Wikipedia:Reference desk/Archives/Science/2017 May 25

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May 25

Can sea water be purified and made into fresh water?

There is more water than land on this planet, Earth. And yet, some people complain that there is not enough fresh water. Now, I know sea water is not drinkable. But, water can be purified by various ways - reverse osmosis, distillation, de-ionization, filtration. And water can be collected from the rain. Earth is a very watery planet. Humans already collect sea salt from the sea. Why not the water as well? 50.4.236.254 (talk) 01:23, 25 May 2017 (UTC)

1) It takes a lot of energy and/or expensive facilities to desalinate the water.

2) It takes money and infrastructure to distribute that water inland.

Collectively, the result is that rich nations can do this, but not poor nations. As for collecting rain, they do this, but it doesn't always rain in all places. Large cisterns are needed to survive multi-year droughts, and those aren't always practical. Then the flooding carries soil inland, where it can nourish plants there. StuRat (talk) 01:25, 25 May 2017 (UTC)

As for collecting rain, the problem is that it falls over a large area. So in many places the most efficient way to collect it is to let the water flow naturally into or over the ground until it reaches a river, which can then be dammed to create a reservoir. This is done in many places. (Added later: Obviously there are also many places where it won't work. For example, maybe the terrain is the wrong shape for the water to flow to a suitable location for a reservoir, or maybe the climate is so arid that the water evaporates before it can be collected.) --69.159.60.50 (talk) 21:55, 25 May 2017 (UTC)

Desalination of seawater / ocean water is actually pursued on a large scale in places where electric power is available but fresh water is scarce. Our desalination article describes the technological approaches used; in a nutshell, they are distillation and reverse osmosis, both of which the OP has already mentioned in the question. Here's a good list of Desalination facilities. --Dr Dima (talk) 03:06, 25 May 2017 (UTC)

There are two problems with water supply. One is that in some areas there just isn't enough to do everything that the people want to do with it. If they are rich enough, desalination is an option - though it is usually cheaper to pipe it in from further away. In other areas, there is plenty of water - but it isn't safe for people to drink. That is the real problem today - because it kills large numbers. Wymspen (talk) 14:08, 25 May 2017 (UTC)

• Reverse osmosis requires a pressure differential of about 50 psi, which we supply using pumps driven by electricity. But this pressure is equivalent to about 150 feet of rise. That means that desalinated seawater delivered to a town 150 feet above sea level is twice as expensive as that delivered to a town at sea level. So San Diego California may be able to use desalinisation but Reno cannot, even ignoring the cost of the pipeline. -Arch dude (talk) 15:41, 25 May 2017 (UTC)

Water purification is Wikipedia's article about large scale, municipal water purification. The article Desalination describes methods for extracting potable water from sea water. Blooteuth (talk) 16:37, 25 May 2017 (UTC)

You can extract pure water straight out of the atmosphere. The theoretically minimum energy required is then the Gibbs energy difference between the water vapor at the actual relative humidity r and at 100% relative humidity, which is -N k T Log(r) where N is the number of water molecules and T the ambient temperature. Count Iblis (talk) 22:04, 25 May 2017 (UTC)

Soil formation on the bank of the Nile river

Some time ago, I asked on the Humanities desk about the Fertile Crescent. The responders seemed more focused on rejecting the claim that the Fertile Crescent is a desert, even though I looked at the provided pictures and saw desert land. One person pointed out that the bank of the Nile river has soil and flooding, probably due to the seasonal tides, so it allows plant colonization. But, that still leaves a mystery for me. How can the Nile river bank be fertile while a sandy beach seems so barren? How is the soil formed in the first place, thereby allowing plant colonization on land? 50.4.236.254 (talk) 01:32, 25 May 2017 (UTC)

Plants have a lot to do with it. Many plants can't take salt-water, so don't grow on ocean beaches. Also, the major waves and tides on ocean beaches are rough on plants. But river banks tend to be more gentle, allowing plants to grow roots there, which then retain the soil which would otherwise wash downstream. StuRat (talk) 01:54, 25 May 2017 (UTC)

