Science desk
< May 25	<< Apr \| May \| Jun >>	May 27 >

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.

May 26[edit]

dangling inchworms[edit]

I live in/around Boston, Massachusetts---In this time of year, I see these little inchworms dangling off trees on their very fine threads. From some casual googling, it is my understanding that they're trying to reach the ground. If this is the case? What the heck takes them so long? They seemingly just dangle and dangle, never actively pursuing the ground at all!

Care to shed any light on what they heck these little guys are up to?

(I know not the sciencey name for my little friends, but they are small and green)199.94.68.201 (talk) 00:58, 26 May 2011 (UTC)[reply]

See Ballooning (spider). Wnt (talk) 02:10, 26 May 2011 (UTC)[reply]

The inchworms (caterpillars for UK readers) may not necessarily be trying to reach the ground. It is possible that they are trying to avoid predators that have encountered them on a leaf. This is a strategy pursued by a number of microlepidoptera and sawflies, See here. Richard Avery (talk) 07:18, 26 May 2011 (UTC)[reply]

Some also form a cocoon on the end of a thread, but it's usually a short one. StuRat (talk) 04:18, 27 May 2011 (UTC)[reply]

Why can't (don't?) we mass produce space probes?[edit]

The Spirit and Opportunity rovers have lasted many times their expected lifetimes. Since they are already designed and proven to function, wouldn't it be worthwhile to modularize their construction and send many more to Mars? How much of the cost of a project such as the Mars rovers is in development vs actually getting them to their destination? 68.231.149.156 (talk) 02:27, 26 May 2011 (UTC)[reply]

NASA Mission Profile says the total cost of the Spirit and Opportunity missions was "approximately $820 million total, consisting approximately of $645 million spacecraft development and science instruments; $100 million launch; $75 million mission operations and science processing". Gandalf61 (talk) 11:41, 26 May 2011 (UTC)[reply]

So they should be amenable to the economics of scale, right? Also, if you can scale the production up why not send these little suckers to every massive body we can reach? 169.234.143.14 (talk) 14:11, 26 May 2011 (UTC)[reply]

They were designed to work on Mars, not elsewhere. Mercury and Venus would be too hot for them. The outer solar system wouldn't have enough sunlight to power them. They might work on the asteroids, I suppose, but really they only work properly on Mars. There isn't much point sending more of them to Mars - you would rapidly get diminishing returns. We've already learned most of what they are capable of teaching us about Mars. --Tango (talk) 19:30, 26 May 2011 (UTC)[reply]

We can easily mass-produce space-probes. We just can't put them in space for cheap! It is the launch-vehicles (rockets, or space shuttles, or space elevators) that are prohibitively expensive. One of the major objectives of the long-term NASA program, Space Shuttle, ("Space Transportation System") was to launch thousands of space-borne experiments, re-using the launch vehicle. (The humans were just along for the ride). Each mission carried dozens or hundreds of individual experiment packages.

More recently, NASA has been pitching CubeSats; again, the idea is that if we are sending one rocket up, we might as well pack it with as many space-borne experiments as possible.

I recently saw a semi-tongue-in-cheek presentation at NASA Ames wherein an off-the-shelf Android device was being touted as a cube-sat computer and sensor-package. (I suspect some engineering issues will arise, but the concept is actually not such a bad idea). A fully-functional computer and sensor package can cost a few hundred dollars; but a low-earth orbit launch will still cost tens of millions of dollars. Nimur (talk) 16:40, 26 May 2011 (UTC)[reply]

Black hole-like phenomena from other forces?[edit]

Hello, I have read that spacetime is severely distorted by the strong gravity of a black hole. Is it possible thatother forces, perhaps the strong force or electrostatic force, could distort space to a comparable extent, although maybe not into the same shape(eg., not as centrosymmetric)? Thanks.--Rich Peterson24.7.28.186 (talk) 03:07, 26 May 2011 (UTC)[reply]

Sonic black holes may be of interest 213.49.109.8 (talk) 05:35, 26 May 2011 (UTC)[reply]

Or Black hole electron. Graeme Bartlett (talk) 11:46, 26 May 2011 (UTC)[reply]

Isn't the short answer as to why no analogous structure has been predicted or observed, is that the analogy between gravity and electric forces is only so good. There are only attractive forces in gravity, while there are attractive and repulsive forces associated with electricity. 169.234.143.14 (talk) 14:14, 26 May 2011 (UTC)[reply]

Other forces don't distort space-time, other than by contributing the the stress-tensor, see e.g. Reissner–Nordström metric. Count Iblis (talk) 14:37, 26 May 2011 (UTC)[reply]

Thanks, all of you.-Rich24.7.28.186 (talk) 04:25, 30 May 2011 (UTC)[reply]

Star colors in M13[edit]

In Messier 13, almost all of the stars seem blue, with a few prominent yellow stars: http://en.wikipedia.org/wiki/File:Heart_of_M13_Hercules_Globular_Cluster.jpg

Why is this the case? I thought that since a globular cluster's stars are very old, they should almost all be yellowish. --140.180.16.144 (talk) 10:52, 26 May 2011 (UTC)[reply]

I think the impression that "almost all of the stars seem blue" is illusory - the blue ones seem prominent because they are generally brighter, while the large majority of the cluster's stars are yellow or white, but dimmer. Nevertheless there are clearly more than a few blue stars and, as you imply, one would think that if they were as old as their cooler cluster-mates, they should have gone by now.

