How to Spot a Psychopath

A reader writes:

The Oatmeal recommends sites get more traffic and Facebook likes by writing an epic love story involving cage-fighting nuns and tanks, or if that is not possible, explaining why the sun and the moon appear to be the same size in the sky.

Both of these seem right up your alley, but frankly I for some reason find the second one more interesting. Why ARE the sun and moon the same size? Is it just a bizarre coincidence, or is there some astronomical orbit reason for it?

Lucas

I'm afraid it is indeed just a fluke. Which, furthermore, starts to look less amazing when you discover that the sun and moon don't actually have a particularly spooky similarity in size.

I remember reading some flaky book when I was a kid, possibly some von Däniken claptrap or other, that made much of the extraordinarily precise apparent-size match between the 0.55-Earth-diameter moon and the 109-Earth-diameters sun. Surely this cannot be mere coincidence, hence ancient astronauts and Nazi moon bases and the various Stargate series are all documentaries et cetera.

Unfortunately for these otherwise-very-plausible speculations, the sun and moon are not actually the same size in the sky. They can be, but they usually aren't.

The earth's orbit around the sun is not perfectly circular, but it's close. On average it's one astronomical unit (oddly enough), but we're closest, 0.983 AU, in early January, and furthest, 1.017 AU, in early July. The actual sun stays the same size, so from our point of view it ranges from 31.6 to 32.7 minutes of arc.

For visual learners, that's about this much of a range:

(I made this from this NASA picture depicting a gigantic magnetic filament erupting from the surface of the sun. The same filament would not, of course, be there in both January and July.)

The moon's orbit around us is more eccentric than the earth's orbit around the sun, so the moon changes in apparent size much more dramatically than the sun does. It ranges from 29.3 to 34.1 arc-minutes or, to the same scale as the above sun picture...

...this much.

(I took that moon picture myself. Residents of the northern hemisphere are invited to stand on their heads to make it look more familiar.)

(UPDATE: I forgot to mention the moon illusion when I first put this post up. Yes, the moon, and the sun too for that matter, seems bigger when it's near the horizon. No, it actually isn't. If anything, it's smaller!)

Here's the two ranges compared.

The only time when ordinary people really compare the size of the sun and moon is, of course, when there's a total solar eclipse. Then it really does look as if the moon neatly covers the entire sun, helpfully giving us a nice view of the corona, which is normally washed out by the much greater brightness of the body of the sun. (You can actually view the corona from the surface of the earth at other times, but you need special equipment to block out sky-glare.)

At this point, you may be wondering whether the roughly-month-long lunar size cycle and the year-long solar size cycle can coincide with an eclipse in such a way as to put a minimum-size moon in front of a maximum-size sun (well, any size of sun, really, there's not that much difference), so that the moon fails to completely obscure the sun.

Yes, it can; it's called an annular eclipse, and there's one coming shortly, though I won't be able to see it from here in Australia.

Here is a lot more information about all of this.

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

A reader writes:

Seeing lrwiman's comment on your post about how you can't lose weight by eating ice reminded me: Do you really need to drink eight glasses of water a day?

I guess it actually depends on who "you" are, how big or small, and how much you sweat and so on. Is eight 8-oz glasses just a one-size-fits-most amount for everyday urban humans?

Lana

There is no scientific basis for the "eight glasses a day" idea.

Eight eight-fluid-ounce glasses add up to, of course, 64 fluid ounces, or about 1.9 litres. That is rather a lot. If you're an office worker, you are very unlikely to need that much water (or equivalent other liquids, though the people who support the eight-glasses thing often say that no beverage other than water counts at all) to be perfectly hydrated. If you're a labourer in a hot climate, though, you're going to need a lot more than eight glasses.

(See also, people hiking in the desert who don't realise that you need to drink a lot more water, and keep your electrolytes up, when you're exercising in high temperatures and low humidity.)

Unless you drink a really amazingly large amount, it won't do you any harm to drink more water than you need, if you're not concerned about the amount of time you spend in the bathroom. 1.9 litres over several hours is well below the level needed to cause water intoxication in an adult, unless your kidneys are in bad shape.

Note that your total water intake can very easily be three or four litres a day, because other beverages, and water contained in food, count towards it as well. The eight-glasses people usually warn against consuming water when it's mixed with other substances that reduce its net hydrating effect, like caffeine or alcohol, which are both diuretics.

As usual, though, the dose makes the poison, or in this case the diuretic. A doppio ristretto or shot of Polish Pure Spirit is, like drinking seawater, going to have a net negative effect on your hydration. But if ordinary black tea didn't hydrate you, the entire British Empire would have died of thirst in about 1750. You can also remain well hydrated if all you drink is beer or weak wine; beer and diluted wine used to be staple beverages for whole cultures before the invention of sewer systems, when the available water was commonly contaminated with organisms that couldn't survive a few per cent of ethanol.

Drinking lots of water, often but not always this particular figure of eight glasses a day, pops up quite often as part of odd diet regimes.

The "Stillman diet", for instance, was an early low-carbohydrate diet which prescribed eight glasses of water a day in addition to any other fluid intake. And it sure did seem to pare away the pounds; it made a significant contribution to Karen Carpenter's downward trajectory of both weight and health.

