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October 26

Bacteria questions.

Do bacteria have an equivalent of sleep?

What do bacteria do for waste, can they eat their own waste, and can they eat the remains of dead bacteria? Assuming they have a mouth.

I know bacteria reproduce by splitting in half, so there must be a point where cutting it in half kills it vs. doesn't kills it. 67.175.224.138 (talk) 02:31, 26 October 2019 (UTC).[reply]

The answer to the sleep question is generally "No", but there are some day-night related activities with some bacteria.[1] ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:59, 26 October 2019 (UTC)[reply]

In relation to the second question, here's an article which includes the subject.[2] ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:02, 26 October 2019 (UTC)[reply]

And for the third, cutting a bacteria in half, supposing you find a cutting object of the relevant size, will always kill it. see Fission_(biology)#Binary_fission for the way it reproduce: this involves the creation of a new cell boundary inside itself, not really a cut Gem fr (talk) 16:23, 26 October 2019 (UTC)[reply]

Yes, "slicing" a cell exactly in half would involve rupturing its cell membrane, which kills the cell. This is true of any cell. Bacteria also have a cell wall, and several classes of antibiotics, such as the beta-lactam antibiotics, work by disrupting it, which either kills or weakens the bacteria. Cell division involves splitting the cell membrane and, if applicable, dividing the cell wall, in an orderly fashion. --47.146.63.87 (talk) 07:36, 27 October 2019 (UTC)[reply]

It's also likely that only one of the cuts will have a copy of the Circular prokaryote chromosome. So even if the damage could be repaired, only one part would be viable. Nil Einne (talk) 08:30, 27 October 2019 (UTC)[reply]

Cellular waste is disposed of either by simple diffusion or active transport. Bacteria aren't much different from your own cells in this aspect. A given bacterium can't "eat" it's own waste; that's what makes it waste, something the cell wants to get rid of. However, something that's waste to one species of bacteria can be food for another. Good examples are fermentation products, which can often be broken down further by other cells given the right conditions. (A familiar fermentation product is ethanol, or "alcohol", though the ethanol that humans consume is produced by yeasts, not bacteria.) --47.146.63.87 (talk) 07:36, 27 October 2019 (UTC)[reply]

There may be some exceptions to that, but they are dependent on specific conditions. Under starvation conditions, bacteria (and other organisms) will go through a biochemical pathway that does things like converting ATP/GTP down the pathway to adenine and guanine, which is then released into the surroundings (this could be called "waste"). After the reintroduction of nutrients, the pathway reverses to a salvage pathway that allows the production of ATP/GTP without the expense of de novo synthesis. Under these conditions, the bacteria are essentially "eating their own waste." --OuroborosCobra (talk) 20:25, 29 October 2019 (UTC)[reply]

October 27

Native Americans and Paleo-Indians

Since until around 18th-19th century Native Americans in the US and Canada had no or negligible genetic admixture from Europeans, does it mean they looked essentially the same as Paleo-Indians thousands years ago? 212.180.235.46 (talk) 22:59, 27 October 2019 (UTC)[reply]

Not necessarily. In the first place, different communities of Native Americans in different places look markedly different from one another, and we know that various of them have moved considerable distances over those thousands of years, both from their own oral histories, from archeological and genetic studies, and from the fact that some of them managed to spread all the way from Beringia to Terra del Fuego over the course of only a few thousand years. We have so far been able to distinguish at least 4 separate movements of distinct peoples from Beringia into the Americas, 2 of which ("UPopA" and "Ancestral B") remained in North America and the other two ("Ancestral A" and "Population Y") additionally spread to South America. (See for example 'People of the Ice: The Final Frontier', New Scientist 28 September 2019 pp 34–37.)

In the second place, distinct human populations with distinctive looks can change markedly (to the extent of forming and disappearing) in periods of the order of a thousand years (I've read this in respectable historical works, but can't find a reference at this moment), due to genetic drift, microevolution from adaptation to new climates and other conditions, and doubtless other factors, even in the absence of any mixing with other populations, whether neighboring or from further afield.

