Wikipedia:Reference desk/Archives/Science/2013 April 23

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Science desk
< April 22 << Mar | April | May >> April 24 >
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.

April 23[edit]

A Jupiter-sized planets survive being swallowed up by parent star[edit]

From [1] shows two planets got swallowed up by their parent star and end up survived through white dwarf. Then how earth-liked small planets just get engulfed eventually 200-1000 years in sun's layer but if Jupiter-sized planet got swallowed by host star can actually survive. If a Jupiter-sized planet have initial distance from sun to Mercury or 0.2 AU tot he sun and they got swallowed up by giant star is this possible they can still survive through white dwarf. How can gas giant planets atmosphere survive at that high temperature of over 2000 K? Can gas giant planets ocean and atmosphere actually penetrate through inside sun's atmosphere layer? Or is because of the Jupiter sized planets have relatively low density, they sink in sun's layer slower than rocky earth-liked planets. If a brown dwarf or red dwarf star got swallowed up by red giant can they also survive but not destroyed eventually?-- (talk) 00:01, 23 April 2013 (UTC)

Jupiter is almost large enough to become a star itself. If it was sufficiently heated, I wonder if fusion would start inside it, at least until the red dwarf contracted away from it. In any case, the much greater density of Jupiter than the thin outer layers of a red giant would mean it would be more likely to steal material from the star than vice-versa. StuRat (talk) 01:58, 23 April 2013 (UTC)
According to the article on stars, Jupiter is 87 times too small to be a star. And "heating" does not figure into it, stars fuse atomic nuclei because of quantum effects caused by high pressure in the stellar core; see stellar nucleosynthesis. (talk) 10:35, 23 April 2013 (UTC)
In addition to being 87 times too small, Jupiter is 13 times too small for deuterium fusion (see brown dwarf). It is also not true that "it would be more likely to steal material from the star than vice-versa" because the article says the exact opposite. -- (talk) 14:03, 23 April 2013 (UTC)
If you refer to the article the OP linked to, I wouldn't put too much faith in anything written by someone who can't tell 5 million from 5 billion. StuRat (talk) 00:14, 24 April 2013 (UTC)
The article referenced by says "It's about five million years until we can expect the same fate on Earth. But, eventually, our sun will swell up to become a red giant, an inflated star that has used up most of its fuel. It will grow large enough to swallow Mercury, Venus, Earth and Mars." Isn't that an unrealistically short timeframe for the Sun to become a red giant and engulf the Earth? Is it a case of "tomayto, tomahto, million, billion, what's the dif to the scientifically illiterate and/or careless science writer?" Edison (talk) 02:37, 23 April 2013 (UTC)
Another source like [2].-- (talk) 03:54, 23 April 2013 (UTC)
Yes, and that one correctly says billion. If the woman who wrote the first article claims she used her "wits" to get the job, we might well expect a typo, there, too. StuRat (talk) 04:30, 23 April 2013 (UTC)
Pwned. - ¡Ouch! (hurt me / more pain) 13:45, 23 April 2013 (UTC)
"Excuse me, Doctor, did you say that the Sun will burn up the Earth in 5 billion years?"
"Yes, more or less."
"Thank God. For a moment I thought you said 5 million." BILLIONS AND BILLIONS, Carl Sagan
The classics, they never die. Gzuckier (talk) 17:06, 23 April 2013 (UTC)
Moreover, the sun is not a white dwarf, and it won't swallow Mars. Plasmic Physics (talk) 04:33, 23 April 2013 (UTC)
I've swallowed a Mars before, but I prefer Snickers. --Jayron32 05:04, 23 April 2013 (UTC)
Ha, you made a funny. Plasmic Physics (talk) 07:26, 23 April 2013 (UTC)
This is what the second site I linked said Scientists believe all the planets from Earth inward will be destroyed when the sun expands, but new research suggests that if planets are large enough, they may outlast their parent star's death, even if they are engulfed..

I think the first site that women meant sun's giant expansion might hit Mars orbit, but Mars will have escaped destruction by that time, if the sun gets that big. So Mars will not be swallowed up. Recent people, I know make careless mistakes, everybody does it recent days just anywhere.-- (talk) 05:09, 23 April 2013 (UTC)

To understand how atmosphere survives, look up scale height, atmospheric escape, escape velocity. It has to do with the level of gravity, the rate at which gravity decreases going away from the planet (big planets stack log factor after log factor of decrease of density in their atmospheres as you go up), versus the temperature and mass of the molecules seeking to escape. Wnt (talk) 22:06, 23 April 2013 (UTC)

Electronic welding helmets[edit]

hi could u please explain the tech behind the electronic screen .how could i make my own screen thanks — Preceding unsigned comment added by Mouthorgan (talkcontribs) 23:00, 23 April 2013 (UTC)

