Wikipedia:Reference desk/Archives/Science/2010 December 26

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December 26

Fog

What would happen if you boiled fog machine liquid? Would it make a load of fog? 82.44.55.25 (talk) 00:23, 26 December 2010 (UTC)

I know of two types of fog machines, one basically does boil water, so nothing would change. The other uses dry ice (frozen carbon dioxide), which goes directly from a solid to a gas, with no liquid in between (it sublimates). It's not possible to boil carbon dioxide at normal atmospheric pressure. If you pressurized it and heated it, you might get a liquid, and if you suddenly released the pressure, you might get a lot of "fog". StuRat (talk) 04:02, 26 December 2010 (UTC)

I am confused when you say "nothing would change". Do you mean nothing would change with the fog liquid if I boiled it and it would just sit there in the pot, or do you mean there's no difference between whatever a fog machine does to the liquid and just boiling it, so it would make fog? And I'm specificlly talking fog machine liquid, not dry ice. 82.44.55.25 (talk) 10:45, 26 December 2010 (UTC)

From fog machines Typically, fog is created by vapourizing proprietary water and glycol-based or glycerine-based fluids or through the atomization of mineral oil. I don't think boiling would vapourize it particularly effectively, I don't think you'd get a LOT of fog. Vespine (talk) 13:05, 26 December 2010 (UTC)

How about dropping dry ice into boiling water? ~AH1^(TCU) 17:43, 27 December 2010 (UTC)

What is the scientific term for levels of activity by time of day?

An organism is diurnal if it is active during the day, nocturnal if active during the night, etc, but what is the formal term for nocturnality and diurnality themselves? Is there a scientific word meaning "the level of activity of an organism by time of day" that includes diurnality, nocturnality, crepuscularity and all other variants on the concept? I've been wondering this for a long time but haven't been able to find this term despite a hard search. Circadian rhythm seems to be the most closely related concept that I've found, but it seems to be a bit broader than just activity levels. Abyssal (talk) 04:11, 26 December 2010 (UTC)

Chronotype? Clarityfiend (talk) 04:34, 26 December 2010 (UTC)

I don't think that's exactly what I'm looking for. That concept seems to be behavioral, like if a person (a diurnal animal) is a "night owl" (ie chooses to adopt different behavior). I'm more interested in activity levels innate to a species. Abyssal (talk) 07:24, 26 December 2010 (UTC)

Circadian? SpinningSpark 16:22, 26 December 2010 (UTC)

"The time during which an organism is normally active is referred to as the subjective day" - from Pace-Schott & Hobson (2002). NRN. 3, 591–605. Is this what you are referring to? --Mark PEA (talk) 21:39, 26 December 2010 (UTC)

Solar sails

Why aren't solar sails used to propel all spacecrafts? Since they don't require any energy other than to deploy and retract the sails, wouldn't they free up space that would've been used to carry fuel? --75.28.52.27 (talk) 20:31, 26 December 2010 (UTC)

They are difficult to make and deploy, take a long time to build up speed 82.44.55.25 (talk) 20:38, 26 December 2010 (UTC)

"Minimize total energy consumption" is only one objective during spacecraft engineering. While it is true that a solar sail will reduce the energy consumption, and consequently the mass of chemical propellant, a solar sail may incur other costs. Those costs compete against other design objectives - such as "minimize total flight-time"; "minimize flight-mass;" "minimize flight volume;" "minimize risk of failure;" "minimize monetary cost of spacecraft;" and "test specific scientific or engineering design." (With some imagination, you can expand that list ad nauseum). The point is, when you think of spacecraft design, you always have to keep yourself in the mindset of engineering tradeoffs and cost-benefit analysis. With present technology, even though solar sails might reduce the total mass of the propulsion system, they may significantly increase the flight-time - which is usually a tradeoff that the space-flight program cannot afford (because it affects the science objectives, the spacecraft design, and the dollar-budget). They may also introduce signficant risk - because they are both less-tested and less-controllable than a chemical rocket propulsion system. The chance that the propulsion system could underperform (or fail altogether) is altogether unacceptable, and generally outweighs any cost, mass, or other benefit that a solar-sail might provide. You might be interested in reading through the Lecture Notes for AA 222 - Multidisciplinary Design Optimization (a graduate course in spacecraft design from Stanford); you can learn how an aerospace engineer will formally specify the design requirements, evaluate various technologies, and plan the spacecraft. We also have the less-technical spacecraft design article, which mostly just links to articles about related subfields of engineering. Nimur (talk) 20:54, 26 December 2010 (UTC)

To date, Solar sails (skim the article, it's informative) are a basically untested technology. There has been a grand total of one spacecraft to successfully deploy a solar sail and use it for acceleration: IKAROS (Here's a news article about IKAROS, showing the sail). And it's only been up for about 6 months. If it successfully reaches Venus, and there are no major problems with the sail, other solar sail-equipped spacecraft may begin to appear; it's claimed in the IKAROS article that Jupiter is the planned next destination for a JAXA solar sail if this one works out. It's hard to find what exactly IKAROS is carrying (unfortunately, the IKAROS official website is woefully incomplete), but it appears that it's not accelerated solely by the sail: it also accelerates using an Ion thruster. I think it's safe to say that solar sails have a few years to go before becoming common on spacecraft.

