Wikipedia:Reference desk/Archives/Science/2016 August 11

= August 11 =

Number 80+ in Ancient Astronomy
Do any numbers in between 80 and 85 (or thereabouts) hold any relatively important or relatively obvious meaning in ancient astronomy ? (i.e., other than there being 88 constellations, roughly half of which were unknown to the ancients). — 79.113.220.18 (talk) 04:18, 11 August 2016 (UTC)


 * 88: the anniversary at which Saturn returns (for the third time, approximate) Sagittarian Milky Way (talk) 04:33, 11 August 2016 (UTC)


 * 80: the anniversary when Jupiter and Saturn pass each other (the fourth time, approximate) Sagittarian Milky Way (talk) 04:37, 11 August 2016 (UTC)


 * 80: the number of years between 10 Venus cycles of 10 apparitions each (half as a morning star and half as an evening star, accurate to about 3 weeks) Sagittarian Milky Way (talk) 04:48, 11 August 2016 (UTC)


 * 79: the anniversary at which really good oppositions of Mars happen like 2003 AD and 1924 (but not as good as the perfect opposition which happens every x years (x being a specific 3-digit number about a quarter millennium long that I forgot). Maybe. (depends on how accurately they knew these things) Sagittarian Milky Way (talk) 04:45, 11 August 2016 (UTC)


 * 83 Earth years = 7 Jupiter years (minus a dozen Earth days or so). Sagittarian Milky Way (talk) 04:35, 11 August 2016 (UTC)


 * The Moon phases repeat every 76 years because it's 19 times 4. They also repeat every 29 days and change and every multiple thereof. Sagittarian Milky Way (talk) 04:57, 11 August 2016 (UTC)


 * A tad bit shy of 80, but Halley's Comet returned every 74-79 years in ancient times. StuRat (talk) 12:08, 11 August 2016 (UTC)


 * Which wasn't discovered until Edmund Halley well after ancient times. Sagittarian Milky Way (talk) 16:11, 11 August 2016 (UTC)


 * The comet was observed on several earlier appearances, and Halley is credited with determining that those are appearances of the same object. However, others may well have made that discovery before him, since prior to the scientific awakening, if a royal astronomer made such an observation, the thing to do would be to tell the king, and nobody else, as "knowledge is power".  The king could then use a prediction of the appearance of the comet as a means of demonstrating his supernatural powers. StuRat (talk) 16:22, 11 August 2016 (UTC)


 * Murphy's Law: You predict a comet 74-79 years afterward, enough years in advance so that the 5 year span is more impressive and Halley and another great comet show up 2-3 months apart and you didn't predict that. (like 1910). The comet comes from the same position each time only in heliocentric coordinates and that was one of Halley's 2 clues that it's all the same comet. An ancient astronomer would have to believe heliocentrism or be some spatial and pattern-finding genius to get that clue (correlating the central point or point of max goodness of a months long comet apparition which is not necessarily at perihelion or Earth closest approach and might be affected by whether it's very foreshortened or placed for maximum angular length to figure out that the comet always comes from the same constellation even though it's too dim to see then). They didn't do statistical frequency analysis of comet years in those days either I don't think. Sagittarian Milky Way (talk) 17:30, 11 August 2016 (UTC)


 * Even if the king only knew the return within 5 years, if he was smart he could still work that in to establish his own divinity. Something like "I ascended to the other realm, and asked the other gods for advice on when I should marry again, and they said they would send a sign, and it would be time when a comet crosses the sky".  Of course, the king might die before it happened, but then he wouldn't be as concerned about maintaining the myth of his divinity after that, and his heir might alter the story to say that this was the gods' way of telling him he should never marry again.  If 2 comets showed up in his lifetime, he could take that as the gods telling him he should marry twice.  StuRat (talk) 14:41, 16 August 2016 (UTC)


 * The concept the OP is asking about is Numerology, and they read Wikipedia's article on the subject, as well as use it as a search term to narrow it down. Here for example is some sources on the meaning of "80" in various numerological disciplines.  Not sure if you'd count them as "reliable", but it may be enough for the OP's purpose.  -- Jayron 32 12:23, 11 August 2016 (UTC)


 * No. I am talking about an actual astronomical ″thingy″ (cycle or time period, number of stars or constellations, etc.), more or less known to the ancients, and whose numerical value is roughly 82, 83, or 84. — 79.113.220.18 (talk) 12:59, 11 August 2016 (UTC)


 * Uranus takes 84 years to go around the Sun. Pity it wasn't discovered until almost the 19th century even though it can be seen with the naked eye. Sagittarian Milky Way (talk) 16:14, 11 August 2016 (UTC)


