From Wikipedia, the free encyclopedia

Science desk
< December 30	<< Dec | December | Jan >>	January 1 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

Contents 1 December 31 1.1 Seeing the Moon in the morning 1.2 Ju 52 1.3 not logged in message? 1.4 Silence 1.5 Harry Potter and the Deadly Elbows 1.6 Birds hopping and walking 1.7 Antibiotics 1.8 NaF 1.9 Instant unconciousness from long-drop hanging?

[edit] December 31

[edit] Seeing the Moon in the morning

Right - I've looked through all the articles I thought were pertinent to my query, but couldn't find an answer, so I'm sorry if it's actually in there, but: is the moon present in the sky every night, whether it is visible or not? I'm inclined to believe this due to the sheer obviousness of it, and have rationalised it to myself by saying that the Earth completes one rotation in a day, whereas the moon takes almost a month to complete an orbit, so it will be present in the night sky since it is (almost) stationary as the Earth moves (until the Earth and Moon become mutually tidally locked?) The problem I'm having is the fact that sometimes the moon can be seen in the morning; surely on the opposite side of the Earth, where it is night, the moon should be visible, and yet cannot be, since it can't be in two places at once? Sorry for rambling, and thanks.

Yes, the moon is indeed in the sky every night, and every day. Just... not neccessarily in your sky.

Sky = everything above the ground and water

Your sky = everything you can see, standing on top of the nearest hill, mountain, or building.

Vranak 01:50, 31 December 2006 (UTC)

The Moon rises in the east and sets just in the west like the Sun, so it's in the sky about half the time, just as the Sun is -- but not at the same time. At full moon, the Sun and Moon are in opposite directions from the Earth, so one rises as the other sets, and the Moon is visible all night and not at all by day. About a week later, the Moon has advanced 1/4 of the way around its orbit. Now you see a half moon (called "third quarter") and it rises around midnight and sets around noon. Another week after that and the Sun and Moon are in more or less the same direction from the Earth: now it's a new moon and they rise and set at the same time, so now the Moon is in the sky all day, but invisible in the Sun's glare. (And if you can see it, it's a very thin crescent. You might be able to spot it just after sunrise or just before sunset, depending on which side of the Sun it's on.) Another week or so and it's "first quarter", with a half moon rising around noon and setting around midnight.

As for people on the other side of the world, they will see the Moon and Sun in the same relationship to each other as you do. So if the Moon rises at noon Eastern Daylight Time on a particular day in New York, it also rises at noon Pacific Daylight Time in San Francisco and noon British Summer Time in London -- more or less, that is. It doesn't have to be in the sky simultaneously in two different places, although if they aren't exactly opposite each other on the Earth, it certainly can be.

All of this description is a bit approximate, because the Moon's orbit is not circular and is not in the same plane as the Sun's (and for my last paragraph, the use of zone times add a further inexactitude). My intent was just to give a general picture. This web page at the U.S. Naval Observatory will compute exact times for the rising and setting of the moon as well as the sun, for any date you choose, for any city in the U.S., or for any place worldwide if you can supply the correct latitude, longitude, and time zone.

--Anonymous, December 31, still 2006, 02:22 (UTC).

The only way for the Moon to be "up" and yet not visible is if there is heavy cloud cover. The Moon typically shines through light clouds. (You might think a new moon wouldn't show up at night, but those only occur during the day, anyway.) StuRat 02:28, 31 December 2006 (UTC)

The images at Lunar phase may help to think about this.  --Lambiam^Talk 06:29, 31 December 2006 (UTC)

In short, the Moon is up on almost all nights, if we define night to be the time between the exact moments of sunset and sunrise. However, what if new moon occured during the night in your location? By sunrise, the Moon would already be on the other side of the Sun, and will therefore rise later than the Sun. So that's one night without a moon.