If you want some additional reading on the Nile, Wikipedia has an article titled Flooding of the Nile which is sadly a bit brief, but hints at some importance including the deposition of silt from upstream sources, an important source of nutrients. The Wikipedia article titled Ancient Egyptian agriculture has more information. This brief article from the Smithsonian Institution also discusses the importance of the nutrient-rich silt carried by the Nile from volcanic sources further south. This article at Britannica discusses the Nile Valley soil formation in more details. this book hints at the importance of fresh alluvium from the Nile inundations. This article is a rather detailed survey of modern Egyptian agriculture, with a focus on the soils of Egypt. If you really wanted to get detailed on the soil science this paper looks like a good launching point. I hope some of that reading helps explain things. --Jayron32 03:41, 25 May 2017 (UTC)

This makes me happy. :) 50.4.236.254 (talk) 04:27, 25 May 2017 (UTC)

How did the common people come to define "organic" to mean "without pesticides"?

There was one time when I asked my chemistry instructor about the meaning of the term, "organic". He said, "comes from life". I didn't get it, because then I wondered whether my fruits and vegetables in my refrigerator and on my table were "organic". They came from life, so I figured they must be organic. Later, I found out that "organic" meant "without pesticides". How did the common people come up with this definition? In terms of agriculture, if a large conventional farm borrows "organic" farming practices for better environmental management and increased yield, then has the farm suddenly changed into an "organic farm"? And in terms of pesticides, are large herbivores (deer, rabbits) considered "pests" too? The farm basically grows a lot of food intended for human consumption. But, given that the plants occupy a significant amount of land, and that the plants are edible, it stands to reason that hungry deer and rabbits and field mice would happily munch on the plants, reducing yield. Also, these large pests are vertebrate mammals, so they may be very phylogenetically related to humans, making it harder to treat by pesticide poisoning. I mean, they may be killed, but if a poison intends to kill them, the poison can also kill humans due to the shared biology. 50.4.236.254 (talk) 04:54, 25 May 2017 (UTC)

Organic in the broader biological sense and organic in the Organic food culture sense are not related. It's like how when real doctors use the word "medicine," it's a very different word from when homeopaths use the term. You can read more about the disadvantages of organic farming in our article on the subject. Ian.thomson (talk) 05:01, 25 May 2017 (UTC)

There's a significant flaw in that article: the word "recent". First it's undefined, a weasel-word. Second, this concept has been around for well over 50 years. It was referenced in a Stan Freberg recording called The United States of America Volume One: The Early Years - a satirical history recorded in 1961, in which he has an Indian trying to persuade Columbus to eat some "organically grown vegetables." The casual use of that term indicates it was well-established by 1961. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:26, 25 May 2017 (UTC)

EO says the meaning "free from pesticides and fertilizers" dates to at least 1942.[1] ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:28, 25 May 2017 (UTC)

Organic does not mean without pesticides. See Organic farming#Pesticides. Pesticides used in organic farming can have additional safety concerns, as it is prohibited to process them from their "natural" state to be safer. 91.155.195.247 (talk) 05:06, 25 May 2017 (UTC)

• It is important to note that words, in different contexts, can have different meanings, and that is OK, and completely normal and how all languages, including English, works. So, in the context of Chemistry, organic means "chemistry of carbon"[2] and in the context of farming, it means "grown without the use of man-made chemicals or GMOs".[3] Some people get pissy about this, and I don't know why, because they can happily carry other words in their brains that have different meanings in different contexts. "Organic" is not special nor difficult in this regard. --Jayron32 12:47, 25 May 2017 (UTC)

Chemists worry about chemophobia, I think. shoy (reactions) 13:27, 25 May 2017 (UTC)

• Look at the history through the Soil Association. This goes back to WWII, their first certification for organic farms was in the mid '60s. Andy Dingley (talk) 13:17, 25 May 2017 (UTC)

• According to our organic food article, this usage was originated by Lord Northbourne in a 1939 book, based on his conception of "the farm as organism". Looie496 (talk) 13:54, 25 May 2017 (UTC)

• Think of "organic" as meaning "100% organic". So, if even a tiny portion of the chemical residue on the skin was made in a lab, that's not "organic". However, there are organic pesticides, like vinegar: [4]. Lab-produced pesticides have a history of being dangerous to people, however, with Round-up being the latest.

