Wikipedia:Reference desk/Archives/Science/2019 April 23

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April 23

Seasonal day length variation

Which function describes the seasonal variation in day length? Looking at my own city's pattern [1] around the 46th parallel I used to think the variation was sinusoidal, mostly because it's slowest around the solstices and fastest around the equinoxes. However looking at places above the (Ant)Arctic Circle [2] [3] the pattern reverses and the rate of change is the slowest around the equinoxes. 93.136.1.73 (talk) 17:54, 23 April 2019 (UTC)

This is, rather straightforwardly, called the equation of time. --Jayron32 17:58, 23 April 2019 (UTC)

I should clarify that the name of the concept is straightforward. The concept itself is quite complex. --Jayron32 18:00, 23 April 2019 (UTC)

I'm talking about day length (sunset time minus sunrise time), not solar noon time. 93.136.1.73 (talk) 18:02, 23 April 2019 (UTC)

The equation of time can also be used to estimate the sunrise and sunset data for any location. See Analemma, which is the graphical representation for the equation of time at any one point on earth. Using the Analemma (derived from the equation of time) the length of the day can be calculated, and the article even gives a method for doing so. --Jayron32 18:09, 23 April 2019 (UTC)

Uhh, having a hard time picturing this. Has someone put up a formula for this? I don't care if the formula is complicated, I studied math. 93.136.1.73 (talk) 18:39, 23 April 2019 (UTC)

This webpage has both a javascript applet that will do the calculation for you, as well as a discussion of the math you could do yourself if you were so inclined. You can also read the Wikipedia article titled Sunrise equation which is the same math he is doing on his webpage, but more detail. (note: though it is called the "sunrise" equation, the article also discusses the small modifications necessary to also calculate sunset.) If you want the length of daylight, you do sunrise-to-sunset on the same date. --Jayron32 18:51, 23 April 2019 (UTC)

Thanks, I think I've figured something out with that. 93.136.1.73 (talk) 19:44, 23 April 2019 (UTC)

The biggest reason why the change is faster as you go away from the equinox in that example is that the sun was approaching its "up all day" status. As it appears to dip less and less beyond the horizon, even the slightest change in position in the arc makes a huge difference in the length of time it is above vs. below the horizon. Now to be fair, it looks like it's already "up all day" and still near the equinox ... and the length of day certainly isn't going to change much now, until well after the solstice! Wnt (talk) 13:16, 24 April 2019 (UTC)

Universe

If the universe decided to stop expanding and start contracting, how hot could it get on the way down? Or would it just disappear into its own black hole?80.2.20.155 (talk) 21:41, 23 April 2019 (UTC)

I'm still curious about whether the universe has the capability of "deciding" something. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:47, 26 April 2019 (UTC)

Black holes

Bearing in mind the number of discovered and postulated black holes in the universe, when the universe decides to stop expanding and shrinks, will all the black holes eventually coalesce to form one gigantic humunggoys never to be seen before or some one absolute giga mega giga tera ton massive black hole? If so, where does all that mass go? Does it sprout another big bang in some other 'place? Or does it just fixed up and die?80.2.20.155 (talk) 21:51, 23 April 2019 (UTC)

Black holes slowly evaporate. This is an incredibly slow process for the black holes observed so far, and is actually slower the bigger the black hole is. Nevertheless current wisdom has it this will happen to all black holes eventually, since it's believed the universe's rate of expansion will keep accelerating (unless I've missed something new). In this case most black holes will never merge with one another. 93.136.1.73 (talk) 22:12, 23 April 2019 (UTC)

You might want to read Ultimate fate of the universe and Big Crunch. I'm rooting for the Big Crunch, heat death seems just too depressing to me :D 93.136.1.73 (talk) 22:15, 23 April 2019 (UTC)

The odds are good you won't be around when whatever happens happens. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:27, 23 April 2019 (UTC)

I think the "depressing" nature of heat death is rooted in a lack of imagination. At very long time scales, physical processes like proton decay may occur that we cannot presently observe. Neutrinos might cool and condense and start interesting chemistry. Black holes become short-lived interactions. In the same way, the 'brief moment' of the early universe involved a tremendous number of particle interactions, and who knows what people and thoughts and worlds existed within one brief instant of quark-gluon plasma? One set of laws of nature is given a chance to play out, before it is ushered off the stage to make way for a whole new act with whole new rules -- rules that were always there, but as irrelevant as the melting point of ice in the middle of a quark-gluon plasma. I doubt it ever stops. Wnt (talk) 13:08, 24 April 2019 (UTC)