Science desk
< July 27	<< Jun | July | Aug >>	July 29 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

July 28

Have any studies examined how awareness of one's own ecological footprint impacts self-esteem? I doubt I'm the only one who's ever wondered how many tons of carbon dioxide I'm worth to the rest of humanity. NeonMerlin 02:41, 28 July 2014 (UTC)[reply]

Not that I'm aware of, though the negative ecological footprint of a single person is approximately zero. You're much more likely to affect the rest of humanity with communicable diseases than anything to do with carbon. I'd be more worried about your anti-biotic footprint if it makes you feel better. Plus your footprint is all within your control with use of fossil fuels. I'd question you're awareness if it was affecting you self-esteem, mot the other way around. --DHeyward (talk) 09:12, 28 July 2014 (UTC)[reply]

DHeyward, do you mean the ecological footprint per capita in total, or just at the margin (which would imply an increasing return on carrying capacity from carbon sinks)? NeonMerlin 17:02, 29 July 2014 (UTC)[reply]

Well, let's think of a few examples, people who fly all over the world to lecture us about how we shouldn't be flying all over the world. Al Gore, Tim Flannery,Michael Mann for example. If one were to try and limit one's CO2 output to the average worldwide number , you'd be allowed the energy intensity per capita of Cuba, for example. Greglocock (talk) 10:35, 28 July 2014 (UTC)[reply]

And everyone in Cuba is happy ("or else"). ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:16, 28 July 2014 (UTC)[reply]

People who care about their carbon footprint probably try to minimize it, and thus feel good about themselves, while those who don't care are unaffected. However, there may be some who care about it and feel depressed no matter what, as they can never get their carbon footprint low enough to be happy. StuRat (talk) 14:45, 28 July 2014 (UTC)[reply]

Some folks aren't happy unless they aren't happy. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:16, 28 July 2014 (UTC)[reply]

Debbie Downer ? StuRat (talk) 17:40, 28 July 2014 (UTC) [reply]

Yep. Where is she now? Working for Fox News, maybe? ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:45, 28 July 2014 (UTC)[reply]

You obviously don't watch Fox or only watch Judge Jeannine, Bugs. Harris Faulkner and Megyn Kelly (!) ? Unfortunately, not only is a certain person I won't name an angry drunk, Mom's also never happy unless she's unhappy. I've advocated a carbon tax in the form of a tax on fuel and packaging an other inefficiencies for years. The problem is while you could easily get most Americans to agree to a large tax on shipping and packaging costs in exchange for an end to sales taxes, the left wants to keep the latter on top of the former. μηδείς (talk) 21:47, 28 July 2014 (UTC)[reply]

I should have put that one in small print. And I know who you're talking about. He's on leave, so to speak. As regards taxes, I'm like any American, in that I strongly support taxes on things I don't use. And as regards a carbon tax, you'll never get conventional industry to accept it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:00, 28 July 2014 (UTC)[reply]

We have just the reverse issue here in Michigan, where the right wants to repeal a business tax. They argue that this tax is unfair, since businesses not only have to pay sales tax when they buy equipment, but must pay tax on it every year after, too. That would be a reasonable argument, iff they would increase another business tax to make the bill revenue-neutral. But, of course, they made no such proposal.

As for a tax on packaging, that might have some other benefits, like reducing the amount of garbage overfilling our landfills. A deposit is another approach. The 10 cent Michigan bottle deposit on carbonated beverage containers has worked wonders to clear the sides of roads of returnable bottles, as homeless people will collect them if anybody tosses them out there. Nonreturnable bottles and other packaging continue to lead to littering and illegal dumping, though. For example, some kindly individual was nice enough to donate a vodka bottle to us last week by leaving it for us on our front lawn. I accepted his generosity, rinsed out the bottle, and put some flowers in it. StuRat (talk) 12:07, 29 July 2014 (UTC) [reply]

If we put a printed newspaper outside, could satellite capture a picture of that newspaper with readable text?--115.73.31.225 (talk) 10:46, 28 July 2014 (UTC)[reply]