 * I suppose there might be some culture with 82, 83, or 84 constellations. It might be more likely in the tropics where less sky is forever hidden (or none at all). The most number of stars in the ancient catalog the Almagest in one constellation is 45 and that's a very good catalog. They could see more stars than that obviously but didn't bother cataloging more than I don't know, a thousand or so. By around 1700 they were bothering to go down to enough detail that there's 82+ (100+ in fact) stars in some constellation(s) but that is not Ancient times. This entire catalog can be seen with the naked eye on a moonless night before modern lighting so it's within the technology of the Ancients to make but Flamsteed used a telescope (maybe for more accurate positions?). Sagittarian Milky Way (talk) 16:39, 11 August 2016 (UTC)


 * The culture I am investigating has 13 + 21 constellations in the northern and southern hemispheres, much similar to Ptolemy's 15 + 21 constellations. — 79.113.220.18 (talk) 18:37, 11 August 2016 (UTC)


 * There was a culture I forgot what it was that liked to have small constellations. They were the kind of people that would call the sickle of Leo one constellation and the lion's butt another (maybe they liked having a name for each day of the Moon's path (27 or 28) and kept that size scale for the rest of the sky) The Ancient Greek culture we get the 48 ancient constellations from (15+21 must be Hipparchos or somebody pre-Ptolemy) is actually a bit more lumper than modern tastes. A few constellations were invented in modern times but were seen by the Greeks (like Leo Minor, Scutum, Lynx). Argo Navis was split into Puppis, Vela, Carina and Pyxis was invented to be Argo's compass. Moderns see a teapot and a teaspoon where Greeks only saw part of the Sagittarius constellation. The Coathanger was not a Greco-Roman constellation even though it's shape is very accurate as these things go, much straighter than Sagittarius' arrow on his bow. But some of these were invented after the 1750s when new constellations usually didn't "stick" anymore or 1930 when the official constellations were set so they'll never be official, only asterisms. Sagittarian Milky Way (talk) 21:12, 11 August 2016 (UTC)

What is the name of brain-fat and low-priority-energy-usage-fat?
I know that both Brain fat and sometime other fats like Lipomastic fat aren't beta-oxidised easily for energy, either by a natural mechanism (to preserve the brain) or by a metabolic problem (Lipomastia in Men).

What is the name of such Adipose tissue? Thanks. Ben-Yeudith (talk) 11:34, 11 August 2016 (UTC)
 * The fat in the brain is myelin. However, myelin is not usually considered adipose tissue.  Adipose tissue, FWIW, is divided into two types: white adipose tissue and brown adipose tissue.  In the brain, the myelin is primarily found in white matter, though other fat-containing cells (various types of glial cells) are also found in grey matter as well.  Brain-based fat deposits are not, it must be emphasized, the same as adipose tissue however.  This quora answer explains the difference well.  -- Jayron 32 17:44, 11 August 2016 (UTC)

Electron structure probing
Can someone access the following article by S. J. Brodsky and S. D. Drell Physical Review D 22, 2236 (1980) and extract some details about internal structure probing of the electron mentioned in the article? Thanks.--82.137.12.11 (talk) 14:51, 11 August 2016 (UTC)
 * If no one here can, try WP:REX. Its designed to handle EXACTLY these sorts of requests.  -- Jayron 32 15:37, 11 August 2016 (UTC)

Type: "dx.doi.org/10.1103/PhysRevD.22.2236" in the field on Sci-Hub website. Count Iblis (talk) 15:40, 11 August 2016 (UTC)

The article is available fully legally here: http://slac.stanford.edu/pubs/slacpubs/2500/slac-pub-2534.pdf Graeme Bartlett (talk) 22:24, 11 August 2016 (UTC)
 * I replaced your now-blacklisted link to the Sci-Hub website with a link to our article about it. DMacks (talk) 14:28, 4 December 2018 (UTC)

How does astrophysics determine the life-cycle of a star?
How can they scientifically conclude that a star will become a pulsar or a black hole? Or a white dwarf? I assume we are observing stars for a minuscule length of their lives. Besides the reasonable assumption that the mass of a star decreases with time, what makes us be so sure that our sun will become a red giant? --Llaanngg (talk) 18:38, 11 August 2016 (UTC)
 * see stellar evolution, which supports your assumption and then explains alternatives. Sun seems to have lots of analysis and cites. DMacks (talk) 19:18, 11 August 2016 (UTC)
 * A great deal of science relies on indirect observations, indirect does not mean uncertain or imprecise. We've never "seen" hydrogen, gravity, electrons, etc, but we've come up with ways to detect and test them. We might have never "seen" a star turn into a black hole, but we can see a whole bunch of stars, we've "seen" stars in formation and stars in demise, the only "presumption" is that all the other stars are somewhere along that journey, so we model where in that journey each star is and like a jigsaw puzzle, the pieces start making a pattern and falling into place. Sometimes we make a mistake and put a piece in the wrong spot, but eventually if enough of that puzzle is solved, someone will recognize the mistake and set it right. Vespine (talk) 22:33, 11 August 2016 (UTC)
 * Good analogy. Sagittarian Milky Way (talk) 00:21, 13 August 2016 (UTC)