Long story short, some of them might, others probably don't, it's complicated, and it's not easy to tell. Any more knowlegeable commentators who can enlarge on (or refute) the foregoing? {The poster formerly known as 87.81.230.195} 90.200.41.118 (talk) 23:37, 27 October 2019 (UTC)[reply]

I cannot source it, but I remember watching a documentary on this question. At one place, the old buried bodies investigated by archaeologists had quite different morphology from the current native dweller, so the first thought was they were different people (which was ground for the bodies to be kept in museum, denying the claim of the natives that the bodies were theirs) ; when genetic tests became available, it was shown that they actually were the same people (and the natives claim was granted). It doesn't take much genetic change to significantly alter the phenotype, enough to look quite different Gem fr (talk) 18:34, 28 October 2019 (UTC)[reply]

This was the source of the error in thinking that Kennewick Man showed Caucasian features. Paleo-Indians had facial features that were much more robust than modern Native Americans; essentially they were cavepeople. The same sexual selection that operated on ancient Europeans to evolve more gracile features also operated on Native Americans. Basically put, people with gracile faces got to have more babies earlier in life. Heaviside glow (talk) 20:20, 28 October 2019 (UTC)[reply]

It could very well be that the documentary I watched was about Kennewick Man indeed, thanks for the ref Gem fr (talk) 08:00, 29 October 2019 (UTC)[reply]

Native Americans had European admixture from 1492 on. It did not start in 1700. Edison (talk) 02:24, 29 October 2019 (UTC)[reply]

Wrong again. They had European admixture from the year 1000 onward. --Jayron 32 18:23, 29 October 2019 (UTC)[reply]

Although the Vikings were indeed in Greenland for several hundred years at that time, as were Inuit, the evidence from this 2015 paper [[3]] is against any genetic admixture at those times. This is based on a sample of 10% of the present Greenland population. One problem for the analysis is that the later colonisation of Greenland was also by Scandinavians, but the lengths of Scandinavian DNA in modern Greenland genomes (which should tend get shorter over successive generations thanks to recombination) are no shorter in areas where the Vikings had lived. It is quite conceivable that Vikings and Inuit kept themselves largely apart, for a variety of good reasons. Jmchutchinson (talk) 19:35, 29 October 2019 (UTC)[reply]

It's possible, but in general when people are in the same area for any period of time, there's going to be some skoodlybooping. Unless the contacting populations are very small, and/or their contact is very brief, someone is going to get some action. --Jayron 32 20:30, 29 October 2019 (UTC)[reply]

October 29

Solvation number

Can someone with access to the content of the book Metal ions in solution (1978) by John Burgess verify the chapter 5 of this source to see whether the method mentioned at talk:Solvation shell#Unsourced is also presented among the methods included in this chapter of this source? Thanks!--109.166.131.34 (talk) 20:50, 29 October 2019 (UTC)[reply]

Chapter 5 lists the values of solvation number as determined by compressibility, in particularly by using ultrasonics. Chapter section 4.3.2 is titled "Compressibilities" says that Passynski's equation is used. However the equation is not given in the book. The equation reference is "Passynski, A. Acta Phys.-chim 8 385 (1938)" which I cannot find. https://doi.org/10.1143/JPSJ.16.761 makes use of this ref and may be relevant. Graeme Bartlett (talk) 22:26, 29 October 2019 (UTC)[reply]

It appears that the Passynski reference is from a Soviet journal Acta Physico-Chimica URSS which hasn't been digitized being thus available only off-line.--109.166.131.34 (talk) 13:02, 30 October 2019 (UTC)[reply]

How about the content of the following book Aqueous Solutions of Symple Electrolytes, H. L. Friedman, Felix Franks and especially chapter 1 Ionic hydration? Could it contain details re Passynski equation, including derivation?--109.166.131.34 (talk) 13:13, 30 October 2019 (UTC)[reply]

I don't have that book, but online it does not mention Passynski's equation. Its talk about compressibility is related to thermodynamics rather than calculating the solvation number. It does have a formula on page 73 in section 4.3.1: summarised as: Isothermal compressibility = -8.307 × charge² /(Pauli crystal radius + Δ) ml Å bar⁻¹ mol^⁻¹; Δ is some sort of length measurement of the solvation sphere, and can be 0 Å.[4] Graeme Bartlett (talk) 23:23, 30 October 2019 (UTC)[reply]

October 30

Cadmium fumes from molten solder

When heated above 321 °C cadmium melts and cadmium oxide fumes present a hazard to health. My question is, if cadmium is part of a solder alloy which is heated to, say, 220 °C and has a melting temperature far below this, would it also be expected to produce significant cadmium oxide fumes? --88.106.182.98 (talk) 08:50, 30 October 2019 (UTC)[reply]

"significant" is a tricky word to interpret... For professional use, there will be norms, fume hood would be compulsory, etc. For unprofessional use, really dangerous device would be forbidden in developed countries, and if some caution is required it would be mentioned. You may find this [5] of help. In any case, if you are worried just use a fan blowing fumes away (this will work for any fume) Gem fr (talk) 11:21, 30 October 2019 (UTC)[reply]

What sort of solder involves both cadmium and a melting point so low? That's the lead-tin soft solder range and they just don't include cadmium – and for a long time now, almost nothing includes cadmium.

