a) Escape velocity earth: 11.2 km/s
b) earth orbit speed: 30km/s
c) incoming asteroids speed: what ever you want. If it is e.g. "your escape velocity" and it comes retrograde into the earth, then it is 41 km/s
Which is a different situation to RGB's:
escape speed IS EXACTLY the speed of an object with escape energy, and is in turn BY DEFINITION the speed of an object dropped from infinitely far away, initially at rest
Of course, if you complexify RGB's textbook situation by adding an initial velocity between the two objects - as you do, then you get the same answers.
Textbooks leave that out for the first exercise. You're on the second exercise.
Because absolute magnitudes can be measured as soon as an asteroid is found,
Weeeeellll... for certain values of "found", you could make that claim. If you've observed an object for long enough to work out it's orbit, and found a "pre-covery" image somewhere so that you've got the multiple-position data needed to calculate an orbit to MPC standards, then yes, you have the distance data needed to convert the apparent magnitude measured at your telescope into an absolute magnitude as it would have at a range of 1 AU. Of necessity, you also acquire knowledge of how far away the object is (you have calculated it's orbit). Calculating an orbit requires at least two direction measurements at different times (plus at least one distance measurement (via radar) or another direction measurement), which would rarely take less than 24 hours (two consecutive nights of observation).
while what an asteroid is made of, and what its color is, cannot.
However measuring it's colour (a hint to composition) and taking a reflection spectrum (a better hint to composition and classification) can theoretically take place in the first observation run (if your imager system can switch between imaging and spectroscopy without significant reconstruction).
how someone can be an avid-enough photographer to want to use pro equipment for photographing an eclipse, yet not avid enough to either already understand the need for a proper solar filter
Marvin put it very succinctly : "It gives me a headache to think down to that level."
Surprisingly, astronomers have been observing eclipses for over a century using all sorts of photographic equipment and some pretty big "light buckets". Generally, they (or the ones I've talked to, at least) buy sheets of filter material designed for the job, and make up a "big end" filter for each scope they intend to use. Next eclipse, if they're not using the 12in scope, but are using the more portable 8in scope, it's an easy task to make a 12in filter fit an 8in scope. Actually, it's not much harder to get an 8in filter to fit a 12in scope (think "lunar stop").
You buy the stuff once, and keep on using it until you see a pinhole in your pre-job equipment check. It's like - in the days of yore, you'd buy a bag of film holders and load them with your choice of film before the "big job". Then process the film, and re-load the holders for the next "big job". Or, since car analogies seem popular here, you buy a long-handled wheel nut wrench the first time you find that the piece of shit that the previous owner left in the car can't actually undo a wheel nut, then move it from car to car until it finally gives out.
I brought solar filter material for the 1999 eclipse, and keep it, it's mountings (some for cameras, some welder's goggles uprated to solar-capable, some sheet material taped onto an interchangeable filter square, and one "lunar stop" for a 150mm telescope, with solar filter film attached) and a roll of gaffer tape in a satchel that has got rolled out every eclipse since. Inspect before use (a pinhole might develop ; spiders like the bag in years it's not used) but otherwise observing and photographing an eclipse is neither dangerous nor difficult.
Staring into a solar eclipse is no more dangerous than staring into the sun when there's a quarter-Moon in the sky. Which is pretty dangerous. Glances into the sun - fractions of a second - aren't particularly dangerous, but that's not "staring". Of course, you don't get to actually see anything productive with a glance.
Put yourself into the bare feet of our ancestors yomping around on the savannah. One of them glances up at the sun in response to, say, the cry of a predatory bird. Eye full of sun ; looks away. This one is blinded to the level you indicate with a yellow arm band and three dots. Their neighbour and cousin who did exactly the same, but has either faster reactions or less sensitive eyes, looks away after the same amount of exposure and suffers no damage that lasts more than a minute or two. Which of the two leaves more descendants?
That is why occasional, intermittent looking into the Sun isn't a problem. Staring into the sun, overriding your instinct to look away, remains dangerous.