Lorraine Day includes a lot of water-drinking in her list of things you can do to, immensely plausibly, cure yourself of cancer (unless of course you are Jewish, in which case she'd probably prefer that you die).

Back here on planet Earth, drinking water when you feel peckish can be a good dieting trick. Go ahead and throw in some ice cubes too, if you want something to (carefully...) chew on.

But apart from this, and from a few diseases for which drinking a lot of water is a treatment, there's no reason to drink water when you're not thirsty.

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

A reader writes:

How dangerous is second-hand smoke, really?

The bans on indoor smoking that've taken over the Western world suggest that it's REALLY dangerous. Here in Australia you can no longer smoke even in a pub, so apparently second-hand smoke is worse for you than alcohol.

But it stands to reason that second-hand smoke is much more dilute than the smoke sucked out of the actual cigarette. I can believe it'd be a big health hazard if you were in some 1925 basement speakeasy jazz club with no ventilation and everyone smoking like crazy until you could barely see your hand in front of your face, but the thickness of smoke in a pub before the ban wasn't anything like that. It still made your clothes and hair smell like an ashtray, but that's just disgusting, not dangerous. Was it really that bad?

Richelle

Nobody knows exactly how dangerous second-hand smoke, or "passive smoking", is.

This is partly because of the, well, smoke screens, produced by astroturf organisations with the usual hilarious Decent People Opposed to the Decapitation of Adorable Ducklings names and the similarly usual giant piles of funding from the tobacco companies.

But it's also partly because there is, as you say, such a wide range of possible exposure levels.

And, I think, it's mainly because this is principally an epidemiological question, and epidemiology is a slippery area of study.

Given all these caveats, though, it's still clear, from numerous studies, that chronic exposure to second-hand smoke, even at relatively low levels, does significantly increase the chance of a non-smoker getting lung cancer and/or heart disease, plus a laundry list of other ailments that result from the inhalation of bad stuff.

If you're just waiting for a bus next to someone smoking and you get the occasional whiff of their Marlboro, nothing quantifiable will result. But being a child in a house with indoor-smoking parents, or regularly visiting a smoky pub as an adult, raises your lung cancer risk. Working in a smoky pub raises it more.

The important detail to remember here, though, is that the incidence of lung cancer in non-smokers is low. Only about 15% of all lung cancers are found in non-smokers, and most of those seem, once again within the statistical limits of what epidemiology can tell us, to have been caused by something other than second-hand smoke.

Chronic exposure to highly polluted air, for instance, will do it. A traffic policeman in Beijing, Mexico City or Ahwaz, Iran really ought to wear a gas mask, or possibly SCUBA gear, to work.

Numerous other kinds of smoke are also carcinogenic. If you work in a commercial kitchen with woks full of smoking overheated oil all over the place, that's bad. So is wood smoke; it may smell nice, but it's definitely carcinogenic. Incense is bad for you, too.

And then there's radon, a well-known danger in the USA, but almost completely unknown here in Australia, where very few houses have basements. You'll probably only have much exposure to radon if you're a miner, of if you spend a lot of time in a basement or other poorly-ventilated underground room dug into high-radon ground.

Sundry inhaled particulate matter is also bad news. This is another problem for miners, and various other industrial workers.

And there are lung-cancer-causing viruses, too.

And then there's asbestos inhalation, of course. But that's much more likely to cause the horrible-but-not-cancerous disease asbestosis than it is to cause mesothelioma.

Or you could just be fortunate enough to be genetically predisposed to develop lung cancer.

If you're a non-smoker and you can avoid all of these risk factors, then the chance that you'll get lung cancer - or, at least, that you'll get it a long enough before some other disease kills you of "old age" for the lung cancer to become an actual problem - is very small. Second-hand smoke exposure that doubles your risk of cancer sounds scary, but if there's only a one in ten thousand chance that you'll get it in the first place, then the doubling only raises it to a chance of one in five thousand, which probably won't keep you awake at night.

And the risk from different causes isn't necessarily cumulative, either. If you're a non-smoker who works without breathing protection in the Acme Smoke, Flame and Asbestos Dust Factory in the Land Occupational Health and Safety Forgot, and as a result have a 50% chance of getting lung cancer in the next ten years, then heavy exposure to second-hand smoke while you drink your way to amnesia on the weekends may only raise your cancer probability to 51 per cent.

Or it may do more. Again, epidemiology. Pick a hundred coloured marbles from the barrel of a million, try to figure out what colour the rest of them are.

Some scientists have argued that there's a somewhat unexpected public-health benefit from indoor smoking bans. Not only do they keep second-hand smoke out of the lungs of non-smokers, but the nuisance of having to go and stand outside with the rest of the Tobacco Lepers causes smokers to smoke less, and become healthier. The evidence presented for this is generally a reduction of hospital visits for smoking-related heart and pulmonary disorders after indoor-smoking bans go into effect, but this is yet more epidemiology, so it's eminently possible that the effect is from an entirely different cause, or smaller than it seems, or even nonexistent.

(Workers who hate having to go out into miserable weather to get their fix could easily, for instance, use their ten-minute break to suck down as much smoke as they possibly can in that time, to "stock up" and make sure that they can make it to the end of the day without cravings. They could, thereby, get a lot more crap in their lungs than if they were still allowed to have a leisurely cigarette or two at their desk.)

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.