Science desk
< May 17	<< Apr \| May \| Jun >>	May 19 >

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 18

sun become a red giant 5 or 7.5 billion years?

Wait, I am a little confused here. said sun enter red giant about 5 billion years from now. Dr. Schroeder and Smith's website said tip of RGB is 7.59 billion years from now. Does it take 2.69 billion years for the sun to become a red giant, or sun last of red giant for 2.69 billion years. So when sun leaves main sequence in 5 billion years, it becomes a yellow subgiant first, and it slowly work the way to red giant by gradual increase of size/luminosity, or once it branches off main sequence it goes directly to red giant by large increase of size/luminosity. Is the end of red giant alot larger in diameter and luminosity then the beginning of red giant?--69.233.254.22 (talk) 01:32, 18 May 2012 (UTC)[reply]

According to Formation_and_evolution_of_the_Solar_System#The_Sun_and_planetary_environments, the process that leads to the formation of a Red Giant starts at around 5.4 billion years, and the process of growing into that phase will last until 7.5 billion years, so yes, it seems to take roughly about 2-3 billion years from starting on the red giant path and becoming a full-fledged red giant. --Jayron32 01:39, 18 May 2012 (UTC)[reply]

(edit conflict)Unfortunately I can't find the original website (I'd appreciate if someone could link to it) but 7.59 billion years seems like way too much precision to tell when the Earth will be consumed by the sun, especially since it is up for debate whether that will even happen.

The timeline you have sketched is about right though. See the text and charts at Sun#Life_cycle. The sun will start fusing helium at its core in around 5 billion years, which would technically be the start of its red giant phase. From there its luminosity and size will continue to increase over the course of 2-3 billion years, while the surface temperature will decrease. At some point in this expansion phase the earth may be destroyed, likely towards the end if it does happen. -RunningOnBrains^(talk) 01:49, 18 May 2012 (UTC)[reply]

The diagram sketches [1].--69.233.254.22 (talk) 02:35, 18 May 2012 (UTC)[reply]

Eclipse question

I've heard that there will be a partial solar eclipse in my area on Sunday, and I plan on watching it. What type of eye protection do I need? Thanks! 24.23.196.85 (talk) 05:59, 18 May 2012 (UTC)[reply]

Regular sunglasses aren't enough. I believe the usual precaution is not to look at the Sun at all, but rather look at a projection of the Sun. If you have no equipment for this, you can create a makeshift pinhole lens by poking a pin through a sheet of paper (preferably dark colored) and letting it shine on a white sheet of paper. StuRat (talk) 06:06, 18 May 2012 (UTC)[reply]

Welding goggles are sufficient protection if you can get your hands on them. There are a good number of eclipse-viewing goggles available online (I tried to link to amazon, but apparently even admins are blocked by the spam filter. How rude!), though I'd be sure I bought from a reputable vendor if I was going to risk my vision. Alternatively, it is safe to look at the sun for brief periods close to sunset ([2]); depending on where you are it may still be visible then. Just don't stare, and I'd still recommend sunglasses.-RunningOnBrains^(talk) 06:50, 18 May 2012 (UTC)[reply]

And it should be number 14 welding glass, not any other number. Sagittarian Milky Way (talk) 17:06, 18 May 2012 (UTC)[reply]

This construction or variants of it should give good results compared to other designs as it will (a) prevent stray light from hitting the screen, (b) reduce the loss of light from transmission through the screen. An adjustable back board(made by using one box inside another) will help you make the image-size brightness tradeoff. Use a binocular instead of the pinhole for better imagesStaticd (talk) 09:11, 18 May 2012 (UTC)[reply]

You can also get good projections simply by walking under some trees - pinholes in the leaves will project images of the sun (of varying focus) for a unique effect. Wnt (talk) 14:09, 18 May 2012 (UTC)[reply]

I was at Watford Junction train station at the time of the 1999 total eclipse, and was fortunate enough to see multiple images of the eclipse reflected off one of the dark glass windows of the waiting room! --TammyMoet (talk) 15:36, 18 May 2012 (UTC)[reply]

And in 2004 I didn't have a real filter, I saturated a piece of paper with butter, started looking through it for the shortest instant needed to form an image. Constantly blinked or waited 1 or 2 seconds depending on brightness. Was this bad? I stopped doing it when it when it seemed too bright (how high I don't remember but no more than about 12°). Another time I was holding eclipse glasses over 7x35 mm binoculars (the front, never the back), (I made a shield cause the glasses frames were too small), the sun was ~26° high, and either I put them up too late or probably forgot to cap the other lens despite planning to do that but holy crap, I saw sun! I shut my eyes as quick as I can. Thank goodness at least an eye doctor later didn't say anything (and I didn't ask). So don't do anything stupid/risky like this. They got so hot from the method above that a piece of glass broke off inside. Sagittarian Milky Way (talk) 17:57, 18 May 2012 (UTC)[reply]

