Green Baron

Wow ! Thanks guys ! 2203 ! @Gargamel gap 24

2143

They are the main navigational instrument at least on manually piloted sailing ships when underway. Especially during night or on the open ocean when there is no other reference the compass is the helmsman's best friend and always in sight. If a gps is on board (mostly the case today), it'll be counter checked several times a day for positioning, but not for steering a course. It is simple: the compass reacts directly to changes, while the gps needs some time. Steering after the gps leads to a curve like a drunkard's walk (chasing the needle) and therefore chaos when among other traffic. Don't do it ;-) A gps has its strength together with an autopilot, though a magnetic compass (fluxgate for signal transmission) will back up the automatic rudder.

A correction for transforming magnetic course to true course must always be applied. So things will not change on that end, the corrections will just become bigger (could be >180° actually, or a sign flip). In navigation, one can always use the stars, provided one has an exact chronometer (aka clock). Those who can operate a sextant will be unimpressed. The rest of us will have to check the display every now and then.

Yes, that would be the flip mentioned above. Nobody knows for sure how in detail a polarity flip of the earth's magnetic field occurs. We don't even know how long it takes, maybe 100s of years ? Pretty fast ;-). But there are no remarkable extinctions connected to past flips. So, probably, maybe, it just flips. No refund on old compasses ... Geomagnetism is used as a method of dating because the phases are preserved in ocean floor when it solidifies. So, from the mid ocean ridges to the continents the polarity is recorded, plus a few ophiolites (ripped off ocean crust during subduction, stacked in between continental crust, example Omani mountains), reaches back a few (not many) hundred million years. Lave flows can be dated as well this way, which helps for example in East Africa with the dating of early human tools and so. Actually, the Gauss-Matuyama transition was the marker for identifying the earliest human tools for quite some time. But they can do better these days ;-)

Well, currents in the core build the magnetic field. But we can't take a look, so we must find a best fitting (and constantly changing) model. It'll all be easier in the future, when the earth has cooled enough so that all these combobulations have come to a rest. That i can say with some confidence :-)

It is probably not like the poles wander around the globe when they switch, that would mean too huge changes in mass movement in the core. There may be short periods with a very weak or even without a magnetic field and/or with high local variations until it builds up again. But nothing is clear, afaik.

Judging from the frequency it gets referenced here, The Core must be be a fascinating movie ... Seriously, yes, a model update is necessary. And this has quite practical consequences too, like nautical charts. I recall speculations in the late 1900s/early 2000s that a pole flip could be standing before us, but i haven't heard of that since a long time. Maybe the idea was abandoned because too much speculation. In general approximation, it is a dipole. In practice, adjustments are necessary and pole wandering is independent. Which is the case right now. It may happen that locally a compass may not point to one of the "main" poles, non-dipole variations may create a local north or south pole (suggesting a movie "The Quadrupole" ). Anyway: a model of earth's magnetic field is only valid for a limited time.

2113 It is getting tedious to find images ...

I was just too lazy to search for the paragraphs in the regulations :-)

Yes, on a commercial flight, the crew can refuse to let any passenger on board or even have them leave the plane if they think they are a potential risk for the flight. This is the crews responsibility to guarantee safety. They will even land out of schedule and have an unruly passenger guided out by security. Plus there are other nasty side effects like being charged for the extra cost and so on. It happens from time to time, after football matches or on the flight home from certain cheap mass tourism places etc. ... Better stay with tomato juice and tabasco until the flight is over ;-)

Jethro Tull, 1977. Just beautiful rock music.

2099

2081

Thanks ! Interesting that somebody considers a failed supernova of a blue supergiant as being less improbable than a tidal disruption, which there is another examples of (Arp299). The discussion is on ...

We didn't have this for quite some time, couldn't get it out of my head this afternoon: (Can't find the original video, sorry ...)

2063

“Bringing deep space capabilities into the ConsenSys ecosystem reflects our belief in the potential for Ethereum to help humanity craft new societal rule systems through automated trust and guaranteed execution,” said Lubin. I see, says i. Mr. Crusher, set a course ! Engage ! :-) Edit: I mean, was asteroid mining ever really in "danger" of becoming a bubble at all ? There is nothing more than more or less realistic proposals of going there and doing what with unclear resources.

Even if you accept that as being set in stone (which many don't out of their understanding of how evolution works), dates in lice studies are spread between 75,000 and 540,000 before now. Parasites actually do jump from different hosts. Example the bed louse, which apparently seemingly came over from cave bats.

This is not as much scifi as one might think: link

2017 (who remembers the solar eclipse ?)

Well, assuming that there actually is a co-evolution between lice and clothing, which is debatable, lice can have evolved elsewhere and then chosen the new host, or they can have evolved on the new host but much later. And, where things are even more debatable, if not shaky, that a certain mutation rate over a long period is maintained. Which is needed to estimate the moment of speciation in the past. The rest is statistics. The argument can contribute to the discussion, but it is less than secure. ------------- Composite tool making (wood hafting, birch tar, stone) and traces of tannic acids in the last warm phase: https://www.sciencedirect.com/science/article/pii/S1040618213004084 A nearby find site is 70.000 years older (Neumark Nord 2), and thus dates to the beginning of mis 6/end of mis 7(*), but does not show the same technological level. Future will tell moar :-) (*) climatic stages in the pleistocene, measured by stable oxygen isotope ratios from foraminifera, numbered from today on backwards. pair=cold/impair=warm. They roughly coincide with milankovic cycles of 40/100,000 years. Just to not loose the space connection totally :-)

I am just conservative to avoid discussion :-). Another study on the same subject says 540,000. The reason to say 200,000: Ante-Neandertals in central Europe (and possibly in Siberia but until now without direct finding) during OIS-6 (pre OIS-5) could not have survived without effective protection. ----------- Side note, and the reason to say "at least": Some anthropologists conclude that some form of protection must have been available even for the Homo erectus when they left Africa towards Europe and Asia, like Dmanisi. Since there is some evidence that one individual was probably taken care of by the group (no teeth), the survival of these in that time and climate is not guaranteed by adaptation alone. So, maybe, much earlier, like 1.8 million years ? But that is speculative, and surely the upper limit.

:-) 1997

I hope it gets better once we are out of the years with all those silly cars :-) Until then: