Wikipedia:Reference desk/Archives/Science/2010 September 15

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September 15

Lenses

If you were to take a 55-200mm lens, like mine, with a minimum focus distance of 3.6 ft, and add a reversed 30mm f/1.4 lens, supposing with a minimum focus distance of 16 inches, as done here, what would the combined lens be like? What would be the focal length, f-number, minimum focus distance, etc.? --The High Fin Sperm Whale 00:33, 15 September 2010 (UTC)

At Lens (optics) there is a familiar equation for "compound lenses," but it is restricted to two thin lenses in contact,with another related formula for use when there is a known space between two thin lenses. It still might be used as a first approximation for your two compound lenses with some space between them. That said, it suggests that the zoom at the "normal" 55 mm setting plus the 30mm would combine to have a 19 mm focal length, and the zoom set at 300 mm plus the 30 mm would combine to a 27 mm focal length. No idea how the F stop, depth of field and aberrations would come out. See also Camera lens and Photographic lens design. Edison (talk) 23:07, 15 September 2010 (UTC)

THF and bleach

I'm trying to make hydroxy-tetrahydrofuran (a cyclic hemiacetal). On paper anyway.

Which would appear to be the more pragmatic (cheapest/simplest/fastest) route: THF + N-Bromosuccinimide, then react THF-Br with potassium iodide catalyst and potassium hydroxide?

THF + Bleach? Would I make any dangerous amounts of ether peroxides? (analogous to diethyl ether peroxides). Would a catalyst like TEMPO be worth it? (ultimately the end product is gamma-lactone).

Are there any other chemicals that are excellent for alpha-substitution?

John Riemann Soong (talk) 00:56, 15 September 2010 (UTC)

Have you tried looking at our article on gamma-Butyrolactone? Physchim62 (talk) 04:00, 15 September 2010 (UTC)

Yes I have, but it doesn't provide a lot of info. I'm curious about general mechanisms. Also comparing hydroxy-THF to sugars -- how much would the open/ring equilibrium differ? John Riemann Soong (talk) 18:47, 15 September 2010 (UTC)

RuO₄ (usually used as catalytic ruthenium salt and a stoichoimetric cheap oxidant--see article) is wickedly strong alpha-oxidant. Converts diethyl ether to ethyl acetate in good yield within minutes if I recall. I used to do a reaction with that as the oxidant in which I carefully used drops of ether or some other agent to quench the reaction/consume any unreacted oxidant...if I didn't, the reaction reliably spontaneously ignited when I used large amounts of ether in air during the workup/extraction. DMacks (talk) 20:09, 15 September 2010 (UTC)

Wow thanks. I note that you didn't say that the oxidant converted diethyl ether to acetic anhydride. That what I was worried about too -- that I would get alpha substitution on both sides of the ethoxy oxygen. I suppose once alpha-oxidation has occurred once, hydroxy-THF becomes especially reactive and quickly undergoes a second oxidation, and once an ester has formed, the former alternate alpha-substitution site is no longer reactive? John Riemann Soong (talk) 20:16, 15 September 2010 (UTC)

DOI:10.1080/00397918008064223 is a systematic study of this reaction. It cites as precedent DOI:10.1139/v72-501, the reaction specifically on THF, and was expanded cited by DOI:10.1246/cl.1993.1513, which disusses/expands the THF case to other catalytic-metal-oxide/stoichiometric-oxidant recipes. DMacks (talk) 20:38, 15 September 2010 (UTC)

More to your original question (rather than overall apparent goal), the hydroxide S_N2 step may be a problem: competing E2. On the other hand, acid-catalyzed hydration of the enol ether product there is easy. An alpha-halogen is a really good substrate for nucleophilic attack, so 1) not sure you need to go up to iodide as a better leaving group first, and 2) not sure you need to be strongly basic to displace it. I've done a reaction that gave the tetrahydropyran analog, which was pretty dangerous to handle, so I added methanol and a trace of acid, and converted the bromo to methoxy pretty efficiently. Acid-catalyzed S_Nx reaction where the leaving group is not basic! Never quite figured out if it was thermal S_N1-like vs thermal elimination followed by acid-catalysed addition. DMacks (talk) 20:38, 15 September 2010 (UTC)

Thanks for all the info. I still admire the elegant simplicity of oxidations by hydrogen peroxide or bleach sometimes -- so suppose I wasn't picky about purity or yield as long as the product was convenient to extract. Is bleach a competent alpha-oxidant, especially in the presence of simple metal (or Lewis acid) catalysts like ferric chloride (from adding HCl to a rusty iron nail)? John Riemann Soong (talk) 20:54, 15 September 2010 (UTC)

Bleach is usually quite a "messy" oxidant – it's fine if you want the oxidation to go all the way, but it is hard to control for intermediate products. It's also basic, so you would risk opening any lactone/anhydride ring to form GHB or succinic acid. Physchim62 (talk) 21:03, 15 September 2010 (UTC)

Conker Trees

Should conker trees be loosing their leaves at this time of year in the UK? I thought it was way too early, but I see several conker trees, including my pet tree, all with their leaves going brown and dying. No other species of tree are loosing their leaves yet either 82.44.55.25 (talk) 12:56, 15 September 2010 (UTC)

Have a look at the bark. It maybe suffering from bleeding canker which can cause premature leaf drop. We cannot offer medical advice on Wikipedia so I suggest you take your pet tree to a certified arborist for a second opinion. The Royal Horticultural Society has more information on conker diseases on their website [1] and the Forestry commission has photos of diseased trees. [2] If your trees are on land maintained by the local council, you can email them to ask what they are doing about it. --Aspro (talk) 13:12, 15 September 2010 (UTC)

Just to be pedantic, but by definition, medicine applies only to humans, thus medical advise is not applicable in diagnosing or treating disease in plants. Googlemeister (talk) 13:52, 15 September 2010 (UTC)

I think it was a joke. And, to be even more pedantic, you meant "advice". Ghmyrtle (talk) 14:06, 15 September 2010 (UTC)

and fwiw, it's losing rather than loosing (although in a sense, of course, it is loosing also...common mistake. --Tagishsimon (talk) 13:21, 15 September 2010 (UTC)

Could it be related to this moth infestation? - obviously not just a local problem. See Horse-chestnut leaf miner. Ghmyrtle (talk) 13:34, 15 September 2010 (UTC)

Almost certainly. Incidentally, I wouldn't trust the zoologists claim in the link that "it's doing no harm to the trees". It doesn't take a genius to realise that a tree with no leaves or brown leaves won't make as much sugar as a healthy tree. I've observed (not seen any studies so an OR warning) that the number of conkers is dramatically decreased when the trees are infested and this will obviously cause problems if it carries on for years. If you want to try and stop the moths spreading further throughout the UK, it might be worth sweeping up the leaves that fall onto the ground and disposing of them, as this is about the only proven way to decrease the infestation (reference). The forestry commission have more info on the problem here. Smartse (talk) 15:00, 15 September 2010 (UTC)

...and here. Ghmyrtle (talk) 15:04, 15 September 2010 (UTC)

I live at the edge of an ancient woodland, and from where I sit I can see about 50% of the trees have turning leaves, and I can't see any horse chestnuts here. At a guess it has to do with this year's weather conditions. I agree, however, with the leaf miner referred to above: most if not all of the horse chestnut trees round here have this problem. --TammyMoet (talk) 15:14, 15 September 2010 (UTC)

The woodland I can see from here in Hertfordshire (mainly oak and hornbeam) is still green; only the horse chestnuts have turned brown. This year though, there is a very heavy crop of conkers, where last year there were very few. My guess is that it's due to the weather at the time of pollination. For non-British readers, the fruit of the horse chestnut tree are known here as "conkers" and until very recently were avidly collected by children for use in the sport of the same name. 109.170.169.29 (talk) 17:39, 15 September 2010 (UTC)

Cost vs. Abundance of elements

Why is silver generally perceived as a valuable expensive metal, while mercury, which is almost equally abundant, is not considered valuable or expensive? I never hear of the great expense of mercury compounds. --Chemicalinterest (talk) 14:33, 15 September 2010 (UTC)

Well in economics, there is supply and demand (in simplest terms). As you state that supply is nearly equal, then the what is driving the price of silver higher then mercury is demand. To compare, it isn't really surprising that this is the case, especially since silver has been used as a coinage metal from ancient times until the mid 20th century. Googlemeister (talk) 15:14, 15 September 2010 (UTC)