By the way, the Moon usually cannot be observed for a day before or after new moon. [1] It's very difficult to see a thin sliver of light against the much brighter twilight sky. --Bowlhover 09:29, 31 December 2006 (UTC)

Also by the way, the Moon is not the only celestial body that's easy to see at night but also visible in the daytime. This is also true of Venus. Since it orbits the Sun in a smaller orbit than the Earth's, we never see it in the direction away from the Sun, but always somewhat toward the Sun, as a crescent moon is.

For example, if on a particular date the Sun rises at 7 a.m. and sets at 5 p.m., then Venus might rise at 9 a.m. and set at 7 p.m. (in which case it is "the evening star") or rise at 5 a.m. and set at 3 p.m. (as "the morning star"). In these cases you would be able to see Venus in the daytime sky if you just know where to look. If you see it one day well above the horizon at dawn, as the morning star, and you have the time to do so, try keeping track of its position as the Sun rises ("okay, last time I looked it was that far above that building; ah, now it's moved a bit that way") and you'll see that it remains visible as the sky turns blue and stays visible through the day.

Of course, on another day Venus might be closer to the Sun and would be lost in its glare in the daytime. --Anonymous, December 31, still 2006, 09:57 (UTC).

However, it is possible, though maybe not easy (depending on the person), to see Venus in daylight. Vultur

[edit] Ju 52

In Junkers Ju 52:

The aircraft's unusual corrugated metal skin strengthened the fuselage and gave it a characteristic boxy appearance.

I can understand how corrugated metal skin strengthens the fuselage. How does it strengthens the wings? The corrugated metal of Ju 52 only strengthens the wings against chord-wise forces. It does not help against span-wise deform which can be much stronger.

Why did they corrugate duralumin? Was the duralumin available during the WW2 suitable for so much repeated cold working? -- Toytoy 01:25, 31 December 2006 (UTC)

The Ford Trimotor also has a very similar design:

its wings were made of aluminum and corrugated for added strength ... All models had aluminum corrugated sheet metal body and wings.

It looks so strange that they added strength in a direction that needed least strength ... -- Toytoy 05:23, 31 December 2006 (UTC)

I'm not familiar with the terminology, but what I presume you call span-wise deforms have little impact on the flight characteristics. In fact, substantial flexibility is desired in case of a sudden vertical draft. But the other (chord-wise?) deformations change the angle of attack and have a large impact. You don't want any flutter and possible resonance there, so stiffness is critically desired.  --Lambiam^Talk 07:15, 31 December 2006 (UTC)

[edit] not logged in message?

Why does it say that I'm not logged in when I try to edit a message even though I am logged in? —The preceding unsigned comment was added by 67.142.130.31 (talk) 02:52, 31 December 2006 (UTC).

What is the "it" that says so, what is the system you are logged in to, and what kind of messages are you attempting to edit?  --Lambiam^Talk 07:18, 31 December 2006 (UTC)

I think the poster is saying that when he tries to edit Wikipedia, the edit page shows the message "You are not currently logged in". In that case, do you see your username at the top after clicking "edit this page"? Are you really still logged in? --Bowlhover 08:45, 31 December 2006 (UTC)

If I had to guess, I'd say you might be having cookiee issues, try clearing your cache--71.247.246.54 16:28, 31 December 2006 (UTC)

Do Wookiees eat cookiees?  --Lambiam^Talk 19:22, 31 December 2006 (UTC)

No, but a lot of browsers do--71.247.246.54 15:02, 1 January 2006 (UTC)

[edit] Silence

Whenever it is silent, I hear a type of static, which might get louder the more silent the place I am in is. I noticed that I can bend the pitch of the static with my mind. What is this static called, and does anybody else get that? I can hear CRT televisions (as a high-pitched noise) when they are on, even if the speakers are muted, if that makes a difference. --Shanedidona 06:05, 31 December 2006 (UTC)