• Large herbivores can be kept out by non-chemical means, like fences, or dogs to chase birds away. StuRat (talk) 14:47, 25 May 2017 (UTC)

Thank you for giving me an opportunity to shit on a common chemophobic claim: "organic" pesticides can be toxic as well. See pyrethrin for example. Someguy1221 (talk) 06:48, 26 May 2017 (UTC)

That " as meaning "100% organic"" claim is sheer OR, matching neither the chemists' definition, nor the Soil Association's. Andy Dingley (talk) 15:55, 25 May 2017 (UTC)

This isn't about how chemists define organic, it's about how food consumers do. StuRat (talk) 16:23, 25 May 2017 (UTC)

The US Food and Drug Administration has a set of standards that define what can be labeled "organic" in the United States[5]. These standards have nothing to do with whether the product was treated with a substance "made in a lab". And yes, some synthetic pesticides are allowed on organically labeled food, as well as a variety of non-synthetic pesticides, some of which are quite dangerous to humans and/or damaging to the environment, such as boron, copper sulphate, and rotenone.[6] CodeTalker (talk) 22:12, 25 May 2017 (UTC)

The OP's question may be more suitable for the Languages reference desk. The chemistry teacher's answer "organic means comes from life" can be challenged in the case of Urea, an organic compound now synthesized from inorganic starting material. The common people did not come up with a definition of "organic" to be used as a marketing category for farm products that often carry a premium price or are less superficially attractive; this usage is agenda driven, see this outline. To be marketable as a Pesticide, a product ideally harms only small pests that cause harm and elicit no sympathy. For control of animals larger than an insect with which one might feel empathy, a humane person may prefer to employ an Animal repellent instead of a lethal biological agent that is predictably destructive to humans, their pets and the enviranment. Blooteuth (talk) 15:16, 25 May 2017 (UTC)

The OED has literally dozens of different senses of the word organic, many of them obsolete, but the OP might be interested in the definition for chemistry (first cite 1822): " Originally: relating to or designating compounds which exist naturally as constituents of living organisms or are formed from such substances (all of which contain carbon and hydrogen). Later: of, relating to, or designating any compounds of carbon (other than certain simple compounds such as oxides, carbides, carbonates, etc.), whether of biological or non-biological origin", and for farming (first cite 1942): " Of a method of farming or gardening: using no chemical fertilizers, pesticides, or other artificial chemicals. Also designating a farmer or gardener utilizing such a method, or a farm on which the method is employed.". Dbfirs 05:52, 26 May 2017 (UTC)

"Organic" refers to running the farm as an organism, where crops are rotated and animals are part of the system: cows help refresh fallow soil, chickens get rid of weeds and bugs, pigs dispose of waste. It is in contrast to specialized farming, where only one crop or animal is raised, hence the need for artificial fertilizers and pesticides. Organic standards limit the use of pesticides, which is one of the reasons people buy them, but not why they are called organic. TFD (talk) 06:27, 26 May 2017 (UTC)

Human size and power of blows, strikes, kicks

Is there an optimal average size for maximum striking power? The rationale is that although you'll need mass, maybe from a certain mass on your speed start going down. Would then someone be stronger but lighter due to this higher speed? --Hofhof (talk) 10:41, 25 May 2017 (UTC)

The evidence from boxing and shot-putting would I say indicate otherwise. Anyway do you really think anyone could stand up to being whacked by the tail of a whale? I guess there is a limit eventually but it must be pretty huge. Dmcq (talk) 11:33, 25 May 2017 (UTC)

Yes, but for the tail of a whale the rule still applies. Maybe other animals are much faster, even if less massive, and can hit harder. Many other factors also apply, starting by the fact that claws would be much more damaging than the smooth skin of a whale.

