Wikipedia:Reference desk/Archives/Science/2019 November 29

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November 29

Pluto

The description of this image of Pluto (right, top) on Wikimedia Commons says:

This is the clearest view yet of the distant planet Pluto and its moon, Charon, as revealed by NASA's Hubble Space Telescope (HST). The image was taken by the European Space Agency's Faint Object Camera on February 21, 1994 when the planet was 2.6 billion miles (4.4 billion kilometers) from Earth; or nearly 30 times the separation between Earth and the sun.

If it's the clearest view yet, then where did the second image (right, bottom) come from? Or is it because the description is apparently from 1998 and hasn't been updated since then? JIP | Talk 14:09, 29 November 2019 (UTC)

New Horizons. "New Horizons" Pluto.—eric 14:51, 29 November 2019 (UTC)

Thanks. So why does the description of the first image say "This is the clearest view yet of the distant planet Pluto" when the New Horizons image is clearly clearer (pun intended)? JIP | Talk 14:55, 29 November 2019 (UTC)

It also goes on to say"...and its moon, Charon" May I suggest that the first image is that of Charon. Though the top image resembles neither, and the appropriate moon article has a better picture. Another option is that the first image is mislabelled. Anton 81.131.40.58 (talk) 15:02, 29 November 2019 (UTC)

copied from JPL's description. It's pluto.—eric 15:07, 29 November 2019 (UTC)

Also the description needs to be updated as Pluto is no longer considered a planet. It is a dwarf planet. Dja1979 (talk) 15:37, 29 November 2019 (UTC)

(ec) Check the description on commons (eric's first link): The image was created in 1998, uploaded to en.wikipedia in 2008, transferred to commons last week, obviously without changing the text, which was accurate in 1998 and 2008, but not any more. --Wrongfilter (talk) 15:38, 29 November 2019 (UTC)

I have made some updates to the 1994 picture's description. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:15, 29 November 2019 (UTC)

Apparently someone copied the caption from the NASA page, but only part of the image. The one in question does not show Charon at all, so the caption is nonsense as applied to it. Maybe the complete image is somewhere on Commons as well; I haven't searched. --76.69.116.4 (talk) 06:43, 30 November 2019 (UTC)

@JIP: Please feel invited to correct/update or mark such entries yourself right away on its own page. Worst thing that can happen is that it will be re corrected instead of drawing 20-30 people into a missplaced discussions. Please read WP:MAINT. --Kharon (talk) 08:21, 30 November 2019 (UTC)

If it was on Wikipedia rather than Commons I might, but I don't know how to call attention to such things over there. Feel free to do so yourself. --76.69.116.4 (talk) 12:06, 30 November 2019 (UTC)

So read WP:MAINT to learn how to make YOUR account on commons! We answer scientific Questions - not offer general or specific maintenance here. — Preceding unsigned comment added by Kharon (talk • contribs) 21:57, 1 December 2019 (UTC) (and the signature added by CiaPan (talk) 20:31, 2 December 2019 (UTC))

@JIP: The description at the image page File:Pluto1.JPG clearly says:

At the time this picture was taken, it was the clearest view...

and later it specifies the image was taken in 1994, whilst the other one was taken in 2018. --CiaPan (talk) 20:26, 2 December 2019 (UTC)

Fix: the second image was taken in 2015, not 2018. --CiaPan (talk) 21:05, 2 December 2019 (UTC)

The description was changed to include "At the time this picture was taken" after I posted my question. It originally just read "This is the clearest view yet". JIP | Talk 20:43, 2 December 2019 (UTC)

Yes. I changed it following the earlier comments here. If it needs further updating, let me know. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:23, 3 December 2019 (UTC)

ANS receptors

Why do Beta 2 receptors of the Sympathetic ANS relax blood vessels of the skeletal muscles but Alpha receptors also part of the Sympathetic ANS constrict the same blood vessels of the skeletal muscles? --217.97.100.184 (talk) 18:16, 29 November 2019 (UTC)

Links: adrenergic receptor, alpha-1 adrenergic receptor, alpha-2 adrenergic receptor, beta-1 adrenergic receptor, beta-2 adrenergic receptor. It looks to me from those articles that under physiological stimulus (as opposed to synthetic agonists), the effect of beta adrenergic receptors is stronger than that of alpha receptors, and so adrenergic stimulus overall causes vasodilation of blood vessels supplying skeletal muscle. Additionally, alpha-1 receptors are downregulated in muscles under stress. This causes increased vasodilation in muscles being heavily used, which shunts more blood to those muscles as opposed to inactive ones. This is likely the primary evolutionary purpose. --47.146.63.87 (talk) 07:34, 30 November 2019 (UTC)

Thank you very much! --217.97.100.184 (talk) 22:17, 30 November 2019 (UTC)

Microwaving food

I've noticed that some foods, such as rice, heat up faster in a microwave than other foods, such as meat, and end up taking all the heat while the latter remain lukewarm. Why is that so and why is cooked meat in particular so hard to rewarm? 93.136.178.2 (talk) 21:00, 29 November 2019 (UTC)

Meat is likely to be a lot more dense than rice. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:25, 29 November 2019 (UTC)

• The microwave wavelength is chosen so that it's absorbed effectively by water. Dry food isn't heated so effectively by it, nor is ice. IMHE, rice isn't heated well by a microwave. When reheating it, I always sprinkle it with some extra water.

