Wikipedia:Reference desk/Archives/Science/2017 December 23

= December 23 =

The † symbol in biological nomenclature
In the course of editing, I've come across sources that place the † symbol in front of the name of an order or clade or family or genus in the biological nomenclature for organisms. Example: †Name. Here's a link to one such source:. I've been looking for a definition of what the symbol means, and have been coming up blank. Can anyone point me to its meaning? Thanks. --Tryptofish (talk) 01:40, 23 December 2017 (UTC)
 * I would presume it means "extinct" (compare https://species.wikimedia.org/wiki/Lepisosteiformes without the cross in your link and https://species.wikimedia.org/wiki/Semionotiformes with the cross). 78.1.153.199 (talk) 01:55, 23 December 2017 (UTC)
 * Yes, it means extinct, and the dagger symbol (with illustration) is also used (I don't see that in our markup palette) which is an inverted dagger that looks like a cross, except that the top is thick, like a dagger's handle. μηδείς (talk) 02:47, 23 December 2017 (UTC)
 * It reminds one of a tombstone, which seems fitting. ←Baseball Bugs What's up, Doc? carrots→ 04:17, 23 December 2017 (UTC)
 * Last sentence of Extinction's lede: "A dagger symbol (†) next to a species name is often used to indicate its extinction." -- ToE 12:00, 23 December 2017 (UTC)


 * Fun fact: the dagger &dagger; is also sometimes called obelisk. Some of you will now go "Oh!". —Tamfang (talk) 09:17, 23 December 2017 (UTC)
 * Oh? ←Baseball Bugs What's up, Doc? carrots→ 16:05, 23 December 2017 (UTC)
 * Another fun fact: &dagger; often marks the second footnote on a page, after asterisk. —Tamfang (talk) 09:11, 24 December 2017 (UTC)


 * I have added the dagger as a png file so one can see the normal figure when it is not printed identically to a cross, as often occurs in non-serif fonts. μηδείς (talk) 17:06, 23 December 2017 (UTC)
 * It is important to note that not all extinctions are the result of animals being stabbed to death. 2606:A000:4C0C:E200:B8D8:3FE9:323E:5312 (talk) 18:31, 23 December 2017 (UTC)
 * Okay, Spartacus. That's the second time in a week someone has made me snort out my coffee. μηδείς (talk) 19:00, 23 December 2017 (UTC)


 * Note the term "endaggered species". ←Baseball Bugs What's up, Doc? carrots→ 19:13, 23 December 2017 (UTC)


 * Thanks everyone! Both informative and entertaining. --Tryptofish (talk) 20:44, 23 December 2017 (UTC)

Can ultracold neutrons form into pairs of neutrons that would be proton-free nuclei?
Can ultracold neutrons form into pairs of neutrons that would be proton-free nuclei?\\\\ — Preceding unsigned comment added by 64.134.232.149 (talk) 01:41, 23 December 2017 (UTC)
 * Courtesy link: Ultracold neutrons —2606:A000:4C0C:E200:B8D8:3FE9:323E:5312 (talk) 04:05, 23 December 2017 (UTC)

??obviously I would know that article, you sarcastic discourteous linker. Doesn't answer question, but it could mislead others into thinking the answer was at that article. — Preceding unsigned comment added by 64.134.232.149 (talk) 04:32, 23 December 2017 (UTC) Hey I wrote the above angry reply and I'm really sorry for being like that. Just really hyper and paranoid yesterday. By the way though, my device won't let me do brackets for linking or even girlies for signing. Sorry again! — Preceding curly is spellchecked into girlies!unsigned comment added by 96.82.242.226 (talk) 23:36, 23 December 2017 (UTC)
 * "Courtesy links" provide access to article(s) mentioned but not already linked in the query; not intended as an answer. 2606:A000:4C0C:E200:B8D8:3FE9:323E:5312 (talk) 05:38, 23 December 2017 (UTC).
 * Yes; they're intended as a courtesy to other editors, not to the OP, who should arguably have made the link themself. An alternative would be to Wikilink the words in the OP's own text, but this would violate the convention that we don't alter another's post in any way. {The poster formerly known as 87.81.230.195} 90.220.212.173 (talk) 09:12, 23 December 2017 (UTC)