Where's the evidence from boxing and shot-putting? Has this been analyzed scientifically? AFAIK, the athletes are massive, but no one is like 400 pounds, which would prove my point. Hofhof (talk) 11:41, 25 May 2017 (UTC)

Sorry I didn't know you were trying to prove a point. Dmcq (talk) 12:20, 25 May 2017 (UTC)

I mean, it's a hypothesis, it can be refuted, or not. — Preceding unsigned comment added by Hofhof (talk • contribs) 13:41, 25 May 2017 (UTC)

We have had 400 pound wrestlers, even up to 800 (Happy Humphrey): [7]. However, if we move up to 1000 pounds, you have a point. The limits may be more due to them dealing with their own weight, than the relative effect of blows. At 1000 lbs the human body may be seriously injured by falls, and just moving around takes a huge effort. Of course, that's because the design of the human body doesn't support that type of weight well. Larger animals can manage that weight just fine. When fighting a much larger wrestler, the strategy should be to hit and run, and don't allow them to hit you or get hold of you. Just let them tire themselves out chasing you. StuRat (talk) 14:54, 25 May 2017 (UTC)

Well, when fighting a much larger wrestler, you probably do the same thing as when fighting a smaller man - you follow the script. --Stephan Schulz (talk) 12:04, 26 May 2017 (UTC)

What matters is if you can do these exercises. Count Iblis (talk) 19:27, 26 May 2017 (UTC)

16 Psyche on earth

If 16 Psyche, the metal asteroid, was somehow to be gently brought to earth (not a giant crash), would the mass be enough to disturb the earth's orbit? What changes in position and duration would occur? -- SGBailey (talk) 13:54, 25 May 2017 (UTC)

• If we assume that the asteroid magically teleports onto the Sahara without any immediate change to the Earth's rotational motion except the added mass, none because mass does not matter for orbits (also, 16 Psyche has a negligible mass compared to the Sun's). On a fundamental level, this is linked with the equivalence principle (saying that the "mass" used for inertia in Newton's second law and for gravity in the gravitation law).

However, if the asteroid is somehow towed towards Earth, surely while it is in transit close to Earth it would attract it and hence modify its orbit. By how much would depend of how long the towing takes etc., though I would guess "not much". Tigraan^{Click here to contact me} 14:28, 25 May 2017 (UTC)

• Agreed. The Earth's mass is some 200,000 times more, so any effect would be minimal. StuRat (talk) 15:01, 25 May 2017 (UTC)

From our archives, I dug out: August 2012, "What If..."

“ We get this question a lot. If I may quote myself, from March of 2012, when I quoted myself from a similar question in September of 2011: (I have taken some liberties to modify the quote to increase relevance to the current question):

"The answer to this type of physics question always depends: how would [the asteroid magically transport to a position near Earth]? If you can specify that, we can follow through with the consequences by solving the equations of motion for the Earth-Moon[-Asteroid] system.

For example, if you hypothesize that a giant comet large and fast enough to change the [asteroid's orbital position] impacted [16 Psyche], .... well, we would need to calculate the effect that such a large comet has on the orbits of Earth and everything else in the solar system, too. We could solve that problem by setting up an n-body problem to model the solar system, including Earth, Moon, Sun, and other planets; and we would use perturbation theory to study how sensitively the system reacts when we add in a new comet on a course to impact the [asteroid]. The results are difficult to compute, but this can be done in a reasonable amount of time with a reasonable amount of effort.

...

On the other hand, if you just want to make something up, "just imagine" that the [asteroid] magically changes its [orbit], all bets are off. We can't meaningfully speculate what consequences follow when one law of physics breaks "because of magic." Anything could happen. Everything we know about the way the [asteroid] orbit couples into the Earth's rotation depends on the rules of physics as we currently understand them.

”

So - does that answer your question? Anything. Anything could happen.

You cannot magically transport mass from one point to another - in any circumstance, let alone in orbital mechanics. It takes a change in energy and momentum to change an orbit - even if the final position has no net motion relative to Earth, and even if the relative velocity exactly equals zero at the moment of contact with Earth. You have to do something to cause the energy and momentum of the asteroid to change; how you do so must be in compliance with these conservation laws, and how you do so would profoundly alter the outcome. The ensemble set of these conservation laws, ostensibly, constitute the single absolute most important-est and most inalienable part of our understanding of our physical universe. If you try to bend them for the purposes of the hypothetical, all you get is the principle of explosion - it is absolutely meaningless to proceed from a logical falsehood.

To put the absurdity of the original question in to terms that you might be able to explain to your kids: "Imagine that you knocked a brick off of the top of the roof of a very tall building, and the brick dropped down towards the ground. But, instead of falling down really fast and impacting the ground, the brick just remained stationary and rested on the ground and didn't move. (Not a giant crash). When it hits the ground, does the brick shatter on impact?" Yes? No? Use your imagination! The question asks about a situation that doesn't even make sense!

