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# GeeKay

Senior Members

118

1. ## Help needed over a "three body" orbital calculator

It's okay. I have it now. . . it's the 'Hill Sphere" set of calculations I was seeking. Phew. . . https://en.wikipedia.org/wiki/Hill_sphere
2. ## Help needed over a "three body" orbital calculator

I used to have an excellent online calculator that enabled me to show the possible orbits of a satellite around a larger secondary body (e.g. a moon) which itself was in orbit around (say) a planet. Unfortunately my local PC repair shop unwittingly deleted the calculator during a refurb. And since I can't recall the scientific/technical term for this "three-body" gravitational arrangement, I'm no longer able to locate online the calculator in question. I would therefore be very grateful if anyone can help me here. PS. Unhappily I don't have anything like the mathematical skillset to do these calculations by hand. Thanks in advance.
3. ## What is the Opposite of Superposition?

Yes, I think I begin to get it now. Thanks, studiot, for your detailed and helpful explanations. Food for thought, indeed. G
4. ## What is the Opposite of Superposition?

It could be that the use of the adjectival 'super' in superposition has been confusing me. If measurement is the key that defines whether a quantum system is in superposition or not, then what about measured versus unmeasured? Personally I suspect the opposite of Spain is located somewhere in the South Pacific. . .
5. ## What is the Opposite of Superposition?

A few years ago one of my nieces, then aged twelve, asked me what "the opposite of superposition" is. Her question completely stumped me at the time. It still does. I have since considered placeholder answers like: normal position, position, classical position, etc. None of them seem satisfactory, however. This same question (with full quotation marks) also continues to stump Google. NB. I am prepared to be told that the question is nonsensical - that it'll be like asking what the opposite of Spain is, for example. Still, I'm up for it.
6. ## Dry air and respiratory issues

Regarding ventilation: this used to be potentially an issue given the room's double glazing. It was necessary to block off the window's trickle vent, this due to the wind persistently recreating Bob Dylan-like harmonica sound-effects with it (worse still, given the prevailing wind direction in this part of the world, the house itself is situated near the top of a south-west facing hill with an uninterrupted view of the horizon). The room isn't particularly dusty, although I will now give it an early spring clean. Allergens remain an unknown at present. On the other hand, I do keep the door open at all times, beyond which is a landing which in turn leads to the stairwell. Meanwhile, the ambient humidity level outside the house is 91% at the time of writing, while the temperature is just 2 degrees Celsius. This high humidity count is actually fairly typical in this part of England. What is confusing, though, is the relationship between temperature and humidity. Do people living on the equator who routinely endure both high temperatures and (say) 100% humidity levels suffer from respiratory problems? Or have they adapted to these conditions in the same way that people living at high altitudes have adapted to low oxygen levels due to the thinness of the atmosphere? Extremely puzzling, that. studiot, I note with interest your own high humidity readout. To reiterate: in respiratory terms I really do feel better for having a count of between 65% ~ 70%. I just wish I knew why.
7. ## Dry air and respiratory issues

This is from a person who spends several hours a day word-processing in a smallish upstairs boxroom (2.4m x 3.8m) that faces south-west. The room is centrally heated (20 C) and efficiently double-glazed. For sometime now I have suffered from minor, but persistent respiratory problems, stuffy nose, throat-clearing issues. I also have chronic sinusitis, which I plan to do something about just as soon as Covid-19 finally abates. . . whenever that might be? Meanwhile, these respiratory problems have all but vanished since using a humidifier. It seems that it more than compensates for the room's dryness, which may be due in large part to running two PCs, plus a UPS battery system and other electronics. What is puzzling, though, is that the full benefits only arise when the room's humidity levels hover around the 70% mark. This must be mentioned because it's routinely cited that optimum humidity levels should be between 30% ~ 50%. This is waaay too low for me, which means either I'm an exception (i.e. a naturally 'wet' person) or else I'm failing to understand something fundamental about humidity. Any comments/suggestions welcomed. Apologies for the repeated usage of the first person singular. Unfortunately the issues related above apply particularly to the poster.
8. ## Responding to 5G Conspiracy Fears

It should bother you - if only because the "wilfully ignorant" tend to vote into office the kind of dickheads who are currently doing the rest of us NO favours whatsoever. Anyone care for a re-run of 2017? Then there's this. . . https://www.nytimes.com/2019/12/28/climate/trump-administration-war-on-science.html
9. ## Responding to 5G Conspiracy Fears