But we get this discussion every time there's a solar event. I just treat it as Darwin Award material. Blind yourself ; blind your children. It's better for the gene pool for you to get out sooner rather than later.
I thought Terry Pratchett was really into computers
Pratchett was a professional writer, having started as a journalist with ink, paper and shorthand, and worked his way through a gamut of technologies including using a nuclear power station to power his typewriter (CEGB, Hinckley point IIRC). He'd have used what worked well enough, and maybe had a different rig for computer games ("Only You Can Save Mankind") out of the office.
I suspect you're conflating Douglas Adams or Stephen Fry with Pterry. DNA and Fry certainly "gadgeted together", but Pterry wasn't really a metropolitan person, living 70-odd miles (and several darned peculiar furlongs) form the Great Wen.
Nevertheless, I would have liked to know what he was working on.
That may well still be on Rob's hard drive.
Quite likely, for things that were in the planning stages there were some discussions about [project name] with his publisher, collaborator, PA (Rob). Which are already covered by NDAs.
a detached garage. Since the bomb squad couldn't get to the dynamite, they set the garage on fire and let the whole thing burn to the ground.
Sounds like a correct action.
Contrary to what Hollywood will train people to think, most high explosives (and many low explosives) will burn perfectly unconcernedly if not confined. To get them to detonate, you need to apply a shock wave with a propagation speed of some thousand-plus metres per second. You don't get that accidentally - you need a specially designed detonator, containing small amounts of amuch more sensitive explosive.
Detached garage. Rebuilding cost a few thousands of pounds. Yeah - empty it of anything valuable not close to the "bang" then torch it. The cost of digging one small piece of debris out of a bomb-squaddy's face would be far higher.
If there had been detonators in the same stockpile... rather more iffy.
Upthread someone mentioned the nitroglycerine will explode if you bang it with a hammer. True. Which is why (get this - it's complex!) people aren't allowed to make or get hold of nitroglycerine without a triplicate shipload of paperwork. Nitrogen tri-iodide is even worse - that'll bang with the impact of a fly's foot. Which is why there is no commercial use for it, indeed, no use I'm aware of except making colourful bangs in the chemistry lab. When you make the stuff yourself.
The two main reasons that TNT is a popular explosive are (1) it's LOW sensitivity to shock in general (you need a powerful detonator) and (2) it's low sensitivity to shock when melted. The latter is a different point to the former - for all I know, frozen nitroglycerine could be safe to play squash with, but the liquid is a different matter. Most shell casings (such as the original subject) are machined in the casting and welding shop, cleaned of debris, then filled with molten TNT and thrown along the assembly line. Bang, clash, rattle! It's only when you put the detonator in that they need more than the respect any ton-plus moving object deserves.
The Hawaiians got to Hawaii about (IIRC) 500 CE, after several thousands of years of well-detailed expansion of the Polynesian peoples across the tropical Pacific from Taiwan/ Formosa. (Settlement of PNG was much, much earlier.)
The postulated "land bridge settlement" of North America took place ten thousand years earlier, across Arctic (not tropical) waters. I'd suggest you review your Arctic marine survival training course and compare it with your tropical training course if you can't remember the difference.
As it happens, there are plenty of people who consider an island-hopping settlement route to be perfectly feasible. The big problem is that the sea level then would have been 50 to 100m lower, putting their "hopping" settlements, encampments and even broken boats that far below sea level. Archaeological evidence is almost completely lacking. (The Channel Islands evidence someone mentioned is not incompatible with a settelment over a land bridge and through central Canada, BTW. Just pre-Clovis.) It's also almost completely lacking in the "ice free corridor" and Bering Straits, but where these are on land, archaeology is far cheaper than needing to use "technical" diving to search for it.
This is probably not the story you'd get from watching TV programmes. Because producers like neat, simple stories. With answers.
The sentence from the article which set off my "put this in the maybe column" reaction was this one "Only 1 to 2 percent of the collected DNA was human,"
This can probably be assigned to the actions of one or two (presently unidentified) people.