Nimur (talk) 15:06, 25 May 2017 (UTC)

If Asteroid mining ever becomes feasible, 16 Psyche is believed to contain 1.7×10¹⁹ kg of nickel–iron, which could supply the world production requirement for several million years. Planetary Resources and Deep Space Industries are companies that are attracting investors to their plans for asteroid exploitation though this speculative list of target asteroids does not include 16 Psyche. The proposal of towing that 200 km (120 mi) diameter body to a gentle (!) touchdown on Earth is so daunting that we can only consider an exploitation scenario where manageable amounts of ore are first extracted and processed on the asteroid before they are shipped to Earth. Long before change to Earth's orbit becomes evident, this activity would have political repercussions on Earth (now addressed by the UN Office for Outer Space Affairs) and likely alter the trajectories of other asteroids with unforseeable consequences. Blooteuth (talk) 16:23, 25 May 2017 (UTC)

I remember when you first posted that, Nimur. I liked it then and I like it now, but please note that the OP said nothing about magic; they only suggested that its landing be non-catastrophic, which brings up any number of real world possibilities that enable controlled descent (albeit difficult given the proposal). Matt Deres (talk) 16:29, 25 May 2017 (UTC)

Indeed - and if he were to precisely explain the mechanism of mass transference - by describing a collision, or explaining a rocket-powered scheme to change the trajectory of the planet - I would be very happy to start pointing to real and useful resources that would help explain the outcome! One of my favorite books is To Rise From Earth: An Easy-To-Understand Guide to Spaceflight, and it shows the reader how to set up the basic problems in orbital mechanics. That book is written for a technically-inclined, but non-rocket-scientist, audience.

I'm sort of keen on running the math myself to figure out how much energy you'd have to expend if you attached rockets and conducted a Hohmann-transfer for the entire asteroid. I'm sort of curious whether we're in the ballpark of the order of magnitudes achievable with chemical rockets, or if we'd really need to dive into deep science-fiction to make it happen.

Nimur (talk) 22:16, 25 May 2017 (UTC)

Even if by some Non-Magical Magic the 200 km sized object was to land on Earth with zero relative velocity, it would not stay still. Rather, it would collapse under its own weight: the max mountain height on Earth is on order of 10 km, because taller objects produce pressures at their base which exceed the pressure of elasto-plastic transition in the material. Two things will happen: (a) the object will collapse and spread out as a pancake, and (b) the continental crust will deform and sink and/or flow outwards from the location of the touchdown. This is a Bad Thing. Dr Dima (talk) 17:27, 25 May 2017 (UTC) Also of note, the continental crust average density is 2.7 g/cm3, about a third of the typical Fe-Ni alloy density. There is therefore a distinct possibility that some (or all) of the Psyche material will end up sinking straight into the Earth mantle and towards the core. Oops. Dr Dima (talk) 17:55, 25 May 2017 (UTC)

Agree that isn't good, nevertheless, for two-body problems often it's the case that M>>m, where here M is the Sun's mass and m is the Earth's mass, and this assumption holds true when 16 Psyche's mass is added as well. However, more precise and accurate models do not make that assumption such that both M and m affect their orbital period and separation. Solar mass M_☉ is about 332946 M_E (Earth mass) (I've a textbook that says about 300,000 times so StuRat is not too far off the mark above). Currently, our article on the Sun shows that we know the Sun's mass to within about one M_E, hence any simulations of this are not going to be able to include mass changes smaller than that. Still, I am certain that with conservation of angular momentum we can determine how much the year is shortened by some tiny amount even if it's not measurable. This is because bringing in an object from beyond the Earth's orbit increases its angular speed (much like a skater spins faster when they pull their hands in) and so the interior orbital periods are shorter consequently and that any accretion of mass on Earth simply increases its gravitational acceleration towards the Earth's and Sun's common barycenter and that brings about a faster and tighter orbit (thereby conserving momentum too). This imaginary barycenter is the system's mass center which has to move closer to the Earth as their mass imbalance is reduced. Conservation of angular momentum for a mass m on a string of length r requires that (mr^2)/T be some constant where T is the orbital period. Thus given this constant the new radius is r=sqrt(constant T/m) where m is the new mass and T the new period which is the parameter we want to solve for by eliminating r using the equation for two orbiting bodies (I already linked to it). To further simplify that work, note that we have to include the mass and momentum of the asteroid body as it nears us. So the net mass m cancels and we really only have r=sqrt(constant*T) for the constant ((r^2)/T). Also, one must assume a greater precision than we have for the Sun's mass (by appending a spherical cow of zeros beyond the current precision that we have) to get different mass totals, but we are not interested in their absolute values anyway, only the magnitude of relative change that occurs for these parameters. @SGBailey: I'm not a physicist, but I did take this stuff in high school and college like decades ago... thus some of the things I learned have stuck with me more than others, but I hope this helps more thoroughly answer your question. -Modocc (talk) 21:47, 25 May 2017 (UTC)