Now, silver solder used to contain significant cadmium, but that has been removed for a couple of decades now. My own workshop is full of the old stuff, snapped up cheaply when it changed over! But the temperature there is much higher. The only commonplace solders nowadays which contain cadmium are those sold for DIY or home repair of aluminium (or zinc) alloys.

There are a couple of hazards from silver solder. Fumes from cadmium metal in molten solder aren't really a big one. Firstly, silver soldering is done with a gas torch, which is much hotter itself than the melting point of the solder. If the flame is somewhat oxidising (rather than neutral), then cadmium may be oxidised on the surface (it will do so preferentially to the less reactive silver). This is now cadmium oxide, and (as always for metals, especially beryllium) that's a much less mechanically stable material than the metal. The oxide may be brushed off as a powder (not fumes) and the oxide can be absorbed by the body quite easily. Secondly, fluxes for hard soldering and brazing often include sodium fluoride and the fumes from heating that can include oxygen difluorides, which are pretty nasty in themselves. Andy Dingley (talk) 11:47, 30 October 2019 (UTC)[reply]

Solder alloys include a sortable table, some of them with Cd are indeed very low MP Gem fr (talk) 14:49, 30 October 2019 (UTC)[reply]

Those are alloys like Woods metal, which are barely solders but are instead specifically-formulated low-melting point materials for other uses. Nor are they particularly common. Another group are the cryogenic solders, which aren't seen outside a physics lab. Nor does anyone use Cerrobend as a cryo solder since the 1950s! We have proper equipment now, even in my day, we're not sealing glassware with sealing wax either.

The only one which might turn up in a "household" context would be the easy-flux solders for aluminium or zinc, like Lumiweld. Andy Dingley (talk) 17:42, 30 October 2019 (UTC)[reply]

Low temperature solders like LowMelt and Chip Quik are used for desoldering sensitive electronics components and there are alloys to do this which contains cadmium (and others which don't). The soldering iron temperature for these operations would be set to about 210 C. 88.106.182.98 (talk) 00:29, 31 October 2019 (UTC)[reply]

Looks like the Solder alloys article need some fixing, then. I lack expertise to do that, if you have, please proceed. Gem fr (talk) 04:42, 31 October 2019 (UTC)[reply]

When eggs go bad

A hard-boiled chicken egg occasionally has a small area of brown liquid inside, usually in the white of the egg. What is this ? SinisterLefty (talk) 19:01, 30 October 2019 (UTC)[reply]

Incubating the egg might reveal it to be fertile, in which case you can serve it as Balut (food). DroneB (talk) 19:23, 30 October 2019 (UTC)[reply]

Does that still work once the egg is cracked open? ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:26, 31 October 2019 (UTC)[reply]

Yes, just duck tape over the quack. DroneB (talk) 14:04, 31 October 2019 (UTC)[reply]

DroneB: Did you know this would actually work? There was a video of someone incubating a chick all the way to ""hatching"" in a wine glass without the shell. Forget where tho. Also nice pun --MoonyTheDwarf (Braden N.) (talk) 21:08, 31 October 2019 (UTC)[reply]

A company also took advantage of this frequent misspelling: [6]. SinisterLefty (talk) 22:17, 31 October 2019 (UTC) [reply]

Does anyone have good sources for this process of taping a crack? I am trying to develop Draft:Egg repair. Graeme Bartlett (talk) 21:13, 31 October 2019 (UTC)[reply]

Video is described here: [7] DMacks (talk) 21:25, 31 October 2019 (UTC)[reply]

Growing chick embryos in vitro. A few survive up to 15 days, see pictures. DroneB (talk) 22:18, 31 October 2019 (UTC)[reply]