Since you're talking about perception, it's because you can't make precious jewelry out of mercury. Most people have no idea what mercury costs. I certainly didn't but just calculated that it's around USD 0.60 per troy ounce, compared to around $20 for silver. --Sean 15:17, 15 September 2010 (UTC)

See Abundance of elements in Earth's crust for the abundance of the elements. --Chemicalinterest (talk) 15:40, 15 September 2010 (UTC)

I did, but don't see its relevance to my comment. --Sean 16:11, 15 September 2010 (UTC)

It only shows the placing of silver vs. mercury on the chart. It has nothing to do with your response in particular, just to show why I asked the question. --Chemicalinterest (talk) 19:56, 15 September 2010 (UTC)

The total abundance in the Earth's crust isn't the only factor in determining the cost of a metal; the local concentration is far more important. (You only dig a mine where there is the richest ore.) Our article indicates that commercially-viable mercury ores contain between 0.1 and 2.5% mercury by weight — more than ten thousand times the average crustal abundance. Silver these days is usually extracted from much leaner ores, generally from the tailings of other mineral ores (copper or lead, often) &dmash; the richest (known) silver veins have been mostly mined out.

The purification of metal from its compounds or alloys as mined can also vary quite a bit in cost. Mercury is liberated from cinnabar through straightforward heating in air. Silver refining requires electrochemical cells (from copper ore) or the Parkes process (from lead ore). Previous silver extraction methods used mercury as part of the process (see pan amalgamation, patio process); these processes typically consumed more mercury (by weight) than they returned in silver.

The commercial price is also going to depend heavily on demand; silver has more industrial and financial (coinage, reserve metal) applications than mercury. Poorer-quality deposits of silver will be mined (and less cost-effective recovery tolerated) because we need the metal. Mercury has fewer applications, and (because of its inherent toxicity and heavy regulation in the developed world) industrial users attempt to avoid it wherever possible. TenOfAllTrades(talk) 16:23, 15 September 2010 (UTC)

On a similar vein, I could go make an unique piece of artwork. Supply is 1. But since I am a lousy artist, demand is essentially 0 (I suppose someone might need some kindling for their fireplace), so my artwork is just about worthless. Googlemeister (talk) 13:50, 16 September 2010 (UTC)

I suppose there is a tenuous link there but I don't think comparing art to mining resources is really answering the question. Spoonfulsofsheep (talk) 16:00, 16 September 2010 (UTC)

It is a demonstration that low supply does not automatically translate to high price. Googlemeister (talk) 16:17, 16 September 2010 (UTC)

Your example was high supply and low demand :-) edit: I just got what you were saying, are you being abstract or am I just tired? Spoonfulsofsheep (talk) 17:28, 16 September 2010 (UTC)

The purity of metals often affects its price, as for example silver often comes in alloys. Zinc is another good example of a significant effect of purity on price. ~AH1^(TCU) 21:59, 17 September 2010 (UTC)

Bonding with the Rocket

If I went to the Science Museum in London, briefly stroked Stephenson's Rocket with my fingertip, and then licked my finger, how many molecules of it would I ingest? Thanks 92.15.9.53 (talk) 16:45, 15 September 2010 (UTC)

You will probably brush off some iron oxides (supposing it is made of iron) quite easily. For example, rub a coin in your fingers and the fingers have a metallic smell, especially if they are sweaty. So you might rub off quite a lot. It probably will not get down the esophagus though; it will just stay on the tongue. If this is a serious question. --Chemicalinterest (talk) 16:51, 15 September 2010 (UTC)

The metallic smell on your fingers is not brushed-off metal, but your own sweat after having been broken down by the metals, according to some Ig Nobel-worthy new research. --Sean 21:13, 15 September 2010 (UTC)

Perhaps it is, but I am sure Chemicalinterest is right; iron oxide is very flaky and comes off easily. --The High Fin Sperm Whale 22:21, 15 September 2010 (UTC)

If I ran a museum, I'd hire guards with bats at every exhibit that would swat people who try to touch it. ;) Vespine (talk) 22:45, 15 September 2010 (UTC)

About the sweat broken down by metals... really? I thought the various chemicals in the sweat broke down the metal oxides on the surface. Hmm. --Chemicalinterest (talk) 11:48, 16 September 2010 (UTC)

In the article is a picture of a replica of the Rocket in its original condition; as you can see, the boiler is covered with wood and this and most other parts of the locomotive are painted. From the pictures showing its preserved condition (with the wood covering removed) I can't tell whether there is now any paint on it or not, but the assumption that all the parts are bare metal may not be correct. Certainly not all of them are iron, in any case. --Anonymous, 12:31 UTC, September 16, 2010.