@Dr Dima: I agree what you say is true, but ... well, a while ago I asked about mantle hotspots and learned that ordinary granite is a rheid. So I realize now to take some of these terms about plastic flow with a grain of... caution. When you say that the asteroid would collapse and cause the crust to buckle, are you talking about a geological timescale, or something more dramatic? Wnt (talk) 23:46, 25 May 2017 (UTC)

@Wnt: This is not really an appropriate place for original research, and I don't have solid literature to cite because the whole scenario is obviously hypothetical. However, since pressure wave travels at least with a speed of sound, the material near the point of contact between Psyche and Earth will start to yield within seconds if not faster. The whole of Psyche will then proceed in a nearly free fall for at least a while, until the pressure force produced by compression and heating of both crust and asteroid material will sufficiently exceed the Psyche weight to decelerate and stop the Psyche fall. This will be followed by a rebound, etc. I think. Dr Dima (talk) 01:27, 26 May 2017 (UTC) (To be clear, when I say "Psyche weight" and "Psyche fall" I don't at all imply that it will behave as a solid. Rather, it will behave more like a blob of liquid, given the pressure values produced). Dr Dima (talk) 01:32, 26 May 2017 (UTC)

BTW, here's another way to look at it. at 100 km above the surface of the Earth (which would be the initial position of Psyche's center of mass, as well as its equatorial plane), a potential energy of 1 kg of iron is mgh = 1 kg * 10 m/s2 * 100000 m = 1e6 Joules. This energy has to go somehwere as the iron falls down to Earth. Heat capacity of iron at room temperature is 444 J / kg K, and latent heat of fusion (melting) is about 1e5 J/kg; so assuming half the energy (5e5 J per 1 kg) goes into heating the iron and half goes into heating air and crust material, the temperature of the Psyche material will, on average, rise by over 1000 K. It will not all melt, but some of it will actually melt, and the rest will be rather unpleasantly hot for a while :) --Dr Dima (talk) 02:41, 26 May 2017 (UTC)

@SGBailey: All else equal, if 16 Psyche's mass was added to the Earth's mass then the year and the semimajor axis distance to the Sun would be shortened by about 0.72 milliseconds and 1.7 meters respectfully. I calculated these from the equation for two orbiting bodies: $T=2\pi {\sqrt {\frac {a^{3}}{G\left(M_{1}+M_{2}\right)}}}$ and $r={\sqrt {T*constant}}$, where the $constant={\frac {r^{2}}{T}}$ is from the conservation of angular momentum of any fixed mass constrained to radii r with periods T. Letting r = a, solving for T gives: $T=(2\pi )^{4}{\frac {constant^{3}}{G^{2}\left(M_{1}+M_{2}\right)^{2}}}$. Also, $M_{1}+M_{2}={\frac {(2\pi )^{2}{\sqrt {\frac {constant^{3}}{T}}}}{G}}$. Therefore, $\left(M_{1}+M_{2}\right)+\Delta M={\frac {(2\pi )^{2}{\sqrt {\frac {constant^{3}}{\left(T+\Delta T\right)}}}}{G}}$ and $\Delta T=T_{2}-T_{1}=(2\pi )^{4}{\frac {constant^{3}}{G^{2}}}({\frac {1}{(\left(M_{1}+M_{2}\right)+\Delta M)^{2}}}-{\frac {1}{\left(M_{1}+M_{2}\right)^{2}}})$. Solving for r instead $\Delta r={\frac {(2\pi *constant)^{2}}{G}}({\frac {1}{\left(M_{1}+M_{2}\right)+\Delta M}}-{\frac {1}{\left(M_{1}+M_{2}\right)}})$. For our Earth the constant is about 7.0915e+14 m²s^-1 (for r=149598023000 m (the Earth's orbit's semimajor axis) and T=31558149.5 s) and gives a total mass 1.9885e+30 kg within the error range given at Solar mass. I then crunched these numbers with WolframAlpha here and here. -Modocc (talk) 07:07, 29 May 2017 (UTC)