When the skeleton was discovered it was about 80% complete, including some lovely dense molar teeth in the skull. Between the discovery dive and the excavation dive programme (you need things like Teflon bags to avoid DNA contamination, and rigid boxes to protect the bones against impact with walls, floor or roof ; not part of a normal dive kit) someone (or sometwo ; I'd go for the two, despite the hazards associated) stole the skull and about 70% of the skeleton.
That might make you angry. It makes me absolutely fucking livid, because the person who did it was a skilled cave diver - a category I attempted to join but wasn't up to scratch.
I'm guessing the research was phrased more as "here's additional evidence against Clovis-first and for an earlier date" and the reporters added some sloppy wording around it to sensationalize things.
Why guess. Schwit1 provided a direct link to the paper. You can read it for yourself. In fact, this is the less interesting bit of what they say:
The oldest closed system U/Th age comes from around 21 mm above the pelvis defining the terminus ante quem for the pelvis to 11311±370 y BP. However, the skeleton might be considerable older, probably as old as 13 ky BP as indicated by the speleothem stable isotope data.
Which seems perfectly reasonable to me (I'm both a geologist and a caver. Allowing about 2kyr for 21mm of stalagmite growth is good for me. They have other isotope data to bolster this estimate, but I'm happy already.)
But that is not by any means the most interesting part of the abstract.
You mention that you like the coastal route prospect. So do I - have done for years. It's not credible to me that the people who populated the China-Korea-Russia-Kamchatka regions didn't do it without having at least fishing craft. And at that point, island-hopping along the Aleutians or across the Bering Strait becomes quite feasible (one summer, Ugh established a summer camp on that island on the horizon, and got good salmon. Next summer, Ugh, his brother and their wife started the camp earlier, stocked more, and over-wintered. Lather, rinse, repeat. Every so often, someone gets storm-blasted over the horizon, survives, lands to carry out repairs, then makes their way home ; an over-horizon link is made.) Once they get to the Alaska coast then essentially the same toolkit (material and behaviour) can carry them down the coast as fast as they want.
The big problem with such a scenario is that at say 20kyr ago, the sea level was 50+m lower than today, so any intermediate camps they made along the coast are now 50m below sealevel. Hard for archaeology. But not impossible.
Which is the interesting bit of the paper. The REALLY interesting bit.
Have you read the abstract yet? No, go on, I'm teasing you. You've got the link. Do it!
Here we use U-series techniques for dating a stalagmite overgrowing the pelvis of a human skeleton discovered in the submerged Chan Hol cave.
Get that? "submerged".
This skeleton was discovered by recreational cave divers, and came to the attention of researchers via social media posts showing a ~80% complete skeleton. (Props to the discoverers Valentina Cucchiara and Nick Poole (Liquid Jungle) and Thomas Spamberg for taking photographs not specimens.) Unfortunately between discovery and being able to organise a properly equipped excavation dive, someone robbed the site, stealing around 70% of the skeleton and leaving only small amounts (~10%) to work on. Since finger and fingertip bones were found, if it weren't for the robbery, there would be a hugely better dataset. Potentially even mDNA from within the teeth. Gone. Spilt milk.
The encouraging sign is that recreational divers in the area are very aware of the potential importance of these discoveries, and responsible enough to report them. That means that eventually we will start to find better data from the region. and that eventually should provide the data to clarify if the "coastal route" hypothesis is correct.
A complicating factor is that this discovery was made on the Caribbean coast of Mexico, in an area known for "blue hole" diving. That prospect isn't present on the Pacific coast. But eventually there will be exploration work on that coast too. Hell, if I could afford it, I'd be tempted to take my gags over for a bubble too.
But that East Coast location simply means that the arrival of humans on the west coast (or inland even) must have happened even earlier.
the Bering Sea, even in summer, is too far north to be survivable on a raft....
Do you have evidence to support this proposition? In particular, if your experimental set up starts with people who have spent their whole lives, for generations past, living in the glacial Siberian NE.