This is unlikely if it's a typical commercial egg. Egg-laying hens are not kept around males; the eggs are unfertilized. The chance is slightly higher if the egg is from a free-range farm where a rooster could possibly get to the hens, but still not very high. Egg farmers don't want non-castrated roosters around layer hens because they can be aggressive, and multiple roosters will fight over the hens. --47.146.63.87 (talk) 23:40, 31 October 2019 (UTC)[reply]

These are just basic eggs, not free-range or anything fancy. SinisterLefty (talk) 02:31, 1 November 2019 (UTC)[reply]

One other bit of info, the last bad egg did not float in water before it was hard-boiled. (I do the float test to find rotten eggs and discard them, prior to cooking.) SinisterLefty (talk) 07:36, 31 October 2019 (UTC)[reply]

October 31

Can neutrinos collide with each other?

If so, how often would this happen? Would collision be more common among extremely low energy neutrinos?Rich (talk) 07:28, 31 October 2019 (UTC)[reply]

Apparently so. --Jayron 32 11:37, 31 October 2019 (UTC)[reply]

Destructive interference and conservation of energy

Two waves that move in opposite directions meet and for a single moment cancel each other. When dealing with, say, water or sound waves, at the moment when two waves interfere and cancel each other, energy is preserved in the medium momentum. The water are briefly flat, but the water molecules are in motion. Where to the "missing" energy when electromagnetic waves meet goes? -IlanMa

The energy is to be found where the waves reinforce each other. The fields add together, and the energy/power is proportional to the square of the field. So you might think that with two waves you get four times the power, but that only compensates for the destructive interference. Graeme Bartlett (talk) 21:10, 31 October 2019 (UTC)[reply]

If one of the waves has positive amplitude and the other negative, there will be no reinforcing. Also, conservation of energy has to be satisfied for each point in time, and not be an average over an interval. The answer must be something else. אילן שמעוני (talk) 03:54, 1 November 2019 (UTC)[reply]

If you could launch two waves from the same point with opposite "amplitude" then they would cancel each other out. What would happen is that energy would go from one source which had current and voltage in-phase, to the other source that had the current opposite to the voltage. With alternating waves they will often be averaged over time to measure the power. But if you want instantaneous in time then you will get a sinusoidal power transferred. The energy will move from one point to another at the speed of light, and where there is reinforcement, the energy will travel there, and away from the cancellation area. Graeme Bartlett (talk) 10:58, 1 November 2019 (UTC)[reply]

Not necessarily. Take the most "primitive" way to create electromagnetic wave - simply to shift the position of a statically-charged object. Take 2 such objects, and shift them perpendicular to the line between them, but in opposite directions. You'll get an two electromagnetic waves propagating, with opposing amplitudes. The wave form will be whatever you desire (determined by changing the velocity during the shift). Anyway, I still think that satisfying energy conservation over time is not enough. It must be conserved for any given time, down to Plank time. I may be missing something obvious, but so far I see no answer to this conundrum. It's not that I believe that Mr. Anonymous found a breech in physics, but I still can't see any direction towards an answer. אילן שמעוני (talk) 11:19, 1 November 2019 (UTC)[reply]

Moving a charge to excite an electromagnetic wave requires adding work to the otherwise-closed system. In this scenario, energy is conserved only when you correctly account for the added work. Nimur (talk) 14:23, 1 November 2019 (UTC)[reply]

In the case of two moving charges moving in opposite directions close to each other, energy has to be put in when they approach each other, and it is extracted when they separate. So they will bounce backwards and forwards like a spring, and no energy will be radiated, it will just come in and out of the system via the "antenna". Graeme Bartlett (talk) 21:28, 1 November 2019 (UTC)[reply]

When two waves traveling in opposite directions meet and interfere as you describe, the result is called a standing wave. With water or sound waves, for a single moment the displacements cancel out, and the velocities add. A little later, the displacements add, and the velocities cancel out. With electromagnetic waves, something very similar happens when you include both halves of the word electro-magnetic. If at a given moment you make the electric fields cancel, the magnetic fields will add, and vice versa. --Amble (talk) 05:33, 1 November 2019 (UTC)[reply]

You seem to assume that the oscillation in the magnetic field in 180 degrees phase shift from the electric field. I see no reason to assume that. The 1st diagram in Electromagnetic radiation, for example, illustrates perfect same-phase on both fields. In such case your suggestion fails. Anonymous already stated that the situation with in-medium waves is known to him (I didn't know up to this point, btw) and drawing mysterious hints. Last but not least, Standing wave is a totally different phenomenon - I asked what happens in a single pulse, which fits the original question, and will not produce standing wave. A knowledgeable answer is required. אילן שמעוני (talk) 07:10, 1 November 2019 (UTC)[reply]