It's enough of a difference in Earth's orbit to potentially alter who gets hit by some impact events. :-) --Modocc (talk) 08:15, 29 May 2017 (UTC)

Can hormones be secreted by the endocrine system only?

or it's possible to secrete hormones by another way in the body17:10, 25 May 2017 (UTC) — Preceding unsigned comment added by 93.126.88.30 (talk)

Wikipedia is your friend. Please read endocrine system, juxtacrine signaling, paracrine signaling, autocrine signaling, neurotransmission, and neuromodulation. These articles address the many specific aspects of your question. --Dr Dima (talk) 17:43, 25 May 2017 (UTC)

Part of the problem with definitions like this is that they are not divinely mandated or requirements of law or anything like that; definitions are human created for human convenience and as such, suffer from human uncertainty. Depending on how you establish your terms, you can set up rather obvious answers to questions like this. For example, the common definition of the terms endocrine system and hormone establishes a tautology such that we define the endocrine system as "The parts of the body that produce hormones" and thus hormones as "substances produced by the endocrine system", your question then answers itself in uninteresting ways; because the relationship between hormones and the endocrine system is tautological, there's no possibility that one could answer in the negative; if we should discover hormone tomorrow that was being produced by a part of the body that was not previously counted as part of the endocrine system; that organ would then be an endocrine organ because it is producing a hormone, and that's what endocrine organs do. There are, of course, organs which are part of the endocrine system and also part of other systems because they have multiple functions; for one example, the pancreas produces the hormone insulin, thus is an endocrine organ by definition, but it also produces Carboxypeptidase, which is a digestive enzyme, and thus that makes the pancreas a digestive organ. You can play with the fuzzy edges even more than that; neurotransmitters are not normally considered hormones because they don't use the circulatory system to get around the body, which is one of the sine qua non of hormones, and what makes them different from other secretions. However, there are some compounds, like Epinephrine, which are both hormones and neurotransmitters; but that does NOT make nerve cells that produce it endocrine cells; because when it is used as a neurotransmitter it isn't acting as a hormone. The TLDR version is this: You can't make these categories exclusive for individual components, because then you create contradictions (that is, you can't demand that the pancreas ONLY be part of the endocrine system) and you also shouldn't get too hung up on uninteresting tautologies. Instead, the more interesting use of your brain power is to understand process and relationships, rather than getting hung up on definitions. --Jayron32 13:41, 26 May 2017 (UTC)

Solar and lunar eclipse in Toronto

When was the last time that the City of Toronto observed the lunar and solar eclipses? Donmust90 (talk) 23:40, 25 May 2017 (UTC)Donmust90Donmust90 (talk) 23:40, 25 May 2017 (UTC)

You can work this out yourself by researching at Lists of solar eclipses and Lists of lunar eclipses. --Jayron32 00:39, 26 May 2017 (UTC)

Technically "never" as lunar and solar eclipses never happen at the same time. They are typically two weeks apart. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:47, 26 May 2017 (UTC)

At least! —Tamfang (talk) 08:07, 26 May 2017 (UTC)

Or to nitpick in a different way, never, because cities do not have qualia. --Trovatore (talk) 09:56, 26 May 2017 (UTC)

Often, though not always, lunar and solar eclipses will occur in "pairs" - about two weeks apart. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:45, 26 May 2017 (UTC)

Any lunar eclipse is visible from about half the Earth, so this basically just asks when there was a lunar eclipse when it was night-time in Toronto—which, from the lists linked above, would be February 11 this year. However, to actually observe the eclipse the sky would have to have been clear, and I don't think it was.