You might not be able to survive on a raft in the Bering sea tomorrow. That doesn't mean that its impossible, only that you don't know how to survive in Bering sea conditions.
Being unduly generous to the AC, she might be misremembering a speculation popular a few years ago which suggested that Neanderthal or early Cro-Magnons from the Lusitania/ Galicia/ Pays Basque/ Aquitaine / Brittany region could have possibly island- an iceberg hopped across the Atlantic by kayaking on fishing expeditions that went wrong. And that could have happened 20kyr ago. It's not impossible, but it is a big ask. And calling them "Vikings" is... peculiar.
The elements, and the wildlife. Which would be non-trivial accomplishments for your average lardball ultra-survivalist with a ton of hardware and no cellphone coverage, but is even more of an accomplishment for a man with a pair of hands and a brain.
Slashdot Mirror
You :
Which is a different situation to RGB's :
Of course, if you complexify RGB's textbook situation by adding an initial velocity between the two objects - as you do, then you get the same answers.
Textbooks leave that out for the first exercise. You're on the second exercise.
Weeeeellll ... for certain values of "found", you could make that claim. If you've observed an object for long enough to work out it's orbit, and found a "pre-covery" image somewhere so that you've got the multiple-position data needed to calculate an orbit to MPC standards, then yes, you have the distance data needed to convert the apparent magnitude measured at your telescope into an absolute magnitude as it would have at a range of 1 AU. Of necessity, you also acquire knowledge of how far away the object is (you have calculated it's orbit). Calculating an orbit requires at least two direction measurements at different times (plus at least one distance measurement (via radar) or another direction measurement), which would rarely take less than 24 hours (two consecutive nights of observation).
However measuring it's colour (a hint to composition) and taking a reflection spectrum (a better hint to composition and classification) can theoretically take place in the first observation run (if your imager system can switch between imaging and spectroscopy without significant reconstruction).
The guy was alive, noisily, when I left him pegged out face down for the ants.
Marvin put it very succinctly : "It gives me a headache to think down to that level."
You buy the stuff once, and keep on using it until you see a pinhole in your pre-job equipment check. It's like - in the days of yore, you'd buy a bag of film holders and load them with your choice of film before the "big job". Then process the film, and re-load the holders for the next "big job". Or, since car analogies seem popular here, you buy a long-handled wheel nut wrench the first time you find that the piece of shit that the previous owner left in the car can't actually undo a wheel nut, then move it from car to car until it finally gives out.
I brought solar filter material for the 1999 eclipse, and keep it, it's mountings (some for cameras, some welder's goggles uprated to solar-capable, some sheet material taped onto an interchangeable filter square, and one "lunar stop" for a 150mm telescope, with solar filter film attached) and a roll of gaffer tape in a satchel that has got rolled out every eclipse since. Inspect before use (a pinhole might develop ; spiders like the bag in years it's not used) but otherwise observing and photographing an eclipse is neither dangerous nor difficult.
Put yourself into the bare feet of our ancestors yomping around on the savannah. One of them glances up at the sun in response to, say, the cry of a predatory bird. Eye full of sun ; looks away. This one is blinded to the level you indicate with a yellow arm band and three dots. Their neighbour and cousin who did exactly the same, but has either faster reactions or less sensitive eyes, looks away after the same amount of exposure and suffers no damage that lasts more than a minute or two. Which of the two leaves more descendants?
That is why occasional, intermittent looking into the Sun isn't a problem. Staring into the sun, overriding your instinct to look away, remains dangerous.
But we get this discussion every time there's a solar event. I just treat it as Darwin Award material. Blind yourself ; blind your children. It's better for the gene pool for you to get out sooner rather than later.
Quite an old picture that. The text on the screen is a scene from "Dodger", published in 2012, dating this to 2011 at the latest.