There used to be a problem of poor energy distribution within the oven cavity, hence the turntables. But modern microwaves are much better for this.

If you make some cup-shaped icecubes specially, you can do the experiment of boiling water in an ice cube. Andy Dingley (talk) 21:30, 29 November 2019 (UTC) Edited with poster's permission. DroneB (talk) 23:47, 2 December 2019 (UTC)

Interesting, for me rice heats up the fastest, while watery food such as a soup or a stew needs the extra hard setting. Maybe my microwave has the wrong wavelength? 93.136.178.2 (talk) 21:43, 29 November 2019 (UTC)

Your soup may be gaining a lot of heat, but still staying at a low temperature. It's coupling the microwave energy in pretty well, but water also has a remarkably high specific heat capacity, thus takes a lot of energy to warm up. Andy Dingley (talk) 22:12, 29 November 2019 (UTC)

And soup is mostly water, whereas rice is mostly not (and also has lots of air pockets, so the "cup of rice" has even less heat capacity than "a grain of rice". It also depends what other ingredients are present on the rice, meat, soup. Added salt or certain other chemicals can increase microwave absorption. DMacks (talk) 22:23, 29 November 2019 (UTC)

"Added salt or certain other chemicals can increase microwave absorption. "

pmid:17249886. And "Microwave heating of alkaline or salt solutions in open or closed vessels will concentrate these solutions, causing precipitation of salts and formation of crystal deposits on vessel walls. These crystal deposits will absorb microwave energy, causing localized heating which may char and damage vessel components, leading to possible failure." from [1] to get started. [2] is too technical for me to grasp the implications at a casual read. DMacks (talk) 22:45, 29 November 2019 (UTC)

"microwaves of 2.5-20 GHz frequencies,"

Mine's 2.45GHz. So's yours. So's everyones. To get those frequencies, I have to go in the workshop and get the radar bits out. Salted water might improve absorbtion at 2.45GHz, but not crystals. Andy Dingley (talk) 22:52, 29 November 2019 (UTC)

The cem.com URL is 2.45 GHz. Sorry, I wasn't clear that the quote is from the subsequent link, not the PMID link. I don't have access to doi:10.1080/00207217908938675, but it seems like it might have useful info. I won't have time to run those sorts of controlled experiments (for example, T-vs-t plot for constant power at various [NaCl]) for a week or two. DMacks (talk) 23:00, 29 November 2019 (UTC)

More general answer: microwave ovens work primarily by heating water. Heat is transferred to the rest of the food by thermal conduction. This means foods with a higher water content get heated more quickly and evenly. This is also why microwave cooking directions often advise you to let food sit after microwaving, and sometimes to stir it between cooking stages, or to use lower power settings. This allows the heat to diffuse from the water. --47.146.63.87 (talk) 07:39, 30 November 2019 (UTC)

Good microwave ovens offer multiple automatic heating programs that use predefined heating and heat dispatching phases to warm and/or melt up food. Of course thous are more expensive than the cheapest ones and they need more time and a little more energy to achieve the task. --Kharon (talk) 08:06, 30 November 2019 (UTC)

• Please don't pass on the misinformation that microwaves only heat water or that they don't heat ice. From Microwave oven#Principles:

"Water, fat, and other substances in the food absorb energy from the microwaves... It is a common misconception that microwave ovens heat food by operating at a special resonance of water molecules in the food... Microwave heating is more efficient on liquid water than on frozen water, where the movement of molecules is more restricted... Compared to liquid water, microwave heating is less efficient on fats and sugars (which have a smaller molecular dipole moment)... However, due to the lower specific heat capacity of fats and oils and their higher vaporization temperature, they often attain much higher temperatures inside microwave ovens." --Guy Macon (talk) 08:13, 30 November 2019 (UTC)

Go boil some water in an ice cup, then come back and say that. Andy Dingley (talk) 14:11, 30 November 2019 (UTC)

Careful: "things that start off at a higher temperature wind up getting to a higher temperature" doesn't really prove a whole lot, and "liquid water gets hotter faster than ice" is actually completely consistent with what Guy just said. We are obviously not operating at equilibrium conditions. DMacks (talk) 14:43, 30 November 2019 (UTC)

I generally refrain from responding to Andy Dingley, because I have never seen him change his opinion when faced with evidence against it. For those who doubt what our Microwave oven article says ("Microwave heating is more efficient on liquid water than on frozen water, where the movement of molecules is more restricted") it is a simple matter to confirm at home that microwaves do indeed heat ice. Simply place an ice cube in a microwave, heat it on high, and see how long it takes to melt. Now repeat the experiment without turning the microwave on. It is also interesting to try dry sugar and pure cooking oil, but be careful; it is easy to make a hard-to-clean mess. And if anyone still thinks that microwaves only heat water, buy one of these [ https://www.amazon.com/dp/B01D9V8Z9O/ ], [ https://www.amazon.com/dp/B07BDK7BZY/ ] (or just read the customer reviews for them). --Guy Macon (talk) 16:58, 30 November 2019 (UTC)