No numbers at all? This was the kind of problem I would be given to estimate as a schoolboy. I suppose the first step would be estimating the volume of metal my finger would remove, and the next would be estimating the number of molecules in it. 92.15.2.221 (talk) 10:57, 17 September 2010 (UTC)

It should be possible to estimate how much shoe 'leather' is removed with each step, then estimate how the wear from taking a step compares with the wear from a finger-stroke, and how much material would be removed from iron rather than shoe-leather. The latter may relate to its different hardness. 92.29.118.215 (talk) 20:27, 17 September 2010 (UTC)

Lets say that you'd lose 0.5cm or 0.005m of shoe leather if you wore the same pair of shoes all day for three months. A NHS webpage says that people do 3000 to 4000 steps per day, so take the average as 3500. That works out at one step removing 0.000000015m. Assuming that the unit-area friction from the stroke of a finger is the same as that from one step, then with a finger-tip area of one squared centimetre, a volume of 0.0000000000015 cubic metres would be removed.

The Mohs scale article implies that a finger nail has an absolute hardness of about 6, and that iron has an absolute hardness of 21. Assume that shoe leather has the same hardness as a finger-nail. Assume that the amount of wear is inversly proportional to absolute hardness, then there would be three and a half times less wear for iron than shoe leather.

So the estimate for the amount of metal removed by stroking the Rocket with a finger-tip would be 0.0000000000015 divided by 3.5, ie 0.00000000000043 cubic metres.

How many molecules of iron are there in 0.00000000000043 cubic metres of it? I estimate that only half of them would be ingested by licking the finger. 92.28.255.54 (talk) 14:02, 18 September 2010 (UTC)

According to an reply below, there would be about 8.5 × 10^28 iron atoms per cubic metre. That figure times the volume gives 3.65 x 10^16, of which I estimate I wiould ingest half, or 1.8 x 10^16 iron atoms - a huge number. Many of them would I presume be absorbed into my blood and other tissue. 92.15.24.80 (talk) 18:08, 18 September 2010 (UTC)

Don't fuel up on days with poor air quality?

I've heard that you shouldn't get gas on "red" days, or days where it's very hot and there's poor air quality. Why is this? —Preceding unsigned comment added by 208.22.79.251 (talk) 18:01, 15 September 2010 (UTC)

Because the gas vapor that inevitably escapes when you fuel up causes the air quality to be worse. VOCs (like gas) cause ozone and smog. Ariel. (talk) 18:07, 15 September 2010 (UTC)

The theory is that gas is less dense on hot days. So, you buy less gas per gallon. This has been tested by Consumer Reports and there are issues that are not considered with the theory. First, underground tanks are insulated, so when warm gas is put in the tank, it stays warm. Second, the density difference is trivial. So, you won't notice any true savings. -- kainaw™ 18:12, 15 September 2010 (UTC)

Of course, merely driving to the gas station and back causes the car to release its exhaust pollutants into the local atmosphere, and if everybody was encouraged to fuel up on smoggy days then the smog gets worse. ~AH1^(TCU) 21:56, 17 September 2010 (UTC)

Should you let your engine warm up on cold mornings? Why?

When I was in highschool, my dad told me to let my engine "warm up" for a few minutes in the winter before I drove it. What's the reasoning? —Preceding unsigned comment added by 208.22.79.251 (talk) 18:09, 15 September 2010 (UTC)

Engines are designed to run warm (actually hot). A cold engine is not as efficient as a warm engine. There is also risk of excessive wear when the oil is not warm. In much older engines, there was a choke to adjust for the inefficiency of a cold engine. The choke is now a computer-controlled optimization. So, the computer attempts to make the engine efficient regardless of temperature. In all cars I've owned, you can tell when it shifts from "cold" to "warm" state because the idling engine will suddenly slow down. -- kainaw™ 18:15, 15 September 2010 (UTC)

If the idling engine "suddenly slows down", it's not a very good computer optimization – it sounds exactly like what happens when I release the manual choke on my car! Physchim62 (talk) 18:38, 15 September 2010 (UTC)