 * There's nothing wrong with modifying the header to include the link, that's the best place for it anyway, and headers are not the poster's property, per MOS. μηδείς (talk) 16:34, 23 December 2017 (UTC)


 * Our Dineutron page tells us that there is no attractive force, but it nearly exists. However in the case of dihelium it was supposed to not exist also, but was made. So I would not bet too much on non-existance. Graeme Bartlett (talk) 07:33, 23 December 2017 (UTC)


 * There should be some neutron electric dipole moment, though technically that would be a dispersion force at the Van der Waals radius I suppose.... or it would be, if nucleus-nucleus "noncovalent bonds" were a thing. Hmmm.  Also, while in theory molecules are defined by electrons, so no electrons means...  I suppose there is some very small chance that an electron + positron (virtual pair) exist near a pair of neutrons.  You might also say the neutrons would be brought together a little by Casimir effect, which is also a virtual particle effect ... but the metal plates in a usual Casimir effect aren't normally defined as a molecule.  But what if the virtual particles can exist in real orbitals for a moment, is that Casimir effect or something else?  No "orbitals" in a Casimir effect that I know of!  Obviously I'm in no position to answer this but I hope the links/ideas might be a starting point for further consideration.  But I'm a little off topic for the sort of nuclear interactions you're most interested in.  A search for dineutron observed pulls up a bunch of interesting papers like  but I'm not the one to rate their quality/believability.  P.S. neutrons have spin 1/2, so there should be two nuclear isomers of any given "dineutron", one with spin 0 and one with spin +-1/2; are both accounted for?  Wnt (talk) 14:51, 23 December 2017 (UTC)


 * To be fair, He2 is not so much a molecule as a van der Waals molecule. MO theory, or at least as used for He2, is focused on covalent bonding; which is a reasonable approximation for most "normal" molecules, but for something like He2 where no covalent bonding is possible and only the van der Waals interaction is feasible, it is clearly not the best approach. A similar idea is not inconceivable; the dineutron does become stable on the surface of neutron-rich nuclei (a pretty direct quote, but there's no sensible way to paraphrase this – it's a footnote to the paper, which is itself pretty interesting, being about the consequences a stable dineutron would have on BBN). Double sharp (talk) 05:12, 24 December 2017 (UTC)
 * Hmmm, this says "The dineutron, a member of the nucleon-nucleon isospin triplet, is a spin singlet". I would think that means that dineutrons are defined as made up of neutrons with opposite spins, and the ones with same-sign spins are called something else?  At best guess, those others would be less stable since spins ordinarily like to pair, so it may be something more obscure?  If we can clinch this we might be able to upgrade our article. Wnt (talk) 02:09, 25 December 2017 (UTC)

Ocean photographs
What is the deepest photograph that has been taken anywhere in the ocean? JohnDoom (talk) 14:15, 23 December 2017 (UTC)
 * With artificial lighting, the bottom of the Challenger Deep, part of the Mariana Trench. If you mean with sunlight, you'll need somewhere with very clear waters. LongHairedFop (talk) 14:38, 23 December 2017 (UTC)
 * Don't forget that neither artificial lighting nor sunlight are required for photographs of bioluminescent organisms.... TenOfAllTrades(talk) 20:55, 23 December 2017 (UTC)

Feynman Lectures. Exercises. Exercise 15-1 JPG 2
. .

It seems that paradox described in previous question on 17.12.2017 is that the observers can not see both ends of the ruler at the same time. My new question is: Is it possible to adjust clocks such that at coordinates x=x'=0 we have readings on clocks t=t'=1? From Lorenz transformation it is impossible, but why can't we adjust clocks by our wish in single point of space ?Username160611000000 (talk) 12:34, 30 December 2017 (UTC)

Weird space launch shot
There was a news story about a space launch that Los Angeles citizens reportedly thought was aliens arriving. Now I assume this is a bit of "product placement"; I would be flabbergasted if some of the photographers were not both paid and prepared in advance with an ephemeris. Even so ... how did a space launch generate this kind of blimp-like "structure" in the sky, with a bright glowing bit in the middle? I mean, if this was a shock wave it shouldn't have outrun the rocket ... I'd think... also, if it was that powerful a shock wave, why didn't it create a huge boom that would have been commented on in the article? Wnt (talk) 14:39, 23 December 2017 (UTC)
 * It's a rocket/missile contrail. A very similar trail was left after the launch of Russian RT-2PM Topol intercontinental ballistic missile which some folks also believed was an UFO. See also Petrozavodsk phenomenon, but there I'm unsure, as UFO arguments in that case are equally strong. Brandmeistertalk  16:05, 23 December 2017 (UTC)