What if you pointed a video camera at the eclipsed sun for 15 seconds or so (without looking through the view scope of course) and then watched it later on the TV? Obviously, the harmful rays would not be recorded and conveyed through the TV screen when you watched it, but the question is if 15 seconds pointed at the sun would seriously damage a video camera's CCD. 20.137.18.53 (talk) 15:43, 18 May 2012 (UTC)[reply]

Yes, I would expect that to damage the camera. Specifically, I'd expect the area of sensors which had the Sun focused on them to lose sensitivity. StuRat (talk) 18:13, 18 May 2012 (UTC)[reply]

That sounds a lot like electronics advice that should be given by a trained professional. ;) It seems worth saccing a videocamera for a total eclipse, but not an annular. ;) Wnt (talk) 16:54, 18 May 2012 (UTC)[reply]

Or get one of these, only $100,000 for the 95mm x 95mm CCD alone :) 20.137.18.53 (talk) 17:15, 18 May 2012 (UTC)[reply]

I suppose you could design a system where a camera has something like a "finder scope" that measures the max light level and puts the appropriate filter in front of the main lens. However, sudden changes in brightness, like the Sun coming out from behind the Moon, might still damage it. StuRat (talk) 19:23, 18 May 2012 (UTC)[reply]

Maybe a suitable photochromic lens material could be developed, like the one in those eyeglasses that become sunglasses outdoors? Which works too slow and too mild for this purpose. Even photographic solar filters transmit 0.01% of light, 10 times that of filters for eyes. Sagittarian Milky Way (talk) 21:49, 18 May 2012 (UTC)[reply]

An important thing to remember when picking a filter is that direct sunlight is a mix of infrared, visible, and ultraviolet light, any of which can cause eye damage. A lot of filters (eg. filters designed for cameras) only block visible light, leaving the infrared and ultraviolet components to blind you. --Carnildo (talk) 23:20, 18 May 2012 (UTC)[reply]

Thanks everyone, I used a #10 welding filter glass (couldn't find a #14) and didn't have any problems (but I did take the precaution of turning away whenever I felt my eyes start to get tired). 24.23.196.85 (talk) 05:00, 21 May 2012 (UTC)[reply]

Phd stipend life sciences

Please don't post the same question to multiple places. Your question will be answered at Wikipedia:Reference desk/Miscellaneous, section "phd salary". Nyttend (talk) 12:44, 18 May 2012 (UTC)[reply]

What's the most likely problem with my tire inflator/spotlight?

I have a tire inflator with spotlight from the same manufacturer but not the exact same model as this one. I can charge it with the AC adapter all night until the battery charge status indicators (as seen on the fourth page of the PDF) show full charge with two red LEDs and one green one. But after I unplug the AC adapter, within a few minutes, if I push the battery charge status pushbutton, only two red LEDs come on, indicating a supposed medium battery charge level. I opened the thing up after having fully charged it and seen the indication of only medium charge (when the adapter was unplugged). The thing has two 6V sealed lead acid batteries. I tested both with my multimeter every couple of hours for the past two days. One has maintained a level of 6.57V, and the other has maintained a level of 6.43V. What is the most likely reason I get only two red LEDs and not the green one when the adapter's not plugged in? 1) Something's wrong with the charge indicator circuitry, 2) Something's wrong with the batteries (are sealed lead acid batteries labeled 6V supposed to be getting up to 6.4-6.5V? do bad things happen when they are overcharged by this much?), or 3)something else (ideas appreciated)? Thanks. 20.137.18.53 (talk) 12:59, 18 May 2012 (UTC)[reply]

The article Lead-acid battery indicates that 2.1V per cell i.e. 6.3V from your battery is a normal open-circuit voltage at full charge. The slightly higher voltage that you measure is not likely any fault and a gelled electrolyte battery would happly accept continuous 6.7V float charging. There could be a calibration error in the green charge indicator or you may be using the unit at an unexpected temperature. 84.209.89.214 (talk) 14:23, 18 May 2012 (UTC)[reply]

about sodium silicate

Hi, I want to remove or de-active sodium silicate property from west water of textile unit. — Preceding unsigned comment added by 115.248.240.58 (talk) 14:37, 18 May 2012 (UTC)[reply]

What is a textile unit? Sodium silicate is soluble in a highly alkaline solution. Plasmic Physics (talk) 14:40, 18 May 2012 (UTC)[reply]