Young people usually can hear the high-pitched CRT television sound, at the frequency of the sweep oscillator. What you may be hearing when it is silent is the sound of blood circulating.  --Lambiam^Talk 06:42, 31 December 2006 (UTC)

No, it is real, I've heard that before, and I've made an experiment by myself by turning on and off the television with the remote. It only sounds when the TV is on, even at volume zero, and stops when the TV is turned off, so it can't be just blood flow. (I've done this hundreds of times, so I'm convinced of the results...) Titoxd^(?!?) 08:53, 31 December 2006 (UTC)

Lambiam was talking about two different effects. The CRT sound is the sweep oscillator, also called the "flyback". Its frequency is the frame rate times the number of lines on the screen, or around 15-16 kHz. Hearing your own blood is also possible, but not likely something whose pitch you can "bend with your mind". --Anonymous, December 31, still 2006, 10:02 (UTC).

I was talking about 2 different effects (silence and TV). I was ambiguous in my wording. --Shanedidona 15:28, 31 December 2006 (UTC)

You might see if Tinnitus describes what you are experiencing during silence. Geologyguy 15:47, 31 December 2006 (UTC)

My friend once described how, during a state of heightened hearing, bothered by the ambient noise, he went around the house and unplugged every electrical device he could find. It got a little bit quieter each time, but he was never able to totally eliminate the sound. We surround ourselves with so many electromagnetic fields, perhaps you're picking something up in that way? I wonder if you would hear it somewhere like a subterranean cave, far removed from all the (literal) hum of society? -GTBacchus^(talk) 21:53, 31 December 2006 (UTC)

Won't add more about the flyback oscillator, except to say that the crystals used there have, due to their cheapness, found their way into more expensive products, such as ultrasonic body scanners.

As to bodily generated sounds: 1. My tinnitus (mild) is modulated by my heartbeat. Quite audible in a quiet room. 2. Tension in my jaw muscles (whether normal tonus or patholigical is unknown) causes a humming which can be disconcerting when first discovered. Altering the position of the head (when lying down) will alter the pitch; and to some degree the strength of the sound.

As to heightened sound sensitivity, I experienced that due to spontaneous medititative states as a teenager. Only physical movement (walking) or dispersal of attention (distractions) would release me from this unspleasant phenomenom.

In summary, try moving the jaw, trying to relax the muscles.

Tinnitus, as mentioned by Geologyguy, is almost certainly what is being asked about; for many, it's perceived as white noise while, for those less-fortunate, it's perceived as discrete tones (the "ringing in the ears" that you hear mentioned). The bad news: It eventually happens to most everyone and it will probably get worse as you get older.

But the modern world is also a very noisy place. Our houses do, indeed, have a huge number of background noises including electrical humming, refrigerators vibrating, furnaces whirring, pilot lights whispering, and the like. And even if your house is quiet, you can often still hear the road or motorway several miles away. Or the rifle range. Or the airport. If you're looking to hear birds twittering in otherwise-silence, you'll need to go a surprising distance from the nearest (alleged) "civili[s/z]ation". And even then, peepers and cicadas may have other plans for you.

Atlant 14:19, 2 January 2006 (UTC)

I remember reading somewhere that this buzzing sound has religious significance. You may want to look into hinduism and/or vedic philosophy.--Joel 01:42, 5 January 2006 (UTC)

[edit] Harry Potter and the Deadly Elbows

when is Harry Potter and the Deadly Elbows coming out? Rugbyball 11:32, 31 December 2006 (UTC)

-Pretty sure it never will be, don't think it's a title and to be honest I think you knew that or at least should have known that. Also is that related to Science in any way? Howso-Mchowsoson 11:45, 31 December 2006 (UTC)

Assuming OP means Harry Potter and the Deathly Hallows, our article says publication date is uncomfirmed but is "likely" to be sometime in 2006. However, you can pre-order the book on Amazon (and probably from other booksellers as well). Gandalf61 13:45, 31 December 2006 (UTC)