I'm almost positive that we've had this question multiple times before. An enterprising individual might want to sift the Ref Desk archives.... TenOfAllTrades(talk) 18:24, 15 September 2010 (UTC)

I did search the archives. The consensus is that in modern cars, the car automatically adjusts for the cold engine by using more fuel. The primary concern is engine stall. If your engine doesn't stall, it is warm enough. The minor concern is cold oil. Most people will never notice a little extra wear on the engine. -- kainaw™ 18:44, 15 September 2010 (UTC)

It's to annoy your neighbours with the sound of a pointlessly running engine. 92.29.116.58 (talk) 18:36, 15 September 2010 (UTC)

You don't have to do that anymore. You did with old cars, but it's unnecessary with more recent cars. It does drive better when warm, but driving the car does a perfectly fine job of warming it up. Ariel. (talk) 18:37, 15 September 2010 (UTC)

I have a new car and it has a light to say it has not warmed up, the instruction books says take care and dont go mad until the light has gone out, which only takes a few minutes. MilborneOne (talk) 18:49, 15 September 2010 (UTC)

I drive a 24-year old car with a manual choke. If the choke is in (as when you start it), the maximum power is lower; but for most people that's not an issue, because you don't need maximum power during the first few minutes of driving. I only notice it if I forget to take the choke out and then wonder why I can't overtake someone on the open road! Physchim62 (talk) 19:16, 15 September 2010 (UTC)

Another thought is that since you don't have to be in the car as it warms up, part of the reason would be to let the coolant temp heat up enough to let you run the heater on a freezing cold morning! Arakunem^Talk 19:48, 15 September 2010 (UTC)

Yes, I think it's so the heaters will work. They take like 30-90 seconds to start working.--92.251.241.222 (talk) 21:01, 15 September 2010 (UTC)

The cabin heater operates by taking heat from the engine coolant. It takes longer than 90 seconds to heat the coolant sufficiently that the thermostat opens and allows hot coolant to flow out of the engine itself into the heat exchanger attached to the cabin heater. Dolphin (t) 03:35, 17 September 2010 (UTC)

My understanding (though I may be mistaken) was that back in the day of single-grade motor oil, you wanted to be very gentle on the engine until it reached its operating temperature, as a motor oil with appropriate performance at operating temperatures did not adequately lubricate the engine when cold. With modern engines and multi-grade (e.g. "10W-30") engine oils, poor cold-start performance is now longer a concern. -- 140.142.20.229 (talk) 00:15, 16 September 2010 (UTC)

Define "cold". In some climates, such as central North America (Minnesota, etc.), it gets cold enough that people use Block heaters to actually get the oil warm enough to allow the engine to start. If you live in a place where the engine will start in cold weather, then the answer is, for modern cars, there's no need to start them early. However, there are some places where cars simply won't start reliably even with modern, bigrade oils. --Jayron32 02:35, 16 September 2010 (UTC)

Yeah, the "sweeping generalization" bothers me, too. If it's below zero (F), any moisture that I bring into the car (damp hair, a few snowflakes, or just plain exhaling) will not just condense onto the inside of the windshield, but will freeze onto it, which you can't just wipe off with your sleeve.

In such conditions, I think it is FAR safer to let the engine warm up until the defroster (hmm, do they still call it that?) is capable of doing its job. DaHorsesMouth (talk) 22:29, 16 September 2010 (UTC)

frying ginger -- a reverse aldol addition?

The article for gingerol says it gets transformed to zingerone when cooked. I'm amazed, because I thought caramelization and the Maillard reaction were the primary cooking reactions (other than denaturing proteins, etc.), maybe with pyrolysis or scorching being the unwanted reactions.

Is zingerone really the primary product? What about boiling (in a soup) versus frying?

Why should high temperatures in oil favour the production of zingerone? I mean, if I'm frying in 200C hot oil, shouldn't I get a dehydration product (a Michael acceptor?). Plus if I fry it in the presence of proteins or sugars (like I often do with meat), I don't think I'll get zingerone as the primary transformation product. On the contrary, I think I'll get amino-substituted or glycation products.