This is a valid point. . . as far as it goes. It's just that it's not enough any longer. In the age of the internet it's no longer a matter of leading a person to a book; rather it's a case of leading the book to the person.
10. ## Responding to 5G Conspiracy Fears

Many thanks for the link. Yes, the fact that both are just opinion pieces illustrates how so-called "truthers" like Mark Steele can patrol their chosen agendas the way they do. This is more an internet problem than a purely science-based one. Still, speaking as a layperson/armchair observer here, it might be helpful if scientists took on Steele and his ilk more directly. There's no chance of getting such folk (and the majority of their camp followers) to alter their views by reasoned debate, of course - not when these views are buttressed by emotional convictions. All the same it would surely help the many undecided, even the merely disinterested. Just an observation.
11. ## Responding to 5G Conspiracy Fears

Is there any truth in the proposition that 5G is harmful to health? Many thanks. https://blogs.scientificamerican.com/observations/we-have-no-reason-to-believe-5g-is-safe/#
12. ## Help Needed Over Stellar Magnitude Issue

swansont - many thanks for your succinct answer to what has been a long-term headache for me. Much appreciated!
13. ## Help Needed Over Stellar Magnitude Issue

I am tying up the loose ends of a SF short story I wrote last year, featuring a neutron star. Right now, though, I'm stuck over a long-term problem concerning the star's luminosity. It's surface temperature is 8,200 K and has a diameter of 20 kms. My problem has consisted of trying (and failing) to calculate what the star's absolute magnitude would be. I'm afraid this is beyond my abilities to solve, and unfortunately I don't know anyone among my friends who has the mathematical nous to help me out here. So I would be extremely appreciative if someone here could put me out of my misery. Many Thanks!
14. ## Fast Rotating Asteroids

What would be the theoretical maximum spin-rate of a small asteroid (25 - 100m diameter?) if it were, for example, composed of a single 'monolithic' chunk of iron? This question arose after reading up on the subject in a Wikipedia article. Listed in it is one such asteroid with a spin-rate of around 30 seconds. Could this be bettered, given the above parameters? Many thanks. https://en.wikipedia.org/wiki/List_of_fast_rotators_(minor_planets)
15. ## Braking using Escape Velocity

Yes, I understand now. In other words the only 'practical' way for an object to decelerate while passing through an intense gravitational field would depend on powered means, not inertial. Moreover, the fact that the incoming object is moving at 0.01c relative to a given mass would (I should imagine) rule out all variations of power assist - this insofar that the proper velocities of nearly all stars aren't remotely relativistic, that's to say within local frames. Many thanks for clearing up this matter for me.
16. ## Braking using Escape Velocity

I'm wondering if it's possible to use the gravitational field of a massive object to decelerate a spacecraft moving at high velocity. An example is this: if a spacecraft moving purely on inertia at one percent light-speed performed a flyby of a one sol mass neutron star (or black hole) at a given altitude, would the gravity field cause the spacecraft to swing round the star, slow it up or else deflect its trajectory in a meaningful way? According to one online calculator the escape velocity of a solar mass neutron star at a distance of 25,000 km equals 3,000 km/s or 0.01 c. At this distance the tidal pull exerted by the star's gravity would be minimal, therefore represent no hazard to the ship or its crew. That said, I'm curious to know what would be the outcome. PS. It's the escape velocity I'm interested in: not the star's proper motion as a means of affecting a change in delta-v. Many thanks.
17. ## Blu-ray Audio Issues - A three-pipe problem?

Hi Yes, I'm looking forward to trying out these ideas once I get the offending discs back from a friend of mine whose been investigating the problem. I'll start with Phil for All's solution - this being a likely cause, given my tendency to fumble around with the player remote when watching films in subdued lighting. Failing that, I'll attempt to change the movie's audio setup in the discs' formating options (thanks, Memammal) and see what happens. Again, thanks for all the helpful advice - I've learnt a great deal from it
18. ## Blu-ray Audio Issues - A three-pipe problem?

Certainly seems to be. One question, though: how come the the discs and/or the player have started playing up like this? I say this because they always played okay in the past, using the existing player. It's only now I've started having this problem here. Thanks for getting back to me, by the way.
19. ## Blu-ray Audio Issues - A three-pipe problem?