Why not review Poynting's theorem in your favorite book on electrodynamics? In Griffiths' Electrodynamics, this is section 8.1.2 (Work) and 9.2.3, (Energy and Momentum in Electromagnetic Waves). To put it bluntly, the math is quite difficult, but it is well understood by knowledgeable physicists - it just takes some effort to study it. Nimur (talk) 13:54, 1 November 2019 (UTC)[reply]

In the standing wave, an equivalent wave is travelling in the opposite direction as the forward wave, and the electric field is flipped compared to the forward travelling wave if there is a short circuit at the end. If there is an open circuit then the magnetic filed will flip 180° at the termination. You can use a right hand rule to work out the direction of travel given a magnetic and electric field. If one is switched 180°, the the direction of travel will also switch 180°. ~~In this case the energy is quadrupled where the waves reinforce, and zeroed where they cancel.~~ The average is double because you have two waves, one forward and one reverse. Graeme Bartlett (talk) 10:37, 1 November 2019 (UTC)[reply]

Take note that electricity flow through a conductor, unlike photons in vacuum, has a medium. It's just the same as the water/sound/spring - the medium movement (the electrons in the conductor) take care for energy preservation, so trying to sort this puzzle through electrical signals thought experiment is unlikely to provide an answer.::::EDIT: I never thought such simple trivial question would give me such pain. אילן שמעוני (talk) 11:26, 1 November 2019 (UTC)[reply]

...Have you ever worked a problem in mathematical physics before? Simple questions often have alarmingly complicated implications. Part of formal education in physics is the repeated re-working of difficult standard-form equations in trigonometry, analytic geometry, and calculus, so that we can rapidly reduce to a previously-solved and easily-recognized standard form. After a few years and a couple thousand iterations solving for sinusoid coefficients, you too can follow along with the abbreviated shorthand notation that summarily executes the same equation-solving methods, and you start to focus only on the nontrivial parts. Nobody knowledgeable says that physics is easy. Nimur (talk) 14:15, 1 November 2019 (UTC)[reply]

Two similar electromagnetic pulses of the same amplitude travel in opposite directions towards each other. If their E-fields are aligned, then their H-fields must be opposite (because the direction of propagation is E×H). The energy density at any point in space is (εE²⋅+μH²)/2. For each pulse, half its energy is in the E-field and half in the H-field (because |E|/|H|=Z₀=√(μ/ε)). When the pulses meet, the E-fields add and the H-fields cancel. The total energy in the E-field doubles (because the square of sum is twice the sum of the squares). The total energy in the H-field is reduced to zero. The total energy in the E- and H-fields together is therefore conserved. catslash (talk) 14:04, 1 November 2019 (UTC)[reply]

For a pulse travelling along a conducting wire, the energy is not in the movement of the electrons (or not much is). The energy is still mainly in the electric and magnetic fields. The mobility of the electrons (imperfectly) prevents the fields from entering the conductor (because the electrons move to cancel the field). Consequently, the fields carrying the energy slide along the outside of the wire like a bead. catslash (talk) 14:28, 1 November 2019 (UTC)[reply]

Quite right - and in the even more generalized statement, it is only meaningful to calculate the energy of an electromagnetic wave when you correctly manage the bookkeeping for both fields, plus the energy in any coupled charges and currents. In this fashion, because of the coupled fields, an electromagnetic wave is entirely dissimilar to a simple acoustic wave or a transverse vibration on a string: an electromagnetic wave is a coupled system: its field amplitudes are described by a different wave function and different propagation equation; its energy is defined by a combination of two, coupled, energized fields, related by our great and powerful friends: the Maxwell's equations for electromagnetic dynamics. Nimur (talk) 14:33, 1 November 2019 (UTC)[reply]

I want to see if I got this right, and I'll walk through each step seperately. I assume E-field is electrical, so the H-field is magnetic (usualy denoted as B)? אילן שמעוני (talk) 16:52, 1 November 2019 (UTC)[reply]