My understanding is that the blue stars are likely younger than the cluster as a whole, but that the reasons for their anomolous presence are not yet generally agreed on. Relevant articles/sections that may shed some light (sorry!) are Globular_cluster#Color-magnitude_diagram and Blue straggler. {The poster formerly known as 87.81.230.195} 90.201.110.74 (talk) 11:41, 26 May 2011 (UTC)[reply]

I will mention that the picture is a false-color (or at least pseudocolor) image. The (Hubble Space Telescope) camera used for the image is a monochrome CCD; 'color' images are produced by combining exposures collected with different colored filters in front of the image sensor. If you click on the image, you'll find a description page (and further links) describing how this particular picture was generated. Briefly, the blue, green, and red channels in the picture as displayed actually represent the light seen by the camera through blue, red, and infrared filters. The different color channels were exposed for different lengths of time, as well—but that may be due to different intrinsic light transmission properties of the filters. (The 'blue' filter may pass a narrower range of wavelengths than the 'red' filter, and so need a correspondingly longer exposure time; you'll have to investigate.) Features that appear 'white' in this image probably map to yellow or red in real life. TenOfAllTrades(talk) 15:39, 26 May 2011 (UTC)[reply]

Senior Analyst - qu'est-ce que c'est?[edit]

I recently came across an ad for a "Senior Analyst" position at a research institute. What does the "Senior Analyst" really mean in this context? I've spent over 20 years in science but I never heard of such a position in a scientific institution. Thanks in advance. --Dr Dima (talk) 18:27, 26 May 2011 (UTC)[reply]

"Analyst" is a catch-all job title for a very wide range of actual roles in a wide range of different organisations. It's common for pretty much everyone in a department (or at least all the junior staff) to be an "analyst". A "senior analyst" is just an analyst that has been around for a few years. --Tango (talk) 19:35, 26 May 2011 (UTC)[reply]

La question est simple, c'est l'Analyste Aîné. Cuddlyable3 (talk) 12:11, 28 May 2011 (UTC)[reply]

Riding out storms in bathtubs[edit]

It's often said that one place to ride out tornados is in the bathtub due to the protection that it offers. I wouldn't want to lie face down because that exposes the spine to falling debris. This also lowers your airway, so if you're pinned and the tub fills with rain water, you could drown. Face up exposes your full gut and chest, which again could be bad. So that leads me to believe that laying on your side with arm along your exposed side is the best route. So, if you lie on your side, which is the best, if there is such a thing, to have up or down? I'm thinking having the side with more lone organs (pancreas, gall bladder, etc but not including kidneys since you have two) facing down would be best but maybe there's something I haven't taken into account. Dismas|^(talk) 18:46, 26 May 2011 (UTC)[reply]

Is it really often said that you should get in the bathtub? I would get underneath something strong and heavy, like a big table or bed, so that things couldn't fall on me. --Tango (talk) 19:57, 26 May 2011 (UTC)[reply]

I'm not the only one who has heard of it. Dismas|^(talk) 20:38, 26 May 2011 (UTC)[reply]

I've heard of that, and it's better than nothing, but getting under a heavy table, or under something heavy and sturdy, is a better bet, especially if it's in the basement. The basement is the best place to be in general, because no matter where you hide, if your house takes a direct hit from a tornado, you're basically screwed... or at least the house is. The house is not necessarily all that likely to collapse, it's more likely to be smacked off its foundation. Think of a tornado as being like a large fist. So the basement is the safest place, in general. Barring that, an interior room away from glass. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:17, 26 May 2011 (UTC)[reply]

I'd have to disagree; The most important thing with tornadoes is lateral protection: when a portion of a house collapses, it almost never collapses straight down; and once it does, the tornado is blowing things around horizontally at deadly speeds. Also, if you are in the tub you do have protection on top, since it's likely that heavy debris will just lay across the top, while anything that would actually fit into the bathtub with you wouldn't be heavy enough to kill you. I have heard many stories of people surviving F5/EF5 tornadoes in a bathtub (the 1997 Jarrell tornado and the recent 2011 Joplin tornado just to name two). Sure, the basement is by far the best place, and getting under a heavy piece of furniture in the basement is just an added bonus of protection, but without a basement (as with the majority of people in Tornado Alley) I would say the bathtub is the best place to be, with a mattress and/or blankets on top for extra protection.-RunningOnBrains^(talk) 10:33, 27 May 2011 (UTC)[reply]

A bathtub is good because it's in a bathroom, and a bathroom is good because it's typically a small room (and thus, stronger) towards the core of the building (thus, less likely to collapse even if the rest of the building does) with small or no windows (thus, no flying glass). The tub itself provides a little bit more protection, in that if the bathroom walls do collapse, they'll only harm you if they do so with enough force to crush the tub. --Carnildo (talk) 22:25, 26 May 2011 (UTC)[reply]