It's currently the Amazon best-seller. I think it will be safe to speculate that it will contain no science whatever.--Shantavira 16:04, 31 December 2006 (UTC)

[edit] Birds hopping and walking

Can anyone explain to me why some birds hop and some birds walk? Rthorner 14:43, 31 December 2006 (UTC)Rosie

I would think that smaller birds would need to hop to get over grass, etc., which would impede walking. Hopping does take more energy, though, so large birds, which don't need to hop, don't. StuRat 15:49, 31 December 2006 (UTC)

"Differences in gait depend basically on differences in environment. For a bird which spends much of its time in trees or bushes, the best way to move from branch to branch is by hopping. But hopping is an inefficient, energy-consuming way of getting about on flat ground. Species such as larks, pipits and starlings, which spend a good deal of time on the ground, have therefore evolved a way of moving on land which is more economical – walking." (Courtesy of my Book of British Birds).--Shantavira 16:15, 31 December 2006 (UTC)

Where do corvids (or at least European magpies) fit into this? They do both. --Kurt Shaped Box 19:42, 31 December 2006 (UTC)

Body structure, skeletal form, musculature. I've noted that while gulls generally walk, crows will both hop and walk. Vranak 23:37, 31 December 2006 (UTC)

Ever see a gull walking along a long, thin perch (such as an iron railing or the apex of a roof)? They're clearly not 'designed' to walk by putting one foot in front of the other and as they don't seem to be able to shuffle sideways (gulls don't do trees and have inflexible feet), they wobble precariously with their back end swinging back and forth as they try to maintain balance. Picture an obese human trying to walk along a tightrope. It's quite amusing to watch - they slip and fall quite often. On the other hand, on flat ground a gull can outrun a sprinting human. --Kurt Shaped Box 03:50, 1 January 2006 (UTC)

They say some birds hop to trick worms into thinking it is raining.Hidden secret 7 21:33, 5 January 2006 (UTC)

[edit] Antibiotics

How long do strong antibiotics stay in the system, after finishing a coursePetelangley 15:42, 31 December 2006 (UTC)

• Really depends very strongly on what class of antibiotics you're talking about, on the whole, an antibiotic isn't much more than a broad term for something with antibacterial activity. Thus, impossible to answer your question without knowing what specific antibiotic--71.247.246.54 16:23, 31 December 2006 (UTC)

For various reasons, antibiotics are frequently not used in pharmacokinetically "ideal" ways (which is what a doctor would do if he simply wanted to achieve an effective steady state in the blood stream.) Never the less, as a rough guide, the elimination of a drug can be taken at approximately 5 times the normal dosing interval. So if you take a drug once a day, it should be virtually absent after 5 days. Normally taken every 12 hours, it should be absent by 2½ days. Taken every 8 hours, one can guess that it should be eliminated in less than two days--Seejyb 23:34, 31 December 2006 (UTC)

[edit] NaF

chemical reaction in manufacturing sodium fluoride (NaF) from Sodium fluorosilicate/Sodium silicofluoride (Na₂SiF₆)—The preceding unsigned comment was added by Sarangrdeshpande (talk • contribs).

That is a statement, not a question. Rugbyball 17:03, 31 December 2006 (UTC)

I assume they're asking "What is the chemical reaction that ..."--71.247.246.54 12:58, 1 January 2006 (UTC)

[edit] Instant unconciousness from long-drop hanging?

An unpleasent subject, but Saddam Hussein was recently executed by long drop hanging. It is claimed this causes instant unconciousness and/or instant death by breaking the spine and presumebly the spinal chord. What is the mechanism that connects a broken neck with instant unconciousness? Is this in fact true?

I can understand how beheading or guillotening results in unconciousness because the drop in blood pressure causes fainting, the mechanism of which evolved to make the body fall to the horizontal and have the heart at the same level as the brain. But what about a broken spinal chord? —The preceding unsigned comment was added by 80.0.134.52 (talk) 18:59, 31 December 2006 (UTC).

