latin from Ancient Greek ἁλιάετος, which is commonly translated as “sea-eagle”, but LSJ thinks it may have referred to the Pandion haliaetus or western osprey, which belongs to a different genus, Pandion. Eagles are actually a rare sight in Greece and Turkey. That makes it impossible to answer the question with any reasonable confidence. Another consideration is that today many more species are known than occurred in the regions where Latin was spoken. Take Latin rana, meaning “frog”. Many species in the genus Rana occur only in Japan or the Americas, so can we meaningfully say that the ancient Latin term included them? Or take the urial in the genus Ovis; would the Romans, had they seen one, even have recognized it as being an ovis, “sheep”? --Lambiam 17:43, 1 August 2020 (UTC)
 * So Ovis might be one of the genera that are supersets of the ancient common name and Haliaeetus may be one with no overlap, and there could be other genera that are Venn diagrams or identical circles, they don't all have to be subsets. Are there any Rana that look toady or otherwise not froggy? Did they even have a word for toad? If not then Rana probably is one but we'll never know for sure. Sagittarian Milky Way (talk) 01:25, 4 August 2020 (UTC)
 * The Romans had bufo for "toad" and rana for "frog". But like the English common names "toad" and "frog", these do not correspond to clades.  --Lambiam 13:44, 6 August 2020 (UTC)

Why is 5 a good number of rockets for the Saturn V and "many more" and "burns kerosene" good for almost anything Soviet?
If a non-central first stage motor fails without damage to other parts can they keep the it from pointing to bad directions with tricks like vanes, at least for long enough to safely escape? How close to 100 percent of the central first stage motor's intended burn needs to happen to complete the Moon landing or Vostok/Voskhod/Soyuz mission? If it fails gracefully (is that possible?) What's the first difficulty that limits the maximum size of buildable rocket motors? Whether they'd have a practical and risk-averse use or not, what's the ultimate buildability limiter? Would the sound waves crack or unweld something or it'd have to be too thick from the square-cube law or what? If it has to be beefy enough to work 2 smaller engines with half the thrust might become lighter too despite the probable higher total surface area. Could the Soviet moon rocket with buttloads of liquid oxygen/kerosene motors be built today by NASA or Russian NASA (not that they want to) or is the chance of a bad motor preventing mission objectives still too high even for unmanned? Sagittarian Milky Way (talk) 17:04, 31 July 2020 (UTC)
 * SMW, I can dimly discern at least 7 separate questions without obvious simple answers, mixed with a good deal of questionable assumptions, in your semi-coherent ramble above. I'm not sure that it's easily addressable by a Ref Desk such as this rather than by, say, an extended discussion at some spaceflight-related discussion group. Do you want to try again with a more limited and rigorously defined question? {The poster formerly known as 87.81.230.195} 90.200.132.105 (talk) 20:23, 31 July 2020 (UTC)
 * What caused the Saturn V first stage engineers to decide 5 rocket bells was a good amount but Soviet heavy rocket engineers to decide many was a good amount? (technically most of them were boosters ejected before stage 1 to save weight and thus stage zero if one must have a number but that's still a lot of simultaneous rockets).
 * 2. If a rocket not on the central axis fails is it designed to try to counter the asymmetric thrust with movable aerodynamic surfaces and/or proper thrust settings on other rockets, at least long enough to escape?
 * 3. If it has no countering asymmetric thrust function and only one rocket loses thrust but quickly and someone presses the abort button as soon as they detect the thrust loss/asymmetry will the crew live? Yes? No? Maybe?
 * 4. In the Apollo 13 film the central rocket lost thrust and they just burned the others longer, if another Apollo's central rocket stopped burning suddenly how soon would it have to stop for the Moon landing to be cancelled?
 * 5. Let's say Yuri Gagarin, how many percent of a normal burn would the central rocket need for him to orbit once?
 * 6. What about reaching Mir? How soon could the central rocket cut off?
 * 7. What are the most relevant practical engineering tradeoffs for more but smaller vs. less but more powerful?
 * 8. What limits the ultimate power of a buildable rocket nozzle? If you wanted to orbit a satellite filled lead with an impractical Tsar Rocket with only 1 nozzle per stage just for showing off like the Tsar Bomb what would limit you first?
 * 9. Is the Soviet N1 moon rocket reliable enough for commercial satellites if built again now? This was the ~0.1 Hiroshima scale explosion I think, too many rockets and parts to fail. It was early in the Space Age though. Sagittarian Milky Way (talk) 23:31, 31 July 2020 (UTC)


 * In answer to your Nos. 2 and 3, see Dramatic on-board video shows moment of Soyuz booster failure. Alansplodge (talk) 17:10, 1 August 2020 (UTC)
 * I can answer 8. The burning chamber and the nozzle experience extreme temperatures that requires both cooling solution (leading the cold fuel around) and specialized grafi-derevetives materials. It poses strict limit as to the maximum power a single engine can bear. אילן שמעוני (talk) 18:29, 1 August 2020 (UTC)


 * Related to 3, the US manned rockets had a Launch Escape Assembly (LSA) for just such a contingency. (E.g: see diagram of Apollo command module) --2606:A000:1126:28D:2145:DDE9:39C1:3E55 (talk) 21:12, 1 August 2020 (UTC)
 * I am aware, I did not realize the Russian launcher was only 4 boosters though, at least for lighter payloads. I thought it was more. The Soviet Moon landing rocket was a lot though. Looks pretty Soviet chic with all those boosters. Sagittarian Milky Way (talk) 01:46, 2 August 2020 (UTC)


 * In response to your first question, I'm going to start by posing another question. Why do you think the US used 5 combustion chambers at all for the Saturn V first stage? Or the second stage? After all, the third stage only had one. The answer to your question isn't that the US thought 5 bells were great and the Soviets thought 30 was good. Neither thought either was good or better. They were solutions around technical limitations. The Saturn V needed a certain amount of thrust to do its job, and 5 F-1 engines could do the job. Instead of 5 engines, each delivering 1.5m lbs of thrust, why not have a single engine delivering 7.5m lbs of thrust? It turns out that is an incredibly difficult thing to do. You need powerful enough fuel turbopumps, engine cooling, and combustion stability in the "bell." These challenges get more and more difficult. Where early rockets, for example, dealt with high heat by building out of temperature resistant materials, eventually, the engine heat is enough that it will melt through anything we have. So, you start looking to other solutions, like regenerative cooling, but even that has its limitations. So, eventually, you decide "I can't make a 7.5m lbs thrust engine, so I'll settle for 5 engines with 1.5m lbs of thrust." Soviet rocket technology in the 1960s wasn't as advanced as that in the US, so they couldn't build an F-1 class engine. The engines they could build, like the NK-15, were more limited, and could only deliver about 380k lbs of thrust. So, you need more of them, including the weight of associated turbopumps and plumbing, which means you need more still as that's more added weight each time. So, you end up with 30 weaker engines. This problem never fully went away for the Soviets/Russians. Even after the N-1 failure, while they got good at building large tubropumps, they weren't as good at dealing with the combustion stability in large "bells." So, we end up with designs like the RD-107 and RD-170, which both featured single turbopumps driving multiple combustion chambers (4 in the case of the RD-107, and 2 in the RD-170). Again, this isn't because the Soviets thought "multiple combustion bells per turbopump is better," but rather "we can build large turbopumps, but we can't build equally large combustion bells." It's still better to have fewer turbopumps, if you can, because they are heavy. So, a single turbopump driving multiple combustion chambers is the solution with the technology available. --OuroborosCobra (talk) 02:55, 2 August 2020 (UTC)