User:אילן שמעוני: I was responding to the original question, which posits two waves of equal amplitudes traveling in opposite directions. This is precisely a standing wave. The important thing is that you have to include the energy in both electric and magnetic fields, and it's not possible for both of them to cancel at the same time. This is similar to mechanical waves where you have to include the energy in both displacement and motion. No, I don't assume that the electric and magnetic fields are out of phase; it simply isn't relevant to the original question. --Amble (talk) 22:07, 1 November 2019 (UTC)[reply]

Salmon foam

After I cook salmon sous-vide, there's a white foam on top that solidifies when it cools. What is this, and is it healthy to eat ? SinisterLefty (talk) 22:27, 31 October 2019 (UTC)[reply]

Probably fat and gelatin from the fish. Fats will liquefy as they reach their melting points and then solidify as they cool; think of melting butter. I sometimes notice some foamy white stuff when I make salmon, usually by grilling. --47.146.63.87 (talk) 23:28, 31 October 2019 (UTC)[reply]

I was thinking either fats or cholesterol, but then the question remains, are those good fats and cholesterol I should eat, or bad fats and cholesterol to avoid ? Gelatin would be fine to eat, I assume. SinisterLefty (talk) 02:13, 1 November 2019 (UTC)[reply]

That depends nearly entirely on your BMI status. If your weight is of no concern, there is close to no reason not to consume fat and cholesterol. There is only weak correlation between cholesterol consumption and blood cholesterol. Over 90% of the blood cholesterol is produced in your liver. Overweight, on the other hand, has been shown again and again to be a serious health risk and to lower life expectancy. — Preceding unsigned comment added by אילן שמעוני (talk • contribs) 03:51, 1 November 2019 (UTC)[reply]

I get the impression that everyone should consume as much good fat and good cholesterol as possible, while minimizing bad fat and bad cholesterol. Not an easy task, though, as they are often mixed together. SinisterLefty (talk) 06:09, 1 November 2019 (UTC)[reply]

There are many publications here's one that there is little to no effect of cholesterol consumption on cholesterol in blood. Sure, high LDL levels in the blood are lethal, but you will have them with or without cholesterol consumption as your liver is the culprit. Unless you suffer from another condition that makes cholesterol consumption bad for you, you can munch on cholesterol to your liking.

The most prevalent condition that makes fat consumption a very bad idea is obesity. Across all food sources, fat contains most calories, double than pure sugar. אילן שמעוני (talk) 07:19, 1 November 2019 (UTC)[reply]

But that ignores the satiety effect of eating fats. If eating the sugar leads to a sugar crash and then you eat more to compensate, for several cycles, you could well end up eating more calories than in fat, if it keeps you feeling full. SinisterLefty (talk) 08:27, 1 November 2019 (UTC)[reply]

True, true. אילן שמעוני (talk) 08:59, 1 November 2019 (UTC)[reply]

November 1

Amateur solar telescopes

The common designs seem to focus on blocking most of the sunlight, so it isn't blindingly bright. But this seems to be a wasteful approach, to me. Most telescopes try to maximize light gathering power, but solar telescopes try to reduce it. Why not project the image onto a large enough area that it isn't blindingly bright, so as to not lose detail by filtering out light ? Wouldn't that make features like sunspots more visible ? Watching eclipses (partial or full) would be another application. SinisterLefty (talk) 06:30, 1 November 2019 (UTC)[reply]

Your suggestion only fits small-aperture telescopes, here's why: with a big telescope (my guess is that 200mm is too large) the heat that will be focused through the eyepiece will be enough to crack it, or even blow it to pieces.

I know for certain that with a 70mm aperture you suggestion is safe. I tried that. Directing the telescope to the sun was very frustrating, btw.

EDIT: I noticed your "so as to not lose detail". You do not lose detail if you make the holes in the opaque telescope cover at its opposite edges. The detail is determined by the effective aperture, and the effective aperture stays the same this way.אילן שמעוני (talk) 07:32, 1 November 2019 (UTC)[reply]

Not following your last comment. If only one photon comes from a particular feature on the Sun, that would have been collected by the telescope, and that photon is filtered out, then you lost that detail.

As for heat, here I would think filtering out the light would make things worse, if that filtered out light is turned into heat in the telescope. Rather than absorbing it, reflecting the excess light or refracting it, to a place designed to take the heat, would help. But if all the light passes through the lenses, very little should be turned into heat there. Keeping dust off the end of the eyepiece would be critical, though, as that would absorb light and heat up. SinisterLefty (talk) 15:42, 1 November 2019 (UTC)[reply]

The problem is the CONCENTRATION of heat in the eyepiece. The main mirror focus the heat from its entire area into a much smaller focal plain. Much like burning a paper with a magnifying glass - but with a larger scale. The cover you must use sits at the telescope front end, and so just gets warmed normally as if you laid the cover out in the sun. Only a tiny fraction of the radiation is allowed into the telescope itself.