I suspect you are talking about Speedglas, it's a patented technology, so I don't like your chances of making one at home from scrounged components. The "main" part of it is a switchable LCD panel which darkens to a level similar to a normal welding visor's filter. Vespine (talk) 23:41, 23 April 2013 (UTC)
If the glass is only darkened when it receives an electrical impulse, I sure wouldn't trust it. One broken wire and the glass becomes clear while you are welding, then you are blinded. StuRat (talk) 00:10, 24 April 2013 (UTC)
Not surprisingly, the designers seem to have talkthought of this. The fail state is evidently an intermediate state (I had thought it may be darkest but that would potentially create additional problems and the fail state is suitable for welding in some cases) [3] [4] [5]. Of course it may still theoretically be possible for the device to show the lightest state when an arc occurs, but it'll likely take more then a single wire break, probably a very unlikely set of conditions. Anyway from what I can tell, even this sort of failure should not cause any sort of permanent damage, it's designed to protect against UV and IR rays whatever the state so I presume may dazzle or cause temporary blindess but probably not permanent damage (this obviously isn't a professional opinion, if you are actually welding I would hope you know more about this then me or at least know who to consult). They do give strong warnings about inspecting the device and also not continuing to use the device if it's not working. But the former would always be necessary since if the screen is physically broken it could result in permanent damage the same as with a normal safety shield. And as for the later, it's possible a single instance is fine but many instances over a short period of time are not and either way, if the devices are not working properly you do need to work out what's wrong, it could for example be a sign there is physical damage (and we get back to the former point).Nil Einne (talk) 00:44, 24 April 2013 (UTC)
Note that, before such things became available about 10 years ago, as an arc welder you sometimes had to look what you are doing to strike the arc, then QUICKLY move your face shield into place. With conventional arc welding faceshields, you cannot see a thing thru them unless the arc is burning. In other words, you have about a 10th or a 5th of a second to stop the arc and avoid eye damage even if the LCD type fails. It's no different to the occaisonal accidental glance straight into the sun. Wickwack (talk) 01:55, 24 April 2013 (UTC)
Again not medical advice, but as someone who has done a little bit of production welding, I suspect almost everyone who has done more then a little welding has accidentally expose their eyes to arc flash for very brief periods of time without any obviuous terrible consequences. It's certainly not something that will instantly blind you. Vespine (talk) 04:18, 24 April 2013 (UTC)
The ideal solution would be if your view was entirely blocked by a display screen, which would display what it sees on the attached cameras, with suitable processing to allow you to see both the arc and surroundings comfortably. The limitation, as I understand it, is that digital cameras are just as susceptible to damage from wildly varying light levels as our eyes are. Perhaps some system like what we use to view the Sun would work. The more sensitive camera would be positioned so that the arc is always blocked, and it would provide the background view. The less sensitive camera would look directly at the arc, with suitable filtering, and provide that portion of the picture. StuRat (talk) 05:07, 24 April 2013 (UTC)
I use cheap digital cameras ($20 webcams) inside my laser cutter - where your eyes would be irreversably damaged within a fraction of a second from IR, UV and very bright visual spectrum light. Both cameras have been staring unblinkingly at the business end of the machine 14 hours a day for close to 6 months now. That suggests that they'd do just fine in the scenario you envisage. SteveBaker (talk) 13:37, 24 April 2013 (UTC)
MannGlas is described in the article I linked, it's a welding helmet that uses high dynamic range imaging, digitally combining multiple images of varying exposure. It was invented in the 70s so probably far too expensive to be commerically viable back then. But with google glass around the corner, and displays and cameras cheaper then ever, if the concept was seriously revisitied now perhaps it would be a different story. Vespine (talk) 06:57, 24 April 2013 (UTC)
There is development on a newer version of this - but I don't recall where I read it. The videos were very impressive - due to the HDR imaging, the arc didn't saturate the image. The welder could clearly see the arc, along with the workpiece, their weld and all the background detail. I'm not a welder, but the welders I saw comment on it were amazed at how much better the image was than a traidtional view through a face shield. (talk) 12:03, 24 April 2013 (UTC)
Being, among other things, an occaisonal backyard/hobbyist welder myself, I can say that you soon get used to the traditional welding mask and you can see quite adequately to weld with the light from the arc a seen thru the traditional mask. Any complex camera system combining images therefore would have to be very cheap as the advantage to a skilled welder would be minimal. And it would necessarily need to be high definition. Wickwack (talk) 13:12, 24 April 2013 (UTC)
Digital cameras with 1080p resolution are down to $15 or so now...much less in bulk. Having several of them with different filters and some software to do the high dynamic range combining of their images would be something you could probably make for a few hundred dollars. The problem would be having a decent screen - preferably one that would preserve your 3D vision. The Oculus Rift head-mount display could do that really nicely...but that's several hundred bucks. I guess you'd need to sell these for around a thousand dollars. SteveBaker (talk) 13:37, 24 April 2013 (UTC)
I bet the price will rapidly fall at some point. Hopefully we won't have to wait for the patents to expire for the price to become reasonable. StuRat (talk) 18:02, 24 April 2013 (UTC)
I think ...107 above is talking about this: [6]. Link contains several videos, related links, and discussion. SemanticMantis (talk) 13:38, 24 April 2013 (UTC)