Actually Guy, what you usually do is post insulting and personally targetted cartoons.[3] And a bit of pontification has always been your way. BTW - WP articles are not reliable sources. Andy Dingley (talk) 18:48, 30 November 2019 (UTC)

No but their sources should be. Nil Einne (talk) 18:42, 1 December 2019 (UTC)

Andy Dingley, explain how the dipole moment of ice differs from the dipole moment of water to make it a non-absorber of microwave radiation. Indeed, we actually find the opposite, that the dipole moment of ice is somewhat higher than the dipole moment of liquid water, but other factors reduce the thermal heating effects. Reduce, but not get rid of completely. Ice is absolutely a microwave absorber, and thus absolutely will heat in a microwave oven. --OuroborosCobra (talk) 23:26, 1 December 2019 (UTC)

Don't bother responding to Andy Dingley. I never do. Once he says that ice isn't heated by microwaves, he will never back off and admit that he was wrong. Talking to him about it is a waste of time. He is completely ineducable. The good news is that he doesn't attempt to "correct" our Microwave oven article, so the only harm is him posting false information on the reference desks.

All he has to do is put an ice cube in the microwave and heat it, then do the same with another ice cube but without turning the microwave on. Or read the sources in our article that are used for citations for the claim "Microwave heating is more efficient on liquid water than on frozen water, where the movement of molecules is more restricted"

References

I await the rather boring insult that typically follows showing Andy Dingley that he is wrong. --Guy Macon (talk) 07:07, 2 December 2019 (UTC)

• Try it for yourself, do the experiment. The OP in this thread opened with "faster", not "is not heated by". Of course ice is heated in a microwave, same as rice is, but not as effectively as liquid water is. Thus it's enough to do the (pretty common, high school science) of the "boiling water in an ice cup" demo. Much the same as boy scouts years ago used to boil water over a campfire in a cup made from folded paper. It's not a black and white, all or nothing distinction, but there is a difference. Andy Dingley (talk) 13:41, 2 December 2019 (UTC)

• "The microwave wavelength is chosen so that it's absorbed effectively by water. Dry food isn't heated by it, nor is ice." --posted by Andy Dingley on 21:30, 29 November 2019 [4], emphasis added.

--Guy Macon (talk) 15:11, 2 December 2019 (UTC)

• As a first approximation, I would still stand by that. Yes, it would be nice to cite precise numbers for everything, but that's both a lot of legwork, and also obscures what's still the basic point. Andy Dingley (talk) 15:19, 2 December 2019 (UTC)

• Which are you standing by? ice is not heated, or ice is heated, but not as effectively as water? It can't be both. Shall I quote your reply when I pointed out that Microwave oven says (with a citation) that "Microwave heating is more efficient on liquid water than on frozen water, where the movement of molecules is more restricted"? On second thought, don't bother. I see that I have been sucked into responding to you, breaking my own rule. I will now go back to letting you post false information without responding. Nothing good will come from attempting to correct your error. --Guy Macon (talk) 15:36, 2 December 2019 (UTC)

• It depends on the context, of course. People with basic conversational skills can appreciate that. It's common knowledge that a massively popular use of microwave ovens is to heat up frozen bachelor chow, straight from the freezer. So clearly "ice is heated in microwaves". And yet, that microwave oven will probably have a defrost setting on it, which runs the oven at a duty cycle of only 1/6 or so, because it is so poor at heating a frozen meal. Considerable additional time is needed to microwave cook from frozen. In fact, much of that initial heating of the ice (to defrost it, if not to make it hot) is from conduction of water around the package which has already begun to melt. This is why microwaveable meals are so much more easily cooked (and more evenly cooked) if defrosted first, before microwaving. This is why such rapid meals often include a susceptor, microwave-absorbing packaging so that they can get an "early start" on this otherwise difficult defrosting.

So yes, "ice absorbs microwaves" and yet at the same time, "You can't cook an ice cube, same way you can cook the water sat next to it". It's a subtlety and a distinction, not a contradiction. Andy Dingley (talk) 15:56, 2 December 2019 (UTC)

I recently had a disagreement with somebody who firmly believed that cast-iron was a poor conductor of heat. (It is a good conductor of heat.) That fundamental mistake is the same one AD is making. The difference is in the rate of heating of water, due to microwaves, in its liquid form, and water in its solid form. It heats faster in liquid form, but still heats up in solid form. Guy is correct. -Roxy, the PROD. . wooF 18:18, 2 December 2019 (UTC)

what an amount if useless flame. Of course Guy is right. and so is AD. The silly dispute is much of the "the glass is half full! No it is half empty!" kind, with very marginal focus on OP question Gem fr (talk) 21:13, 2 December 2019 (UTC)

• Ah yes Roxy, the one where Guy stripped out all the changes and sources, just because I'd written them and he can't abide that. Andy Dingley (talk) 22:54, 2 December 2019 (UTC)