I'm afraid I don't - the only Blu-ray player I have is the one I use for the TV (both my PCs are DVD-only). However, a friend of mine reports that the discs play fine on his own Blu-ray player. So it seems the source of the problem lies with my player. Yet it has no troubles playing my other Blu-ray films. That's what's bugging me, perhaps more than anything else.
20. ## Blu-ray Audio Issues - A three-pipe problem?

A strange conundrum: nowadays whenever I try to play my Blu-ray edition of 'The Lord of the Rings', I get plenty of video, but no audio. That's to say there's audio throughout the preamble (adverts etc) that comes before the main feature starts. But as soon as the actual cinematic part of the disc begins it goes completely silent. The same problem exists on all three discs - though, interestingly enough, it doesn't occur on any of the special features discs bundled with the boxed edition. They come out loud and clear! No other Blu-ray film or DVD of mine has this weird and wonderful audio issue. They play just fine. It occurs only on the three LOTRs discs - and then it's just the cinematic sections. I haven't loaned the box set to anyone. The problem seems to have manifested entirely by itself. NB. I must confess to having hawked this problem around various online help forums, and so far I've received zilch responses. So this is my last port of call. As for myself, things have reached the point whereby I simply want to know what the cause is, even if nothing can be done about it. There has to be a rational scientific/technological explanation, one that ultimately makes sense. Otherwise I might as well start believing in fairies. . . perhaps even in the existence of Middle Earth? Many thanks.
21. ## Martian Aurora: to see or not to see?

I gather that Mars regularly experiences aurorae, this despite the planet's lack of a global magnetic field. It's also stated that these aurorae occur in the ultraviolet wavebands. I assume from this that these displays are invisible to the human eye. This being so, I'm intrigued to come across artistic interpretations on the net that suggest how "auroras will look on certain parts of Mars" (to quote the text accompanying one such image). Does this mean that aurorae are actually visible, after all? Or am I missing something here?
22. ## Neutrino Query

Ah, yes, I understand now. Thanks for pointing this out to me. I had intended to use the image of an incoming comet and a rogue minor planet (of Ceres mass) passing through the solar system as an analogy for the expansiveness of sub-atomic space. But I can see now that this is no analogy at all. PS. Those cloud chamber shots are astonishing!
23. ## Neutrino Query

Yes, I should have used 'concentration' rather than 'density'. I stand corrected. So I guess then that if 1 cm2 of skin contains (in round figures) a quadrillion atoms, this means that there's an excess of around 15,000 more atoms than those neutrinos passing through this same area per second. But as Janus points out, a given 'atom' consists mostly of space, which explains why the strike rate is so low. (At some point I'm going to sit down and calculate exactly what this means at a sub-atomic level). Still, I'm intrigued as to why there appears to be such a glaring contrast between the strike rates of neutrinos and (say) cosmic rays. Yes, I surmise that neutrinos are chargeless and nearly massless particles, while cosmic rays, which being composed mostly of high-energy protons, are both enormously more more massive and carry a charge. Yet if atoms are comprised largely of emptiness, I'm left wondering why cosmic ray nuclei are many times more damaging in a biological context. Or am I missing out on something here?
24. ## Neutrino Query

I understand that around 65 billion neutrinos pass through every square centimetre of human skin (or any other skin for that matter) per second. I also gather that a human being can expect to be struck by an individual neutrino perhaps once or twice in a lifetime. These statistics, if true, are remarkable on several counts. Nevertheless, in order to get an handle on what this continual neutrino blitztkrieg really means at an atomic level, I've been trying to find out what the average density of atoms there are in a given square (not cubic) centimetre of human skin - but no luck so far. Does anyone have even an approximate answer to this admittedly obscure question? Many thanks.
25. ## The Ratio of a Radius?

Thanks for unsticking my brain - and to ajb for supplying the correct formula. Just one other point - well, two actually: I assume that kilometers and kilos respectively should be used as a metric when applying the above formula to a given celestial body. The second point is rather more complicated: how does one use the formula's solution as a means of calculating a celestial's body's focal sphere? As examples, a minimum of 550 AU is cited for the Sun, 15,300 AU for the Earth, and a focal sphere of just 10 million km for Sirius B, but I don't know how these figures are derived. (I'm afraid I only have an antique GCSE in Maths to assist me here). Many thanks. http://www.centauri-dreams.org/?p=35498 Correction: I meant 'focal distance' not 'focal sphere.'
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