Well, see Satellite imagery#Resolution and data. For current commercial satellites the answer is certainly not. The maximum resolution available from spy satellites is not something that countries publicize, but is unlikely to be that good because of having to look having to look through the atmosphere. --50.100.189.29 (talk) 12:12, 28 July 2014 (UTC)[reply]

Imagery intelligence#Satellite discusses the Rayleigh criterion limit for resolution, and says that IMINT satellites are believed to have a resolution of about 10cm. So the answer appears to be "no" even with spy satellites. Red Act (talk) 13:41, 28 July 2014 (UTC)[reply]

The US military has been filled with stories of satellites with ungodly resolution. One frequent claim is that they can read car license plates from orbit - another is that newspaper headlines can be read from orbit. Both of those claims were made during the cold-war era when the actual photographs were conveniently labelled "Top Secret" and nobody could be called upon to prove this capability. Probably those are both apocryphal. The US Military certainly do have 10cm imagery, I've worked with it - it's not even secret...but that's not enough to do either of those things. An entire newspaper would be only a handful of pixels and you'd be lucky to tell whether a car even has a licence plate - let alone be able to read it!

The highest resolution Google Maps images are also around 10cm - but they mostly use aircraft-derived photography.

Right now, the US Department of Commerce places a ban on commercial satellite photography with resolutions under 50cm - on grounds that this is the highest resolution that doesn't allow you to see individual humans - hence preserving some sort of anonymity. That limit is currently being appealed by at least one commercial provider (DigitalGlobe) [1] who could provide 40cm resolution with satellites already in orbit - and who plan to launch new satellites with 25cm capability sometime next month! The US Military and the Whitehouse have already lifted their versions of the resolution cap - and it seems that the Department of Commerce may finally eliminate all restrictions sometime this year. Some people are horrified by the privacy implications - but since Google Maps already provides higher resolution than that from manned airborne photography, and the un-banning the use of commercial drone aircraft is probably going to happen just as soon as the FAA can figure out the flight rules for such craft - it seems pointless to disallow satellites from doing the same exact thing.

But no, I don't think reading the text on a newspaper from orbit is possible right now...maybe not ever. That said, I would imagine that even with 10cm imagery - you could get a good enough image of the page to recognize which newspaper it is, and infer which page was being looked at by comparing the blurry image you got from orbit to images of all of the pages of all of the newspapers printed in that part of the world within a week or so of the date that the photograph was taken. In a sense, perhaps that's good enough.

SteveBaker (talk) 14:19, 28 July 2014 (UTC)[reply]

Is that 10 cm limit just for visible light ? How about if we move to the non-visible parts of the spectrum ? StuRat (talk) 14:52, 28 July 2014 (UTC)[reply]

Those are either outside the Optical window or longer, hence worse. Jim.henderson (talk) 16:26, 28 July 2014 (UTC)[reply]

In addition to Earth's atmosphere blocking above-visible-light frequencies, the solar spectrum cuts off quickly below violet. Unless we posit a giant orbiting ultraviolet flash bulb, it would be photographing in the dark through an opaque wall. 88.112.50.121 (talk) 19:14, 28 July 2014 (UTC)[reply]

Thank you all for very detailed responses. I have one more question. I watched an American movie describing an American POW who notifies his superiors his location by facing the sky (to let a satellite see him). In real life, is this possible to identify a man through satellite if he faces the sky?--115.73.31.225 (talk) 16:57, 28 July 2014 (UTC)[reply]

Based on the resolution described above, no. I think a better method is to spell something out on the ground. If spread over a large enough area, it won't be noticeable from the ground. StuRat (talk) 17:22, 28 July 2014 (UTC)[reply]

• This comment reminds me of a science-fiction short story by Timothy Zahn. Unfortunately, by mentioning it in this context I have revealed the ending, so if I reveal the title as well, it becomes a spoiler. Follow this link if you would like the story identified anyway. --50.100.189.29 (talk) 22:28, 28 July 2014 (UTC)[reply]