 * This was a Falcon 9 launch. These are a lot more complicated than normal launches. After stage separation, the first stage quickly flips around through almost 180 degrees with nitrogen thrusters, and reignites 1-3 engines to cancel the downrange speed for lading (this particular stage didn't actually do a full landing, but still went through these phases). This means that the engine plumes of both upper and lower stage are firing 'into each other', which lead to all sorts of complex interactions you don't see in normal launches. The bright glowing bit is the first stage, either thruster firings, or most likely the boostback burn. Don't see why you assume there is product placement? Everybody carries a camera with them in their pockets these days. Only need <<0.1% of people to see it to get multiple videos. Easy enough, as the trajectory is visible from a major population centre. Fgf10 (talk) 16:14, 23 December 2017 (UTC)


 * Wnt, you are so gullible. Once again you have fallen for the CIA's propaganda.  This was not a failed private launch or a publicity stunt!  It was a NASA first-stage booster launching Stephen Paddock to rendezvous with last week's Earth-grazing asteroid, where he'll live until 'Oumuamua returns to defeat the Trump Dynasty rulers of the Planets of the Solar Federation in 2112. μηδείς (talk) 16:31, 23 December 2017 (UTC)
 * No, no, no... this is obviously part of the Left Coast Sheeple Project -- there must have been a small pocket of folks there who have not yet succumbed to the machinations of the liberal elite. 2606:A000:4C0C:E200:B8D8:3FE9:323E:5312 (talk) 19:24, 23 December 2017 (UTC)
 * Vonnegut, Trump, Tesla and Gorsuch? Of course that piece is as coherent as the ramblings of a schizophrenic in a full psychotic break.  I need an Excedrin. μηδείς (talk) 19:58, 23 December 2017 (UTC)


 * Our relevant articles for this launch: List of Falcon 9 and Falcon Heavy launches, Iridium satellite constellation. NSF article: SpaceX close out 2017 campaign with Iridium-4 launch.
 * The time and date of this launch was publicized over two month in advance. Here is Iridium's press release from 19 October.  Given the clear forecast and the launch time scheduled for shortly after sunset, space enthusiast boards were abuzz with expectations of a spectacular display, though the actual event exceeded most already high expectations.  If the local media failed to discuss the launch in advance and suggest that local residents consider checking out the show, then they dropped the ball. -- ToE 20:00, 23 December 2017 (UTC)
 * Hey, the local news here has lots of very important car chases to cover! Also who pays any attention to the local news anymore? We all get our news from Facebook, which takes care to not disturb us with anything outside of our personal bubbles. --47.157.122.192 (talk) 07:23, 24 December 2017 (UTC)
 * Breaking news: The crew of an arcraft have been offerd emotional and psychological support to help them come to terms with an  inccident  where their arcraft  recently  made physical contact with a UFO over  Scadinavior. Photo of damage.. The Inrernational Civil Aviation Authority  has issued a statment, to the effect,   that in order to avoid widespead concern and panic, it is not going to comment just yet untill all radar images of the collition have been anylised but assures the public that this UFO possesed  no danger to the general public as it never came lower than roof top level. Aspro (talk) 20:17, 23 December 2017 (UTC)
 * I think you meant to say: "Braking gnus: ecru oven irk raft of bin overt a motion'll end sigh collegic's a port...." μηδείς (talk) 03:23, 24 December 2017 (UTC)


 * I stand currected. I hefe-a a beet ouff truouble  translating zee  language-a ouff Swedes und Turnips intu Ingleesh. ispeceelly after sampling their Akvavit.. Bork Bork Bork! Aspro (talk) 13:12, 24 December 2017 (UTC)


 * As a So Cal resident, every time anything is launched from Vandenberg you have people freaking out. Breaking news: a lot of people are dumb and/or ignorant. --47.157.122.192 (talk) 07:23, 24 December 2017 (UTC)