It's interesting to note that ion thrusters, now pretty common on interplanetary spacecraft, were not really used in spacecraft propulsion until Deep Space 1, launched in 1998 (ignoring the SERT-1 probe, where one ion engine only ran half an hour, and the other one failed). If solar sails improve at a pace similar to ion thrusters, we may be seeing solar sails used fairly frequently in 20 years. Buddy431 (talk) 22:28, 26 December 2010 (UTC)

After the Japanese Spacecraft IKAROS the idea becomes more accepted. The Jupiter mission will be a lot of fun to see. The talks at COSPAR Bremen showed that JAXA has plans for the solar sail. By the way IKAROS do not use the sail to get faster they use it as a break! It is more efficient close to the sun and getting to venus or mercury are the best places to demonstrate the capabilities. The fact that IKAROS is going to Venus was not because of that, but simply it was the only mission which was launched at the right time with a piggyback capability.--Stone (talk) 22:49, 26 December 2010 (UTC)

Using the solar sale "as a brake" is essentially equivalent to using it to speed up; in space, it's the total acceleration (Delta-v) that's important, not which direction it's in. Buddy431 (talk) 23:14, 26 December 2010 (UTC)

Don't buy your solar sail on sale, or you may find it breaks when it brakes. StuRat (talk) 03:43, 27 December 2010 (UTC)

has any famous scientist ever expressed doubts about the moon landing authenticity?

bertrand russell, a very famous mathematician and philosopher, expressed doubts about the official jfk assassination story. did any famous scientists (like feynman, etc) ever express doubts about the authenticity of the moon landings? 87.91.6.33 (talk) 22:34, 26 December 2010 (UTC)

Why would they? It happened. The moon landings involved tens of thousands of people. Keeping that many people silent on a cover up for 40 years would be impossible. Wikileaks has shown us how keen some government employees are to tell the truth and release embarrassing information to the public. And I'm writing this as an Australian. The landings depended on people on around the world, including Australia, for communication. (Have you seen The Dish?) There would have been hundreds here involved. Nope. we wouldn't have kept America's secret, if there was one. HiLo48 (talk) 22:44, 26 December 2010 (UTC)

There are for sure some very old and very famous scientist expressing doubts about anything. The percentage of expressed stupid thoughts is not smaller because you are a scientist.--Stone (talk) 22:54, 26 December 2010 (UTC)

I would expect scientists to say stupid things less often than members of the general population. It's not never, but I would hope it's less frequent. Of course, they can do a lot more damage when they say stupid things because they have greater credibility (even if their area of expertise is completely unrelated to what they are talking about). --Tango (talk) 23:23, 26 December 2010 (UTC)

I didn't ask about old scientists but famous ones, like Feynman. So, did any famous scientist ever express doubts? 87.91.6.33 (talk) 23:49, 26 December 2010 (UTC)

Charles K. Johnson, president of the International Flat Earth Research Society declared that NASA faked the landings, which were staged by Hollywood with Walt Disney sponsorship and based on a script by Arthur C. Clarke and directed by Stanley Kubrick. The first link attests to Johnson being famous enough to be noted in Wikipedia and the second link is a report about Johnson in Science digest July 1980. Together these links establish Johnson as a Famous Scientist. Cuddlyable3 (talk) 23:52, 26 December 2010 (UTC)

I'm sorry, but calling Johnson a scientist on the basis of the fact that he was featured on a website called Science Digest (which isn't a scientific periodical at all) is utter, total, and unadulterated nonsense. --Mr.98 (talk) 01:37, 27 December 2010 (UTC)

Calling Charles Johnson a scientist can only be construed as a joke. His belief on flat Earth alone is enough to doubt about his mental health.Quest09 (talk) 12:19, 27 December 2010 (UTC)

I would hope so, but in my experience CL3 has had some difficult distinguishing nonsense from sense on the web before. I suspect that his or her above post was made in complete earnestness. I'd love to be wrong, though. --Mr.98 (talk) 19:51, 27 December 2010 (UTC)

Another issue is, what kind of scientist? Would the comments of a famous medical scientist mean anything on moon landings? Scientists are specialists. HiLo48 (talk) 23:54, 26 December 2010 (UTC)