As for your concern for image quality: Telescope angular resolution is proportional to its aperture. since the light from both holes focus to the same focal plain, it builds a single image - so you get the full width resolution.

I do not know of a specialized screening eyepiece except digital eyepieces, which are either low quality or VERY expensive (sometimes both). Projecting straight from the eyepiece is manageable enough, you just have to position the screen perpendicular to the common L shaped focuser. I am quite sure I'll find illustrations for this arrangement. אילן שמעוני (talk) 17:08, 1 November 2019 (UTC)[reply]

FOLLOW_UP: Is there equipment designed to project the telescope image onto a large screen ? I imagine you might need a long distance, without a special lens, to get the image to be large enough to not be blinding. Would the image also go out of focus over this distance ? SinisterLefty (talk) 16:03, 1 November 2019 (UTC)[reply]

The Helioscope has been around for quite a while. Jeremiah Horrocks used one for his observation of the 1639 transit of Venus and it was invented long before that. See also https://www.skyandtelescope.com/observing/observing-the-sun/Richerman (talk) 17:21, 1 November 2019 (UTC)[reply]

Take a peek at this short guide. Also, be aware that without very expansive H-Alpha filter you can not see solar eruptions. You can see granules as in the photo there, and sunspots - but, alas, there are currently no sunspots. אילן שמעוני (talk) 18:35, 1 November 2019 (UTC)[reply]

Distance between and position of objects in the galaxy

So, one thing I have noticed when reading about other stars and exoplanets is that we already have estimated distance from Earth for most of them in terms of parsecs and lightyears. Does this imply that their positions relative to Earth never significantly change as they orbit around the Milky Way galactic center and that the speeds in which they move is not really different from the speed of the solar system? Is it actually possible to draw a map of our galaxy with fixed position for every significant object inside it and use it as a long-term reference? 70.95.44.93 (talk) 09:17, 1 November 2019 (UTC)[reply]

No. While many stars do roughly move along around the galactic center, the variation is huge. For example μ Columba AE Auriga are moving very fast at a path unrelated to orbiting the center. I seem to recall an application or maybe a site that shows how the night sky will change in the future. Whithin 10,000 years the change is significant.

EDIT: Didn't find app, but found a relevant vid. אילן שמעוני (talk) 10:27, 1 November 2019 (UTC)[reply]

And it may seem like the objects in the sky are moving slowly, but keeping in mind that the distances are huge, maybe thousands, millions, or billions of light years, it takes a long time to move a significant portion of those huge distances, even at extremely high speeds. SinisterLefty (talk) 15:48, 1 November 2019 (UTC)[reply]

The answer is complicated because many Star systems are "binary"(2), "trinary"(3) or even hole "clusters" of suns (1000), sometimes assumed with a dominating Black hole or alike "monster"-object in their center, so the movement of individual suns in that system may change very dynamically over short time.

Also realize that this field of research has actually just started and demands very, very expensive tools and instruments. The James Webb Space Telescope will be launched next in March 2021 and NASA has projected the costs at roughly over 10 Billion $ then. Just for this single Telescope! --Kharon (talk) 22:22, 1 November 2019 (UTC)[reply]

Standing wave, not

See [8]. The article describes an actual standing wave, where two waves of the same period coming from opposite directions create a resultant wave that doesn't move horizontally, but changes greatly in magnitude, and features many equal peaks and troughs (see this video at 1:20: [9]). However, the pic at the top of the article is another phenomenon, where a wave doesn't change in either position or magnitude, and there is no interference between waves. This type generally has a large central peak/trough, with progressively smaller peaks and troughs following it, and seems to result from the geometry of the river bed just upstream. What is the real name for this phenomenon, and the physics behind it ? SinisterLefty (talk) 17:03, 1 November 2019 (UTC)[reply]

A Stationary hydraulic jump. Mikenorton (talk) 17:31, 1 November 2019 (UTC)[reply]

Thanks. SinisterLefty (talk) 18:32, 1 November 2019 (UTC)[reply]