Plus, I didn't even think I had the harsh pH conditions to do a retroaldol reaction. If I add buffer that maintained the pH of the pan at around 7, would this reaction occur? John Riemann Soong (talk) 19:33, 15 September 2010 (UTC)

I don't see a ref for the reaction in question in either the reactant or product article. Totally speculating here, but it could be driven by evaporation of the byproduct of the reverse reaction (hexaldehyde, bp ~119 °C) at the high temp? DMacks (talk) 19:55, 15 September 2010 (UTC)

Here's a start: DOI:10.1111/j.1745-4557.1979.tb00657.x. The retroaldol can happen simply under thermal conditions, and dehydration is another reaction that can happen under these conditions. DMacks (talk) 19:58, 15 September 2010 (UTC)

(edit conflict)This is unscientific, but I can taste the difference between ginger root (very "zingy" and quite unpleasant) and ginger that is cooked (gingerbread). It is definitely more spicy-sweet than the uncooked version. --Chemicalinterest (talk) 19:58, 15 September 2010 (UTC)

Thanks DMacks -- I forgot about the evaporation of the byproduct. On paper hexaldehyde looks bulky but thanks for reminding me it wouldn't have a BP much higher than that of water. I suspect that zingerone isn't the "major product" (although it could be the most common product) of the pyrolysis of gingerol. Now reading the articles though I wonder if a significant amount of the complex flavour that comes out of ginger (when I cook it with vegetables and meats) comes from Michael addition between sugars/proteins (or an ester, or a glycation product!) with a "zingerol dehydrate".

Btw -- do I not need very acidic or basic conditions (beyond the acids naturally contained in foods) because the ketone in gingerol acts like a general base catalyst in a six-membered ring transition state? From my study of orgo, retroaldol reactions usually occur in the presence of large amounts of base or acid -- certainly not pH conditions mild enough to eat. 20:32, 15 September 2010 (UTC)

I've been following a Chinese stir fry recipe for a long time. The prep time is usually more than the cooking time:

• Heat grated ginger and garlic in COLD oil until they become aromatic. (Takes usually like 1-2 minutes.)
• Upon the very moment the ginger/garlic can be smelled, add the stir fry vegetables (ideally bok choy or gai lan -- Western vegetables don't work well for some reason -- maybe they have reactants that are less conducive to the sort of reactions Chinese stir fry has). Stir vigourously with a huge magnetic stirbar for 15 seconds.
• Cover and let steam for 45-75 seconds.

I get a very complex taste with some of the fresh ginger taste still in there. It is much more complex than the taste of gingerbread. Or is it that the authors behind the articles of gingerol and zingerone are biased towards Western cooking styles? Do Western chefs not fry ginger as often? John Riemann Soong (talk) 20:37, 15 September 2010 (UTC)

If you don't like what the articles say, find a wp:rs and change it! --Chemicalinterest (talk) 10:55, 16 September 2010 (UTC)

On Food and Cooking would probably be the most likely place that this would be discussed in detail. I don't have my copy at the moment but will have a look in a couple of days. Smartse (talk) 12:22, 16 September 2010 (UTC)

Did ancient Egyptians know the earth was round

Did those in Ancient Egypt know the earth was spherical?Smallman12q (talk) 23:18, 15 September 2010 (UTC)

Do you have some reason for thinking our article is wrong? Looie496 (talk) 23:34, 15 September 2010 (UTC)

No...I'm merely curious if any reliable sources have attributed the Egyptians with such knowledge.Smallman12q (talk) 23:55, 15 September 2010 (UTC)

The article Spherical Earth states: "The concept of a spherical Earth dates back to ancient Greek philosophy from around the 6th century BC", and talks about how ancient Mesopotamia viewed it as a flat disk floating in the ocean. No mention of ancient Egypt, though. -- 140.142.20.229 (talk) 00:05, 16 September 2010 (UTC)

Hit submit too soon. The article Flat Earth states: "In early Egyptian and Mesopotamian thought the world was portrayed as a flat disk floating in the ocean," with a reference to a book specifically for the Egyptian view. -- 140.142.20.229 (talk) 00:07, 16 September 2010 (UTC)

If Ancient Egypt lasted until 31 BC, as the page about it says, it included the Ptolemaic dynasty era, during which time Egyptian astronomy merged with Greek astronomy, with the Egyptian city of Alexandria becoming the center of scientific activity of the ancient Western world. Eratosthenes was a Hellenistic Egyptian. To scholars at the Library of Alexandria, at least, the idea that the world was a sphere seems to have been obvious. One could argue that the Ptolemaic era was not the same as "ancient Egypt", but it was certainly in ancient times, which is usually taken to include the Roman Empire. Pfly (talk) 00:29, 16 September 2010 (UTC)