There's a new film called Lucy, based on the debunked notion that we only use 10 percent of our brains. The notion of being facially identified by a satellite was also used in a movie starring Gene Hackman and Will Smith, I forget the title. Basic preposterousness never stops writers from writing. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:31, 28 July 2014 (UTC)[reply]

Enemy of the State, incidentally. Tevildo (talk) 18:16, 28 July 2014 (UTC)[reply]

Somewhere in the attic is my college physics text, which if I recall correctly, had a way of calculating the maximum resolution based on aperture size, and i recall calculating long ago that a spy satellite would have to have unrealistically huge optics to allow reading wristwatches, newspaper headlines, or even license plates. This is a limit regardless of atmospheric effects or the quality of the lenses or sensors. Edison (talk) 19:44, 28 July 2014 (UTC)[reply]

How about a precisely placed array of smaller lenses ? StuRat (talk) 20:06, 28 July 2014 (UTC)[reply]

That would be the Rayleigh criterion, that I mentioned above. Red Act (talk) 20:48, 28 July 2014 (UTC)[reply]

I think the digital world has changed most of that at least for static images. In the same way that audio oversampling can have a 1-bit Sigma-Delta converter can shape noise out of the band of interest and achieve 18 bits or more of audio dynamic range, digital cameras with multiple images of the same object can be used to push resolution. Focus stacking is one technique. I believe there are others, that, even though single images are at the Rayleigh limit, multiple images at difference points in space and different focal planes can be combine mathematically to create a static image with much greater resolution than any individual one. I believe this is similar to having a much larger aperture with much less aberrations. --DHeyward (talk) 23:17, 28 July 2014 (UTC)[reply]

I'm not sure it works that way, but I work with audio-like signals, I'm not an expert in the image-processing field. Oversampling the image in the time domain simply allows you to reduce the noise at the source resolution, but not reveal smaller detail. See Oversampled binary image sensor for an example. Oversampling to increase resolution would have to happen in the spatial domain, which could theoretically work by snapping many quick images as the camera drifts over the subject, so the grid of pixels shifts slightly between each shot, but I would be very surprised to hear that the small number of samples would be enough to make an appreciable difference in resolution. I do vaguely remember hear about using a similar technique to get higher-quality stills out of blurry security camera footage, but I'm having trouble tracking down a good source. Katie R (talk) 13:54, 29 July 2014 (UTC)[reply]

It's possible to get a very high angular resolution with an array of separated telescopes; that's the principle behind astronomical optical interferometry. I can't find any evidence that optical interferometry has been tried from satellites, but interferometry at microwave wavelengths from satellites exists; see Interferometric synthetic aperture radar#Spaceborne. Red Act (talk) 15:02, 29 July 2014 (UTC)[reply]

So it's impossible at this time although there are some theoretical ways to do so. Thank you all for this interesting discussion and explanation. I've got what I want :).--115.73.31.225 (talk) 00:57, 29 July 2014 (UTC)[reply]

I have two questions, each of which drives toward the same basic point: 1. If the Nile dried up today, what physical evidence would exist a thousand years from now to tell us that it flowed south to north rather than north to south? and 2. Can you determine the direction of flow of a dry river without knowing where its source was or where it emptied? Evan ^{(talk|contribs)} 23:51, 28 July 2014 (UTC)[reply]

You might want to ask the members of Wikipedia talk:WikiProject Rivers.

—Wavelength (talk) 00:04, 29 July 2014 (UTC)[reply]

Wavelength, we shouldn't encourage people to ask knowledge questions on pages meant for discussing improvements to the encyclopaedia. The whole reason the reference desk was set up was to keep those questions off the project pages. SpinningSpark 00:46, 29 July 2014 (UTC)[reply]

Spinningspark, I meant that the original poster would invite editors with specialized knowledge to comment at the reference desk.