Sodium silicate is often shipped with clothes, to absorb humidity and prevent mildew. It's normally grains in a small packet. Are you saying the packet ripped open and the grains are on the clothes ? If so, just brush them off, they aren't toxic to the touch (but wash your hands after, as they can be alkaline, and you wouldn't want them to get in your eye). If they leave a residue, run it through the washing machine. StuRat (talk) 18:19, 18 May 2012 (UTC)[reply]

I think the OP is not a native English speaker, possibly third world, and meant to ask: "I want to remove or de-activate sodium silicate properly from waste water produced by a textile (manufacturing) unit. How can I do this?" Wickwack60.230.203.253 (talk) 04:03, 20 May 2012 (UTC)[reply]

Neutralize with acid and filter the residue. 24.23.196.85 (talk) 05:02, 21 May 2012 (UTC)[reply]

Gibbs free energy

Can someone explain what Gibbs energy is simply and give a biological example of Gibbs free energy. This article [3] is far too complicated. 176.250.232.230 (talk) 15:25, 18 May 2012 (UTC)[reply]

Simple explanations will invariably gloss over subtle details: this is tricky, because Gibbs energy is distinct from enthalpy and Helmholtz free energy, only by a small variation in definition. Roughly, Gibbs energy refers to the available energy from a chemical reaction, accounting for the pressure-volume work that must accompany that reaction. For example, if fermentation will release gaseous CO2, we use the Gibbs energy to quantify the work done, minus the "useless" work in expanding the CO2 as a gas. A worked example: ethanol metabolism thermodynamics. Nimur (talk) 15:47, 18 May 2012 (UTC)[reply]

thanks but people refer to Gibbs energy with things like linking amino acids to build proteins, converting ATP to ADP and the Krebs cycle and I just don't see the link with Gibbs which seems to be a thermodynamics concept rather than anything biological. — Preceding unsigned comment added by 176.250.232.230 (talk) 15:54, 18 May 2012 (UTC)[reply]

Lets try this really simply, by explaining "free energy" first. Free energy is energy availible to do work. Period. It just means that it is energy which could do something useful. There are forms of energy which are not free, that is there is energy which will cost you more energy to get to use. Roughly speaking, this is what entropy is. Basically, all of the energy in the universe is constant (First Law of Thermodynamics) but the amount of free energy is decreasing as the amount of entropy is increasing (Second Law of Thermodynamics). The different types of "free energy" and related measurements (like Gibbs Free Energy, Helmholtz Free Energy, Enthalpy) are just different variations on that theme; they are mathematical ways of expressing free energy in terms of highly constrained experimental set ups. One way to look at energy is to divide it into thermal energy and mechanical energy; that is energy which changed the temperature of a system, and energy which moves something around. So, free energy has a thermal component (changes in temperature) and a mechanical component (moving stuff). When you deal with gases, the mechanical aspect of their free energy deals with changes in volume (think, heating a balloon) and pressure (think, heating a steel tank). The difference between the various types of free energy is in how they treat that mechanical component of gases. In Gibbs free energy, your calculations assume that the system is at a constant pressure. For any system which is exposed to the earth's atmosphere, this works well, because any production or consumption of a gas will have a negligible effect on the entire earth's atmosphere, so any open container is a good Gibbs system. In Helmholtz free energy, your calculations assume a constant volume, which happens when you have a closed system, say a sealed tank, where the pressure will tend to vary a lot, but the volume remains constant. Gibbs free energy is also very important, because it is (via the Second Law of Thermodynamics) a mathematical way to calculate spontanaity. That is, any process which itself has a decrease in free energy associated with it will be spontaneous, because the universe spontaneously loses free energy, so any process that does that is likewise spontaneous. If you have a process which has an increase in free energy, TANSTAAFL, so there has to be a connected process which lowers the free energy by a greater amount, so the net change in free energy is always decreasing. So, to put it in simplest terms:

Free energy is energy which the universe has availible that you can tap into to do something useful
Gibbs free energy is a specific way of measuring that energy which works well in systems that are "open" to the environment
Gibbs free energy is important in calculating how "spontaneous" a process is; processes which cause a decrease in free energy occur spontaneously
(to your last question) Thermodynamics is inescapable. It's not like the laws of thermodynamics stop working in biological systems. That's why they are "laws" of the universe. They always work and continue to work, so when looking at, say, the assembly of a protein, if it has a negative Gibbs value, we know that it occurs spontaneously. This is kinda important info to know as a biochemist or molecular biologist who is concerned with how biological processes can occur.