Pratchett was a professional writer, having started as a journalist with ink, paper and shorthand, and worked his way through a gamut of technologies including using a nuclear power station to power his typewriter (CEGB, Hinckley point IIRC). He'd have used what worked well enough, and maybe had a different rig for computer games ("Only You Can Save Mankind") out of the office.
I suspect you're conflating Douglas Adams or Stephen Fry with Pterry. DNA and Fry certainly "gadgeted together", but Pterry wasn't really a metropolitan person, living 70-odd miles (and several darned peculiar furlongs) form the Great Wen.
All the more reason for his friends, colleagues and fans to welcome this fulfilment of his wishes.
Nice anecdote. Sounds very Heinlein.
That may well still be on Rob's hard drive.
Quite likely, for things that were in the planning stages there were some discussions about [project name] with his publisher, collaborator, PA (Rob). Which are already covered by NDAs.
But he wasn't American, and was very glad of it.
Given Pterry's memory and ... thingumy .. problems, that's not really funny
(I know - without heating it above the Curie temperature of the magnetic medium. Or decomposition of the binder holding the medium in place.)
Sounds like a correct action.
Contrary to what Hollywood will train people to think, most high explosives (and many low explosives) will burn perfectly unconcernedly if not confined. To get them to detonate, you need to apply a shock wave with a propagation speed of some thousand-plus metres per second. You don't get that accidentally - you need a specially designed detonator, containing small amounts of amuch more sensitive explosive.
Detached garage. Rebuilding cost a few thousands of pounds. Yeah - empty it of anything valuable not close to the "bang" then torch it. The cost of digging one small piece of debris out of a bomb-squaddy's face would be far higher.
If there had been detonators in the same stockpile ... rather more iffy.
Upthread someone mentioned the nitroglycerine will explode if you bang it with a hammer. True. Which is why (get this - it's complex!) people aren't allowed to make or get hold of nitroglycerine without a triplicate shipload of paperwork. Nitrogen tri-iodide is even worse - that'll bang with the impact of a fly's foot. Which is why there is no commercial use for it, indeed, no use I'm aware of except making colourful bangs in the chemistry lab. When you make the stuff yourself.
The two main reasons that TNT is a popular explosive are (1) it's LOW sensitivity to shock in general (you need a powerful detonator) and (2) it's low sensitivity to shock when melted.
The latter is a different point to the former - for all I know, frozen nitroglycerine could be safe to play squash with, but the liquid is a different matter. Most shell casings (such as the original subject) are machined in the casting and welding shop, cleaned of debris, then filled with molten TNT and thrown along the assembly line. Bang, clash, rattle! It's only when you put the detonator in that they need more than the respect any ton-plus moving object deserves.
The postulated "land bridge settlement" of North America took place ten thousand years earlier, across Arctic (not tropical) waters. I'd suggest you review your Arctic marine survival training course and compare it with your tropical training course if you can't remember the difference.
As it happens, there are plenty of people who consider an island-hopping settlement route to be perfectly feasible. The big problem is that the sea level then would have been 50 to 100m lower, putting their "hopping" settlements, encampments and even broken boats that far below sea level. Archaeological evidence is almost completely lacking. (The Channel Islands evidence someone mentioned is not incompatible with a settelment over a land bridge and through central Canada, BTW. Just pre-Clovis.) It's also almost completely lacking in the "ice free corridor" and Bering Straits, but where these are on land, archaeology is far cheaper than needing to use "technical" diving to search for it.
This is probably not the story you'd get from watching TV programmes. Because producers like neat, simple stories. With answers.
You would do. However, the actual data clearly shows that the stalagmite was formed after skeletalisation of the pelvis.
This can probably be assigned to the actions of one or two (presently unidentified) people.
When the skeleton was discovered it was about 80% complete, including some lovely dense molar teeth in the skull. Between the discovery dive and the excavation dive programme (you need things like Teflon bags to avoid DNA contamination, and rigid boxes to protect the bones against impact with walls, floor or roof ; not part of a normal dive kit) someone (or sometwo ; I'd go for the two, despite the hazards associated) stole the skull and about 70% of the skeleton.