—Wavelength (talk) 01:20, 29 July 2014 (UTC)[reply]

The Nile has a prominent delta which shows where it carried sediment into the Mediterranean. 84.209.89.214 (talk) 00:41, 29 July 2014 (UTC)[reply]

The topography of the land, i.e. which way is "downhill", might be a clue. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:05, 29 July 2014 (UTC)[reply]

I hope we aren't facing confusion here because the Nile appears to run UP maps. HiLo48 (talk) 03:19, 29 July 2014 (UTC)[reply]

That would be more pathetic than I can imagine. In any case, the OP is talking one thousand years, which is fairly short on the geologic scale. Dry Falls, for example, has been around for like 20,000 years, and it's still pretty easy to figure out which way the river was flowing. The much less dramatic human-made earthworks leading away from Stonehenge are visible from the air (se Google Maps) ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:15, 29 July 2014 (UTC)[reply]

I don't think I was confused about... anything, actually. I got good answers, though, so thanks, everyone! Evan ^{(talk|contribs)} 16:12, 29 July 2014 (UTC)[reply]

Spacecraft on Mars are able to measure properties of the dried up rivers located there that haven't flowed for a million years. Figuring it out at the Nile after such a relatively short period of time should be a piece of cake. Erosion patterns would distinctively show flow direction - a protruding surface will be more highly worn on the side that the water is flowing against, and less worn on the sheltered lee side. Ancient river beds are occasionally frozen in time as "Mudstones" that show the ripples in the muddy bottoms - which also makes it really easy to figure out the water flow direction. SteveBaker (talk) 04:36, 29 July 2014 (UTC)[reply]

I saw examples on a recent trip to Central Australia. In Kings Canyon there are large areas of rippled rocks one finds oneself walking over. Nearby, is the Finke River, claimed by some to be the world's oldest river. It still runs sometimes, after really heavy rain, but most people just see a dry river bed, starting in a desert, and ending in a desert. The forms of erosion on rock surfaces can show which way the water has flowed. HiLo48 (talk) 04:53, 29 July 2014 (UTC)[reply]

I believe every river connected to the ocean flows into the ocean, and not inland from the ocean. The reason is simple: land is almost always above sea level, which is to say higher than the sea. Water in a river flows downhill, which is towards the ocean. Anybody who saw a dried-up Nile can immediately conclude that it flowed into the ocean, absent overwhelming evidence to the contrary.

The basic shape of the river should also tell you which direction the water flowed. Generally, small streams merge into tributaries, which then merge into rivers, which then merge into giant rivers like the Nile. So "uphill" is the direction where the river branches off and becomes smaller; "downhill" is the direction where the river merges into a bigger river. --Bowlhover (talk) 07:23, 29 July 2014 (UTC)[reply]

This question pertains to sedimentology, and can be partially addressed by the articles, Sedimentary structures and Paleocurrent. Plasmic Physics (talk) 08:06, 29 July 2014 (UTC)[reply]

Anecdote: A geology professor I once had (a stratigrapher) told the story of his finding, in some exposed strata, what he thought were imbricated pebbles indicating a direction of flow. Excavation revealed that they were, instead, the remains of the ribcage of a fossil whale. Deor (talk) 11:26, 29 July 2014 (UTC)[reply]

• The Amazon Basin once drained to the west but this is on a huge time depth, long before the dinosaurs went extinct. μηδείς (talk) 16:58, 29 July 2014 (UTC)[reply]

The English River Avon once flowed to the north and drained into the Humber, rather than into the Severn as it does today. Perhaps our article will give you pointers. --TammyMoet (talk) 19:57, 29 July 2014 (UTC) Well it doesn't, but this article does. As it says, it once drained into the River Trent, but during the Wolstonian glacial period that route became blocked, and after the Ice Age ended, it flowed to the south-west. Perhaps I ought to add it to the article.--TammyMoet (talk) 20:05, 29 July 2014 (UTC) Done! --TammyMoet (talk) 20:16, 29 July 2014 (UTC)[reply]

• Yes, and this sort of thing happened innumerable times with the rivers draining the Great Lakes as well as the Columbia and related systems on the NA west coast. The entire outflow of the St. Lawrence once flew through the Hudson. A look at a topographical relief map of the area is enlightening. μηδείς (talk) 20:39, 29 July 2014 (UTC)[reply]