Or more properly, Greco-Roman times are more properly termed the classical era, which depending on which historian you ask, may be a subset of the ancient era, or a distinct era from it. Egypt was around a LONG time. What egyptian culture believed about the shape of the world was likely to be very different from Narmer's time to Cleopatra's. --Jayron32 02:31, 16 September 2010 (UTC)

Egyptian_mythology#Cosmology says that in traditional Ancient Egyptian mythology, the Earth was pretty decidedly flat. This is different than saying, "did anyone in the spatial-temporal location we call 'Ancient Egypt' know/think the Earth was round," of course. But I think it is probably more to the point of what you are asking. I've seen, though I cannot recall where or if it was a good source (this is not an area I know much about, I'm afraid), that one of the reasons it is suggested that the Egyptians felt this way had to do with the geography of the Nile River Valley, or something along those lines. (It might have been an argument that the only places that had strong flat-earth cosmologies were places like the Nile River Valley — equatorial, relatively flat, non-sea faring, something like that). Anyway, my memory is pretty hazy on this. --Mr.98 (talk) 03:23, 16 September 2010 (UTC)

Eratosthenes, who was already mentioned, was the (Ptolemaic) Egyptian who not only was the first to calculate the circumference of the Earth (which presumes an understanding that it was spherical), but even may have fairly accurately calculated the distance from the Earth to the Sun. So "Egyptians" at least ought to be credited as the first to rationally demonstrate the Earth's shape (more or less), even if "Ancient Egypt" had existed for a very long time already before that happened (during which time all sorts of things were believed, I'm sure). WikiDao ☯ (talk) 06:35, 16 September 2010 (UTC)

It really depends in the end what is meant by the question, in the end. I just found it kind of odd that everyone was going out of their way to find examples of an "Ancient Egyptian" or two who felt to the contrary, rather than the larger evidence that their religious mythology was pretty explicitly one with a flat earth. --Mr.98 (talk) 23:40, 16 September 2010 (UTC)

The question was "Did those in Ancient Egypt know the earth was spherical?". Given the existence of Ancient Egyptian mathematicians who worked on problems that would only be pondered if they assumed the Earth was spherical, the answer seems clearly 'yes'. That the mythology talks about a flat Earth only tells us that a flat Earth featured in their mythology: it is certainly likely that very early Ancient Egyptians believed the Earth to be flat. It's also possible that uneducated Ancient Egyptians over the whole period assumed the Earth to be flat. But educated Ancient Egyptians should be as likely to know about a spherical Earth as any other educated person in the ancient world. Should a 50th century histoian assume that people in Christian Europe didn't know about a spherical Earth, based on their mythology? 86.164.78.91 (talk) 00:51, 17 September 2010 (UTC)

If their mythology was a state religion, then potentially, yes, that might be a useful answer, especially if practically nobody was "educated" along the lines you are implying (except for many a handful of the top elite), and their society lacked anything like a collective "scientific understanding". It is not like the Egyptian mythology/religion was some causal thing that people did on Sundays. Anyway, either way, pointing out that the primary religious system was a flat earth would be completely relevant, indeed. Probably more so than pointing out the one or two scholars who we know thought otherwise, without any knowledge as to whether their views were known to others. I think assuming a "modern" level of common understanding (or even interest) in scholarly work is pretty absurd for the periods you are talking about. --Mr.98 (talk) 01:16, 17 September 2010 (UTC)

If the question is about common understanding, then sure, it's unlikely that most Egyptians of ancient times knew the Earth was a sphere. For most the shape of the Earth was probably a non-issue. On the other hand, the original poster was curious about sources, and it seems highly unlikely that there are any sources about what the average common person in ancient Egypt thought about the shape of the Earth. Pfly (talk) 07:57, 17 September 2010 (UTC)

I'm not really concerned with what the common person knew...that would be quite difficult to determine and people today also don't have the time to determine if its spherical. Rather, I'd like to know if there were any notable mathematicians, or other individuals who theorized that the earth was spherical.Smallman12q (talk) 12:13, 17 September 2010 (UTC)