That might make you angry. It makes me absolutely fucking livid, because the person who did it was a skilled cave diver - a category I attempted to join but wasn't up to scratch.
The limit for recovery of sequenceable DNA is around 400kyr - from a horse(-ish), IIRC.
Why guess. Schwit1 provided a direct link to the paper. You can read it for yourself. In fact, this is the less interesting bit of what they say :
Which seems perfectly reasonable to me (I'm both a geologist and a caver. Allowing about 2kyr for 21mm of stalagmite growth is good for me. They have other isotope data to bolster this estimate, but I'm happy already.)
But that is not by any means the most interesting part of the abstract.
You mention that you like the coastal route prospect. So do I - have done for years. It's not credible to me that the people who populated the China-Korea-Russia-Kamchatka regions didn't do it without having at least fishing craft. And at that point, island-hopping along the Aleutians or across the Bering Strait becomes quite feasible (one summer, Ugh established a summer camp on that island on the horizon, and got good salmon. Next summer, Ugh, his brother and their wife started the camp earlier, stocked more, and over-wintered. Lather, rinse, repeat. Every so often, someone gets storm-blasted over the horizon, survives, lands to carry out repairs, then makes their way home ; an over-horizon link is made.) Once they get to the Alaska coast then essentially the same toolkit (material and behaviour) can carry them down the coast as fast as they want.
The big problem with such a scenario is that at say 20kyr ago, the sea level was 50+m lower than today, so any intermediate camps they made along the coast are now 50m below sealevel. Hard for archaeology. But not impossible.
Which is the interesting bit of the paper. The REALLY interesting bit.
Have you read the abstract yet? No, go on, I'm teasing you. You've got the link. Do it!
Get that? "submerged".
This skeleton was discovered by recreational cave divers, and came to the attention of researchers via social media posts showing a ~80% complete skeleton. (Props to the discoverers Valentina Cucchiara and Nick Poole (Liquid Jungle) and Thomas Spamberg for taking photographs not specimens.) Unfortunately between discovery and being able to organise a properly equipped excavation dive, someone robbed the site, stealing around 70% of the skeleton and leaving only small amounts (~10%) to work on. Since finger and fingertip bones were found, if it weren't for the robbery, there would be a hugely better dataset. Potentially even mDNA from within the teeth. Gone. Spilt milk.
The encouraging sign is that recreational divers in the area are very aware of the potential importance of these discoveries, and responsible enough to report them. That means that eventually we will start to find better data from the region. and that eventually should provide the data to clarify if the "coastal route" hypothesis is correct.
A complicating factor is that this discovery was made on the Caribbean coast of Mexico, in an area known for "blue hole" diving. That prospect isn't present on the Pacific coast. But eventually there will be exploration work on that coast too. Hell, if I could afford it, I'd be tempted to take my gags over for a bubble too.
But that East Coast location simply means that the arrival of humans on the west coast (or inland even) must have happened even earlier.
Do you have evidence to support this proposition? In particular, if your experimental set up starts with people who have spent their whole lives, for generations past, living in the glacial Siberian NE.
You might not be able to survive on a raft in the Bering sea tomorrow. That doesn't mean that its impossible, only that you don't know how to survive in Bering sea conditions.
Hydrothermal springs, if you ask me. Damn these eukaryotes and their choking oxygenic toxic waste !
Being unduly generous to the AC, she might be misremembering a speculation popular a few years ago which suggested that Neanderthal or early Cro-Magnons from the Lusitania/ Galicia/ Pays Basque/ Aquitaine / Brittany region could have possibly island- an iceberg hopped across the Atlantic by kayaking on fishing expeditions that went wrong. And that could have happened 20kyr ago. It's not impossible, but it is a big ask. And calling them "Vikings" is ... peculiar.
The elements, and the wildlife. Which would be non-trivial accomplishments for your average lardball ultra-survivalist with a ton of hardware and no cellphone coverage, but is even more of an accomplishment for a man with a pair of hands and a brain.