For solar eclipses, each one is only visible from a narrow track. This page links to a set of maps of such tracks, each map covering a 20-year period, over a span of thousands of years both past and future. If you look at the 5 most recent maps, [8] [9] [10] [11] [12], you will see that the most recent annular eclipse visible in Toronto was in 1994 (and I remember that that was a clear day, so it was visible) and the most recent total solar eclipse was in 1925 (but I don't know about the weather then). --69.159.60.50 (talk) 15:42, 26 May 2017 (UTC)

There are solar eclipses that don't even have paths. Partial eclipses. Also the penumbras of total or annular eclipses. Those can be 10,000 kilometers wide when the shadow's at the Arctic and equator simultaneously. Or any other time an eclipse is on the horizon and (near) overhead simultaneously. There are even total and annular eclipses that have no path. The centerline never touches Earth's surface and the totality barely touches it leaving a small blob instead of a path. Sagittarian Milky Way (talk) 23:01, 26 May 2017 (UTC)

To look at it that way, there is a perpetual "solar eclipse", because there is always a cone-shaped shadow cast by the moon. When that shadow happens to touch the earth, we call that a solar eclipse. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:40, 27 May 2017 (UTC)

Touch the Earth how? In this graph the eclipse "path" is the fan-shaped blob about the size of Tasmania. The centerline is not on the Earth. (or at least, it's not on the idealized (equatorial radius?) Earth. The gamma is minus 1.0000 Earth radii so it's really close.) The partial eclipse is the gigantic thing that goes from the tropics to Antarctica even though the other side falls on outer space. P.S. the perpetual "solar eclipse" is not perpetual because Earth hides the Sun every total lunar eclipse. Sagittarian Milky Way (talk) 07:24, 27 May 2017 (UTC)

The cone-shaped shadow is always there, and sometimes that cone intersects the surface of the earth. Hence, an "eclipse". ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:14, 27 May 2017 (UTC)

There​ are 3 cone-shaped shadows, the umbra, antumbra and the penumbra. The cones are not always there. If you consider the refracted, red, indirect sunlight of a total lunar eclipse to always make the cone then you should also call total solar eclipses annular since moonscapes can be at least 480,000 times darker whenever eclipsed while total solar eclipse landscapes are only ~50,000 times darker. Even the corona alone is only ~420,000 times darker than the regular Sun (which isn't visible in central lunar eclipses anyway as the naked eye corona can only be about 1.5° wide while the Earth is 2° wide from the Moon). Also the Moon's "umbra" when it's totally eclipsed is several times shorter than when it isn't eclipsed because the Earth is 4 times bigger than the Sun in the Moon's sky. Is it really the same cone if it's 150,000 miles shorter and made by moonscapes so dim as to be invisible to the naked eye? (a Danjon scale zero "black eclipse" which happens after severe volcanic eruptions) Sagittarian Milky Way (talk) 20:34, 28 May 2017 (UTC)

The moon always casts a shadow. Or three shadows, if you will. But it's always there (except during a lunar eclipse, when obviously the sun is obscured by the earth). If you happen to be inside the shadow(s), you'll see an eclipse... even if you're flying through space at the right time and location. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:43, 29 May 2017 (UTC)

That's true. Fun fact: The Moon casts that shadow on an outer planet not too infrequently. It's penumbra is gigantic at that distance (up to hundreds of Jupiters wide) but the annular solar eclipse is so mild the planet getting dimmer probably cannot be detected from Earth. Here's the article. Sagittarian Milky Way (talk) 05:39, 29 May 2017 (UTC)

And to answer the solar half of the original question, the last solar eclipse observed at Toronto was seemingly either Solar eclipse of June 10, 2002 or Solar eclipse of December 14, 2001, both of which occurred near sunset in south-central Canada, and it's possible that one or both of them occurred too late for viewers in Toronto to see them. Nyttend (talk) 12:00, 29 May 2017 (UTC)

No, it was the partial phase (of course) of the partial eclipse of 10/23/14. The Toronto downtown airport weather record says it was clear. Sagittarian Milky Way (talk) 19:48, 29 May 2017 (UTC)

Hm, you're right; I don't know how I missed it earlier. Nyttend (talk) 21:29, 29 May 2017 (UTC)