Wikipedia:Reference desk/Archives/Science/2018 December 22

= December 22 =

When we laugh which part of the autonomic system works?
When we laugh which part of the autonomic system works? Is it the sympathetic or the parasympathetics system that takes place in this case? --ThePupil (talk) 02:45, 22 December 2018 (UTC)
 * I am not sure that the autonomic system is at works at all when humans laugh. Although laughter episodes do have influence on it as all other emotional events. Ruslik_ Zero 19:38, 22 December 2018 (UTC)
 * I found this and this pointing at transient sympathetic activity, though this might intimate that when the parasympathetic system is hypersensitive something else (bad) happens (but I haven't read it ... haven't really looked two carefully at the other two). Wnt (talk) 19:22, 23 December 2018 (UTC)

Looking directly at bright lights; what is the result called?
When you stare into a bright light and then look away, you experience the result of a sort of temporary bleaching of cells of the retina - what is that phenomenon called? Is there a single word or phrase to describe this? Thanks. --88.105.121.127 (talk) 06:39, 22 December 2018 (UTC)
 * Temporary blindness.  One astronomer (as an experiment) deliberately looked at the sun for several minutes and lost his sight as a result (he feared permanently, but it later came back).   After the 1999 eclipse hospitals treated a number of people who looked at it without filters.   Some of these people still have sight problems. NEVER LOOK DIRECTLY AT THE SUN . 94.2.25.22 (talk) 08:09, 22 December 2018 (UTC)
 * Less dramatically, there's afterimage. Rojomoke (talk) 09:00, 22 December 2018 (UTC)
 * Photokeratitis is known by a number of different terms including: snow blindness, arc eye, welder's flash, bake eyes, corneal flash burns, sand man's eye, flash burns, niphablepsia, potato eye, or keratoconjunctivitis photoelectrica. DroneB (talk) 15:05, 22 December 2018 (UTC)

Nonpolar vs apolar
In chemistry, what is the difference between saying that some molecule is apolar versus that it's nonpolar? I'm asking mostly because on en.Wikipedia, the two words redirect to different articles right now. – b_jonas 12:32, 22 December 2018 (UTC)
 * They have exactly the same meaning. In addition nonpolar (apolar) molecules are usually hydrophobic, so the first redirect. It should probably be re-targeted for consistency. Ruslik_ Zero 19:32, 22 December 2018 (UTC)
 * Just as a further detail that apolar/nonpolar should point to the Chemical polarity definition of the terms rather than the hydrophobe property, not all non-polar substances are hydrophobic. Or at best it depends if you consider structures that are transiently polar (even though on average non-polar), such as xenon that is a polarizeable single atom, or structures that can form strong hydrogen bonds to water, such as hexamethylenetetramine to give solvated polar clusters (is it still "the nonpolar molecule itself" that is present?). DMacks (talk) 06:32, 23 December 2018 (UTC)
 * That's a great example worth putting in the relevant articles hydrophobe and nonpolar. But I didn't quickly find a reference which, per Wikipedia rules, says something like "Some compounds can be both nonpolar and hydrophilic, such as hexamethylenetetramine..."  Can you think of something off the top of your head we could use to source this? Wnt (talk) 19:36, 23 December 2018 (UTC)
 * Thank you for looking into it. The xenon thing is surprising, but then, the neon group elements always turn out to be crazier than I had previously imagined.  – b_jonas 01:39, 29 December 2018 (UTC)

Eccentricity needed to produce seasons without an axial tilt?
If the Earth had no axial tilt, how eccentric would its orbit have to be, if the perihelion and aphelion were to produce a cycle of seasons as intense with respect to temperature as the real Earth has around 45°N and S? Neon  Merlin  22:28, 22 December 2018 (UTC)


 * I expect someone will be able to calculate the required eccentricity to produce a similar variation in insolation, but considerably more than the current value. There would, of course, be two summers and two winters per year.  The exact climatic effects would be difficult to predict with any accuracy, but there would be a much greater temperature gradient from equator (impossibly hot?) to poles (much thicker ice cap).   Dbfirs  23:23, 22 December 2018 (UTC)
 * There would not be 2 summers a year, the center of ellipses is not at the Sun. Sagittarian Milky Way (talk) 00:05, 23 December 2018 (UTC)
 * Sorry, you are correct, of course. My mental image was faulty.  My only excuse for such a silly error is that it was late at night!  Db<i style="color: #4fc;">f</i><i style="color: #6f6;">i</i><i style="color: #4e4;">r</i><i style="color: #4a4">s</i>  07:54, 23 December 2018 (UTC)
 * That article on insolation certainly conforms to all the checkboxes for user-hostility in math articles. It snows people under with an incredibly complicated derivation, then the moment it starts moving toward a conclusion, omits the conclusion and throws a curve ball with the ellipticity of the earth, then finishes with a numerical formula with no term for latitude.  I honestly feel like one of the big textbook publishers has a couple dozen people on payroll whose job is to make sure Wikipedia math isn't usable across the board.  Don't even try to fix an article like that -- my expectation is all you get is a tirade of threats of being banned for daring to suggest anything could be wrong with it.


 * Still, if you do what all proper peasants should do and beg the Google gods for a page from a properly copyrighted textbook you'll get a prod toward a simpler explanation.  You take the 23.5 orbital declination and subtract (summer) or add (winter) that value from the 45 degree latitude of the example.  That gives 21.5 and 68.5 for the zenith angle at high noon.  Now take the cosine of that and get 0.93 and 0.37 respectively - that is how much the light is reduced by the angle during summer and winter.  The ratio of summer to winter is 0.93/0.37 = 2.53.  To get that by eccentricity, the sun would have to vary in distance by the square root of 2.53 = 1.59, i.e. 59% further away in winter than in summer.  (Plus the earth's minor eccentricity, which I doubt is simple addition but probably is negligible in the face of that)  Now for these purposes it doesn't matter how big the ellipse is - we were only asked eccentricity, and any variation in light can be dealt with by turning the sun up or down afterward.  So let's say the earth moves from (0,0) in summer to (2.59, 0) in winter with the focus at (1,0).  Now if my recollection of what eccentricity is is right, we can take the center of the ellipse at (1.30,0) and calculate the ratio of (1.30 - 1)/1.30 and get 0.23.  The article on orbital eccentricity says the ratio of aphelion and perihelion is (1+e)/(1-e) and that checks, though it would have been a royal pain to use it in a forward direction.  So I'm going to go with a figure of 0.23, noting that this is only the hypothetical top-of-atmosphere insolation at the summer and winter solstice and may not reflect a real climate (since after all, an elliptical orbit is a lot of winter and a little bit of summer) Wnt (talk) 04:43, 23 December 2018 (UTC)
 * Thank you for the calculation. I was too tired to attempt it last night.   <i style="color: blue;">D</i><i style="color: #0cf;">b</i><i style="color: #4fc;">f</i><i style="color: #6f6;">i</i><i style="color: #4e4;">r</i><i style="color: #4a4">s</i>  07:54, 23 December 2018 (UTC)