Wikipedia:Reference desk/Archives/Science/2018 December 5

= December 5 =

Battery eliminator for smartphones?

 * And why did you do that? It is an engineering problem, not a bit twiddling one. Greglocock (talk) 08:16, 5 December 2018 (UTC)

Celestial bodies named after congresspeople?
Is this list complete? Are there potentially any others than listed? Thanks Ab e g92 contribs 03:42, 5 December 2018 (UTC)

Multiple devices sharing single radio antennas
In pictures of Kowloon walled city, the rooftops are covered in different ariels/antennas. I know that different radio wavelengths and directionalities require different designs of antenna but if their goal is to receive the same signal/broadcasts is there any reason why all the television sets couldn't be connected to the same antenna? If multiple televisions shared the same antenna, would the signal each television received be weaker due to them sharing? — Preceding unsigned comment added by 185.230.100.66 (talk) 08:20, 5 December 2018 (UTC)
 * Yes, if multiple receivers are connected to the same antenna, the signal at each would be weaker. But having a central antenna used to be standard (IIRC even required by building codes) e.g. in Germany at the time when everybody would receive the same 3 (yes, it was a better time ;-) TV programs over the air. For large buildings, there would be a small amplifier to strengthen the signal before distribution. This makes the signal a bit noisier, but not by much. And I suspect so would the interference from a forrest of antennas.--Stephan Schulz (talk) 08:49, 5 December 2018 (UTC)


 * In what you see the building management is not organised enough to realise that a central antenna system would be cheaper and give a better signal. So instead each household puts up an antenna on the roof and drops a connecting cable down the side the the building to their window to have a lead in for the TV. Graeme Bartlett (talk) 09:52, 5 December 2018 (UTC)


 * In Kowloon Walled City there was no building management. That was the point. HenryFlower 11:45, 5 December 2018 (UTC)


 * That's the kind of place that they say is so crowded the rats have hunched backs. ←Baseball Bugs What's up, Doc? carrots→ 12:33, 5 December 2018 (UTC)


 * The Chinese think 50 symbols is a long sentence and the Americans think 50 per acre is a dense city. Sagittarian Milky Way (talk) 18:59, 5 December 2018 (UTC)

What antenna to use for Bluetooth in middle/upstairs of brick house?
I live in a two-story terraced brick house and I'd like to stream music from my PC to my Bluetooth headset anywhere in the house. What would be the best antenna design to do this? There are so many. The 5 dbi antenna that I have won't cut it. The PC is located in the middle of the house on the second floor (first floor in US English) so the signal needs to kind of go in two directions. I guess any antenna designed for 2.4-2.5 GHz is suitable for Bluetooth. Part of the problem is the weak PCB antenna on the headset but I'd like to maximise the power of my PC antenna before I open my headset up. Thanks. — Preceding unsigned comment added by 185.230.100.66 (talk) 10:47, 5 December 2018 (UTC)
 * WiFi headphones are available. WiFi has a greater reach than Bluetooth. I've never used WiFi headphones before, but I'd imagine you'd install a driver on the PC that acts as a sound card, but then sends the audio via your home router to the headphones. Out of interest, what are the internal walls of your house made of? LongHairedFop (talk) 11:37, 5 December 2018 (UTC)


 * I would like to be able to use the same headset with my mobile phone; I'm not sure whether my mobile phone would support using a WiFi headset for music and phone conversation?
 * The internal walls are a mixture of brick, lathe and plaster (I think the house was built around 1930-40) and plasterboard (aka drywall). — Preceding unsigned comment added by 185.230.100.66 (talk) 13:56, 5 December 2018 (UTC)

Also, could a [splitter like this one] be used to connect two e.g. patch antennas pointed in different directions? Since the patch antennas seem to have quite limited radiation pattern width, there shouldn't be much opportunity for destructive interference? 185.230.100.66 (talk) 17:44, 5 December 2018 (UTC)
 * Performance of an antenna depends on it being connected to a receiver (or transmitter) via a transmission line whose characteristic impedance matches both the antenna and the receiver input. The SMA adapters you linked are not matched power combiners but simple T-junctions that represent impedance discontinuity that will cause excessive signal loss due to high Standing wave ratio. Combining multiple Patch antenna to increase Antenna gain at a given frequency is possible but requires design of impedance- and phase- matched coupling lines, see the Inverted-F antenna example. DroneB (talk) 23:43, 5 December 2018 (UTC)

An angry person should breath faster or slower?
Normally, when a person is angry, physiologically his breath faster or lower? Or in other words, is the parasympathetic system works or the sympathetic system works? ThePupil (talk) 18:14, 5 December 2018 (UTC)
 * Faster heart rate and faster breathing go together. ←Baseball Bugs What's up, Doc? carrots→ 18:19, 5 December 2018 (UTC)
 * I think Bugs actually meant read this. -- Jayron 32 18:42, 5 December 2018 (UTC)
 * I had been wondering where the OP had been for the last five years. Heart rate and Respiratory rate also get into this a bit. We also have articles on Parasympathetic nervous system and Sympathetic nervous system. The way the question is worded, though, it seems to raise the question of how one "should" breathe when angry. Typically someone who's angry will be advised to consciously start breathing more slowly, to help calm down. ←Baseball Bugs What's up, Doc? carrots→ 01:23, 6 December 2018 (UTC)
 * I edited the wording in order to avoid the meaning that you suggested. Anyway, I understood that sympathetic system is the player when there are fast breathing or fast pulse (tachycardia). Isn't it? ThePupil (talk) 06:26, 6 December 2018 (UTC)