It's better than nothing, but bathrooms typically have mirrors, which are typically made from glass. The dilemma regarding tornadoes is that there may be very little warning and you may have only seconds to take cover. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:36, 26 May 2011 (UTC)[reply]

No room is really going to be free of sharp objects that can cut you; a mirror does not present nearly the hazard that windows do because they have one side on a wall, so they're not going to spread glass violently.-RunningOnBrains^(talk) 10:33, 27 May 2011 (UTC)[reply]

The great majority of tornadoes are not strong enough to blow down a typical house -- they blow out windows and tear off roofs and send debris flying around, but the walls remain intact. For those sorts of things, a bathtub is pretty decent protection. The sort of tornado that struck Joplin is a whole different story. Looie496 (talk) 23:11, 26 May 2011 (UTC)[reply]

A direct hit from even a mere EF1 can do lots of damage. You're right that the EF4's and 5's are a lot rarer and a lot more damaging. Those are the kinds of storms that turn up in tornado alley (Kansas and Oklahoma) and neighboring states. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:44, 26 May 2011 (UTC)[reply]

He's right in that most tornadoes will only cause superficial/external damage, which leaves the integrity of the structure intact. An EF1 or EF2 usually won't level a well-built house. That said, tornadoes fluctuate in intensity very rapidly, and an EF0 may mature into an EF3 in a few minutes. If I know for a fact I'm in the path of a confirmed tornado, I'm not going to wait to see how strong it is when it gets to my front door. A basement is obviously the best place to seek shelter, followed by an interior closet, and if all else fails, the bathtub with a mattress over you to shield you from falling debris. As noted above, the EF4s and EF5s that hit Tuscaloosa, Joplin, El Reno, etc not only level but completely wipe out all structures, so if you don't have a basement, your only hope is for an anomalous corner of safety under somewhat stable debris. Frankly, I would never climb under a bed or a desk or something... tornado damage is very fickle, and you have no way of knowing which way the bed or table will be blown, covered, or broken. The last thing I want is to be trapped. Juliancolton (talk) 23:50, 26 May 2011 (UTC)[reply]

It's of note that in places where tornados are common, it is usually the poor who don't have basements or better shelters. The tub is really not ideal, but in a series of non-ideal options, being in a tub is probably the most structurally secure place in a home, assuming it doesn't have a basement. I've also heard people recommend trying to put a mattress over yourself while in the tub. That's desperation as much as anything else. --Mr.98 (talk) 00:46, 27 May 2011 (UTC)[reply]

See my above suggestions re. the mattress. ;) Having studied meteorology for 12 years now, that's definitely something I would encourage. A very small piece of airborne wood or metal can injure you severely, and the mattress protects from a lot of that small flying debris. It won't keep a wall up, but if it's just glass and things flying around, it's a huge positive factor. Juliancolton (talk) 01:04, 27 May 2011 (UTC)[reply]

The "mattress on top" was the missing piece where the bathtub scenario is concerned. As a practical matter, it might not be so easy to find a mattress in the few seconds before a tornado hits. But if there are tornado warnings in the area, there could be time to make preparations. The important thing is to plan ahead. Unlike hurricanes, which move slowly enough to be avoided, tornadoes can spring up very quickly. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:07, 27 May 2011 (UTC)[reply]

The average warning time is 14 minutes, which should be enough to yank the sheets off and get the mattress over you. But obviously, some tornadoes occur in HP supercells and are obscured by rain, some occur at night, and some simply touch down a mile or two away and hit you before you know what's coming. There's simply no one answer for how to stay safe. Juliancolton (talk) 01:23, 27 May 2011 (UTC)[reply]

Perhaps a specially designed suit containing body armor on the outside and shock absorbers on the inside could work. The inside would then look like this:

Count Iblis (talk) 01:10, 27 May 2011 (UTC)[reply]

Sigh. You know someone at Commons is probably going to end up deleting that as a copyright violation. Three-dimensional sculptures and freedom of panorama and all that. Wnt (talk) 17:32, 28 May 2011 (UTC)[reply]

So, nobody has an answer to my question then? Dismas|^(talk) 03:03, 27 May 2011 (UTC)[reply]

Get in your bathtub, under something protective like a mattress, and into a comfortable and protected position. Don't worry about the tub filling with rainwater. That's very unlikely. Your much greater danger is from flying debris. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:17, 27 May 2011 (UTC)[reply]

Agreed. Plus, don't bathtubs have like, a hole on the bottom? :)

In all seriousness though, you're really splitting hairs at the point you're talking about what position would let you survive the most. If you're crushed by debris it's not really a directional injury; it's going to hurt you through and through, and getting hit by high-velocity debris that would cause a piercing or blunt-force injury is unlikely in the bathtub because the really fast debris is traveling horizontally. Really the most important thing to protect is your head; I've heard advice (that I 100% agree with) to grab a bicycle helmet and put it on if you have one.-RunningOnBrains^(talk) 10:33, 27 May 2011 (UTC)[reply]

Thank you! I appreciate the responses. Dismas|^(talk) 01:06, 29 May 2011 (UTC)[reply]