WP:OR - The first time I ever met Doug Osheroff, he explained how after winning his Nobel prize for superfluid helium, all kinds of media and political people would call him up to ask his opinion about stem-cell research and space-shuttle disasters and junk. (Somehow even NASA thought he was "expert enough" about Space Shuttles)! But he was only really an expert on helium! He said, as a prestigious scientist, the public automatically trusted him to be an expert on everything scientific, all the time - which was really very silly, and demonstrated how little the public actually understood modern science. The second time I met Doug Osheroff, I didn't get to talk to him very much, but I did get to yell at him because he walked through our "DANGER DO NOT ENTER" barrier at the back parking lot behind the physics building, right into the path of our rocket pyro test (he was just trying to take a shortcut to his car, and delayed our entire procedure). He saw our sign and caution-tape, but he said he "didn't think it would be very dangerous." I guess my point is that even very smart and famous scientists can say stupid things; and you shouldn't always trust their judgement. Nimur (talk) 23:57, 26 December 2010 (UTC)

You just made a preemptive strike against something no one has shown. If you don't think it would be relevant for someone with a Nobel Prize in helium to express doubts about the space missions, you have that right. But me, I care a lot about whether in fact anybody like that did. Your response is like me asking "has any president been antisemitic?" and you saying: what if they were - that doesn't prove that Jews are bad! A president can be very wrong, why Nixon was a crook who would have gone to prison but for a presidential pardon from his successor!!! Why even ask that question??? head asplode. 87.91.6.33 (talk) 00:27, 27 December 2010 (UTC)

I'm sorry. Allow me to clarify. Out of all the famous scientists that I know, none has ever expressed doubt to me about the veracity of the manned moon landings. Nimur (talk) 00:43, 27 December 2010 (UTC)

There's a list of people at Moon_landing_conspiracy_theories#Hoax_proponents_and_their_proposals, some of who are scientists. 82.44.55.25 (talk) 00:52, 27 December 2010 (UTC)

Yes, there's a list of people, but only one of them appears to qualify as being a scientist - Alexander Popov - described as a Soviet physicist and inventor with the degree of Doctor of Physical-Mathematical Sciences. Dolphin (t) 01:16, 27 December 2010 (UTC)

And his area of specialisation appears to be around light - lasers, spectroscopy, etc, so hardly an expert on flying people to the moon. HiLo48 (talk) 02:15, 27 December 2010 (UTC)

Are there any scientists whos field of expertise is "flying people to the moon"? I always assumed the teams of scientists who do these kinds of things have a vast array of different areas of expertise which they apply to the task at hand... 82.44.55.25 (talk) 11:04, 27 December 2010 (UTC)

The evidence available on Wikipedia is very comprehensive regarding high-profile people known to believe the manned moon landings didn't occur. That evidence indicates that no scientist whose field of expertise is directly relevant to manned moon landing believes NASA's manned moon landings were hoaxes expresses doubt about the authenticity of these landings. Dolphin (t) 12:27, 27 December 2010 (UTC)

Thank you, although you switcheroo "none of them express doubt" into "none of them believe it is a hoax". I will accept your answer as really reading as the former. (Since there are, in fact, many reasons one could doubt something without expressing it publicly). Thank you. 87.91.6.33 (talk) 15:19, 27 December 2010 (UTC)

There was nothing significant in my choice of words. I have struck the original words and replaced with words closer to the original question. Dolphin (t) 07:15, 28 December 2010 (UTC)

You're right, of course. In fact the Apollo program was used a great example of excellent project management for the way it brought together the diverse resources it required. The points made above about specialisations among scientists were simplifications, but still relevant. HiLo48 (talk) 11:22, 27 December 2010 (UTC)

In the case of Popov, he would be an expert for the purposes of evaluating moon landing hoax claims if those claims were based on evidence generated through laser spectroscopy. His pet conspiracy preference, however, revolves around the notion that the launches were faked using Saturn 1B rockets disguised as the (much larger and putatively non-existent) Saturn V. Leaving aside the political propaganda angle (Soviet scientist denies American accomplishment during Cold War, film at eleven), he might be a credible source on this question if he had a background in military reconnaissance, remote imaging, and aerospace engineering. Because his conclusions are based on matters far outside his own specialty, he should be taken as no more credible than any other randomly-picked clever-but-gullible individual. The fact that his day job is as a 'scientist' isn't helpful here, any more than being a 'doctor' is sufficient if a dermatologist were to tell you that you needed heart surgery. TenOfAllTrades(talk) 15:06, 27 December 2010 (UTC)

If my dermatologist were to tell me he strongly suspects I have a heart problem, I would take it seriously! A lot more seriously than if Aunt Em did. 87.91.6.33 (talk) 15:24, 27 December 2010 (UTC)

Speaking of switcheroos, I see what you did with my words there, and it was rather sketchy. I said "heart surgery" not some generic "heart problem". In most places, a dermatologist is a full medical doctor, but one who has additional specialist training. (The same is true of cardiologists and cardiac or cardiothoracic surgeons, albeit with a very different sort of specialization.) I would expect a dermatologist to capable of detecting certain overt types of heart conditions (and indeed, some conditions are associated with specific dermatologic markers) — but it wouldn't be appropriate or expected or credible for a dermatologist to authoritatively prescribe cardiac surgery. TenOfAllTrades(talk) 17:47, 27 December 2010 (UTC)