Sundials were more accurate than clocks
And they were used to set early clocks too. I don't think we can accept this as a source but they got it from somewhere. The various articles that would contain this information should be improved if we can find evidence the statement was true. History of timekeeping devices is featured and I can't believe a featured article wouldn't have this.— Vchimpanzee  •  talk  •  contributions  •  19:27, 5 December 2018 (UTC)


 * It makes sense, the first mechanical clocks didn't have minute hands and still had to be set often while sundials correct themselves when they reach a quarter hour slow or fast. Of course even in 1585 mean solar time was fake time and apparent solar time was the real time so a sundial being more accurate would be a tautology. Sagittarian Milky Way (talk) 20:05, 5 December 2018 (UTC)


 * Not really; it still had to be correctly made and aligned for its latitude (as mentioned in the cited comic strip, under the heading "Your Place In The Sun"). However, once that was done, then indeed it would be definitively accurate as long as apparent solar time was in use. --76.69.46.228 (talk) 04:05, 6 December 2018 (UTC)


 * Though their accuracy was reduced after sunset - or when it rained - oh and when it was foggy as well :-) MarnetteD&#124;Talk 05:24, 6 December 2018 (UTC)
 * And don't forget total solar eclipses! --76.69.46.228 (talk) 07:28, 7 December 2018 (UTC)


 * Sundials are by definition more accurate than clocks for determining current time (not elapsed time), because noon is defined as the time when the sun is in the south (or north). You have to set your clock using a sundial. There are some caveats, like apparent solar time versus mean solar time, your longitude versus the central longitude of your time zone and GMT versus UTC. You can correct for the equation of time, although the correction will change with the axial precession of the Earth's spin and the apsidal precession of the Earth's orbit, but even a simple sundial will never be off by more than about 20 minutes. There's no way an atomic clock can be that accurate 10000 years into the future, if only because without observations it has no way of knowing when to insert a leap second. PiusImpavidus (talk) 09:51, 6 December 2018 (UTC)
 * Well yes, but after 10000 years I would expect that, depending on what they are constructed from, even many sundials will have badly weathered, quite possibly to the point of being no longer functioning. PaleCloudedWhite (talk) 10:25, 6 December 2018 (UTC)
 * That assumes that for thousands of years somebody uses the sundial but doesn't maintain or repair it. --Guy Macon (talk) 18:22, 6 December 2018 (UTC)


 * More accurate for what purpose? For measuring the position of the sun in the sky?  That's tautologically true: that's what a sundial does.  For consistently measuring a period of time that has elapsed?  Possibly, for early rudimentary mechanical clocks, maybe.  But the SI definition of the second is universal and unchanging and does not depend on the peculiarities of the motion of a small chunk of rock around a star located far out on the arm of an otherwise unremarkable galaxy.  If I'm timing how long something took to happen, and trying to decide if successive such measurements would be accurately reproducible, I'll take the atomic definition, and any reasonably reliable mechanical representation of it, over watching a shadow drift across a disk any day.  I mean, if I'm trying to bake a cake, I want to know that the time I leave the cake in the oven would be the same in January as it is in June, and not have to correct my sundial for the peculiarities of my particular date and location on the Earth.  For that purpose, a sundial is a pretty inaccurate tool compared to even a rudimentary mechanical clock.  -- Jayron 32 19:12, 6 December 2018 (UTC)
 * Especially on a cloudy day. ←Baseball Bugs What's up, Doc? carrots→ 21:28, 6 December 2018 (UTC)
 * Just drawing a (24 hour) clock face around a vertical stick would have the crappiness you mentioned but for a proper sundial which deduces the geographic longitude of the Sun from its shadow it's actually pretty accurate. One method is a rod pointing at where the stars spin around (near Polaris) and a ring centered on the rod marked in hours and minutes. A sun hour is always at least ~59:59.2 and less than ~60:00.8 in SI. It is only the accumulation of these that builds up 16 minute errors, for timing a cake of even 6 hours long this would only be +/-5 seconds in theory. And if Tycho Brahe recorded planet positions to the accuracy of several minutes of arc and precision of like 10 seconds of arc with a house-sized protractor and his naked eyeballs maybe a 1 minute sundial isn't beyond 1300s technology (which would only need 2 millimeter accuracy for a 1 yard wide ring, thermal expansion doesn't affect protractors if they're one homogenous piece so the entire sundial could be made of the same material and I think things like ingot molds would prevent them from being unaware of thermal expansion). If you make the rod width 4.5 millimeters per yard of ring diameter the shadow will be about a centimeter fuzzy per meter of sundial size (~4 minutes) but the umbra will be only tenths of a millimeter wide per meter of sundial size making judging the center of the shadow easy. Readings near sunset would be up to ~2 minutes wrong from atmospheric refraction though. Still good enough for cake? But utter rubbish for timing a short race, counting heartbeats or mississippis would be better. Sagittarian Milky Way (talk) 22:35, 6 December 2018 (UTC)


 * A method of setting-up a sundial which requires no technology beyond a stick, is to repeatedly mark the length of the shadow cast by your gnomen (or stick), the shortest measurement will be north (or south if you are the wrong side of the equator). Alansplodge (talk) 18:26, 7 December 2018 (UTC)