It causes paralysis. --Proficient 19:35, 31 December 2006 (UTC)

Right, but paralysis doesn't cause instant unconsciousness. --Wooty Woot? contribs 22:15, 31 December 2006 (UTC)

From the article hanging, it appears that the goal is to be as close as possible to beheading, without an actual separation. I would guess the blood pressure shock to the brain would be sufficient for an instant effect. --Zeizmic 22:57, 31 December 2006 (UTC)

Instant unconsciousness is a fantasy maintained by those who think that capital punishment is a good and moral thing for their state to do on their behalf.

Atlant 14:32, 2 January 2006 (UTC)

This article on hanging from the "Capital Punishment U.K." site has a description. The instant loss of consciousness is due to: "... massive blow to the back and one side of the neck, which combined with the downward momentum of the body, breaks the neck and ruptures the spinal cord causing instant deep unconsciousness and rapid death. Due to its position under the angle of the left jaw, the head is snapped backward with such force that the posterior aspect of the foramen magnum cuts the spinal cord superior to the top vertebra and just a little inferior to the brain stem." The C2,3 and 4 fractures are called "hangman's fractures", but there are descriptions of persons walking around with these for a few days (after motor vehicle accident) before diagnosis of the sore neck! It is the force of the blow that makes the difference. --Seejyb 23:20, 31 December 2006 (UTC)

Force, as they've said. Imagine instead of this being done by body weight, you hit someone on the back of the neck (or you hit someone in the right place on their jaw) with sufficient force to cause unconsciousness and to break the neck. On the subject of losing consciousness or not following non-traumatic spinal cord severing, I believe experiments have been done with animals that demonstrate that consciousness is retained, and quadraplegics with high spinal cord damage demonstrate that severing the spinal cord doesn't cause death. Regarding beheading, I recall some tales from the French Revolution, particularly during The Terror, of heads in baskets after guillotining still moving their eyes for a few seconds after beheading. The tales of heads speaking are probably apocryphal. Carcharoth 02:15, 1 January 2006 (UTC)

Ah. Here we are: Guillotine#Living_heads:

The following report was written by a Dr. Beaurieux, who experimented with the head of a condemned prisoner by the name of Henri Languille, on June 28, 1905:[2]

"Here, then, is what I was able to note immediately after the decapitation: the eyelids and lips of the guillotined man worked in irregularly rhythmic contractions for about five or six seconds. This phenomenon has been remarked by all those finding themselves in the same conditions as myself for observing what happens after the severing of the neck...

"I waited for several seconds. The spasmodic movements ceased. [...] It was then that I called in a strong, sharp voice: 'Languille!' I saw the eyelids slowly lift up, without any spasmodic contractions – I insist advisedly on this peculiarity – but with an even movement, quite distinct and normal, such as happens in everyday life, with people awakened or torn from their thoughts.

"Next Languille's eyes very definitely fixed themselves on mine and the pupils focused themselves. I was not, then, dealing with the sort of vague dull look without any expression, that can be observed any day in dying people to whom one speaks: I was dealing with undeniably living eyes which were looking at me. After several seconds, the eyelids closed again, slowly and evenly, and the head took on the same appearance as it had had before I called out.

"It was at that point that I called out again and, once more, without any spasm, slowly, the eyelids lifted and undeniably living eyes fixed themselves on mine with perhaps even more penetration than the first time. Then there was a further closing of the eyelids, but now less complete. I attempted the effect of a third call; there was no further movement – and the eyes took on the glazed look which they have in the dead.''

Yeah, I know, it's not hanging, but I couldn't resist it. Carcharoth 02:20, 1 January 2006 (UTC)

I suppose the purpose of the very big knot on the noose must have been to deliver the knock-out-blow referred to above. I am surprised they were generous enough to give him a quick death from a long-drop rather than making him dangle suffocating from a shorter drop.