Does this all help? --Jayron32 16:53, 18 May 2012 (UTC)[reply]

Thanks alot. That's a really good explanation. Most books or articles I look at just get too mathematical. — Preceding unsigned comment added by 176.250.232.230 (talk) 17:56, 18 May 2012 (UTC)[reply]

Zeta potential

I have a basic understanding of zeta potential (a property of colloidal systems). My question is, do hydrocolloids such as protein have a zeta potential? What about dissolved ions; do they have zeta potentials? ike9898 (talk) 18:48, 18 May 2012 (UTC)[reply]

Well, just trying the first example that came to mind, I searched "sickle cell" "zeta potential" and got actual numbers for red blood cells.[4] (also mentioned in Erythrocyte sedimentation rate). Trying the same for amyloid got what looked like a weaker set of results but nonetheless [5] [6]. My thought is that the measurement for proteins should be sort of weird because their aggregation depends so much on interactions that vary widely across the surface, but I really don't know. Wnt (talk) 19:00, 18 May 2012 (UTC)[reply]

Well, blood cells really don't fit into the category of things I am asking about. I'm taking about aqueous dispersions of hydrophilic polymers such as protein, starch, or polyacrylamide. Amyloid doesn't really fit into this category well, either. ike9898 (talk) 19:18, 18 May 2012 (UTC)[reply]

Apparently starch granules have a zeta potential. (Google dumps lots of results; apparently it's important for paper making) Polyacrylamide delivers more random results ... if it's a true gel, I don't know how you define a zeta potential, but that doesn't mean it can't be done. ;) Here's zeta potential for BSA [7]. Wnt (talk) 23:21, 18 May 2012 (UTC)[reply]

Thanks. The last sentence, especially, is a good lead. ike9898 (talk) 01:00, 19 May 2012 (UTC)[reply]

Flat universe have zero total energy?

I read from some dude on the internet (not exactly reliable) that the WMAP and Boomerang experiments (no idea what those are) indicate that the universe is flat and there is no net warpage of space time. Then he claimed that a flat universe can have zero total energy and thus come from nothing. What on earth is he talking about? Is this complete bs? ScienceApe (talk) 19:11, 18 May 2012 (UTC)[reply]

Those experiments (WMAP and BOOMERanG experiment) don't indicate that space is flat, they are simply consistent with it being flat. There is a margin of error in the results of any experiment, so all we can say is that zero curvature is within the range the experiments give. To conclude that it is absolutely flat, you need to use theoretical arguments, rather than experimental ones. --Tango (talk) 19:50, 18 May 2012 (UTC)[reply]

Check out Lawrence M. Krauss's 2009 lecture A Universe from Nothing. SkyMachine ⁽⁺⁺⁾ 20:52, 18 May 2012 (UTC)[reply]

Even theory doesn't imply that it's exactly flat, though I think the theoretical constraint is a lot stronger than the experimental constraint. -- BenRG (talk) 21:25, 18 May 2012 (UTC)[reply]

See Zero-energy universe. It's an idea that doesn't make much sense to me (because you have to break general covariance in order to talk about the energy of the universe), but plenty of legitimate physicists believe in it.

(Incidentally, the universe is spatially flat (approximately). Spacetime isn't flat.) -- BenRG (talk) 21:25, 18 May 2012 (UTC)[reply]

Can you explain what that means exactly? That the universe is spatially flat. ScienceApe (talk) 22:00, 18 May 2012 (UTC)[reply]

It means that if you look at the distances to all of the galaxies at a particular cosmological time (a particular era in their evolution), the number of galaxies within a distance R of you is proportional to R³. The number of galaxies would increase more slowly as R increased if space was positively curved, or more quickly if it was negatively curved. This is like measuring the amount of Earth's surface that's within a given distance of you—for small distances it grows like R², but the increase slows down for distances in the thousands of kilometers. The difference between spacetime and space in this context is like the difference between Earth and the surface of Earth. Earth is flat (it's a ball in 3D Euclidean space, approximately) but Earth's surface is positively curved on average. -- BenRG (talk) 23:08, 18 May 2012 (UTC)[reply]

Why isn't spacetime flat? If space is approximately Euclidean, isn't spacetime approximately Minkowski? I would call Minkowski spacetime flat - would I be wrong? --Tango (talk) 23:09, 19 May 2012 (UTC)[reply]

Yes, Minkowski spacetime is flat spacetime. However, even if the spatial portion

\mathrm {d} \mathbf {\Sigma } ^{2}

of the FLRW metric is Euclidean, the FLRW metric does not describe a flat spacetime, i.e. the FLRW metric is not equivalent to the Minkowski metric, unless the scale factor is constant. Red Act (talk) 14:59, 20 May 2012 (UTC)[reply]

Mootractor

For lack of a better name. I made this image in the hopes that I can make a collage of images for different views of the moon.

Can I assume that a view from the north pole would be 180 deg different from that of the south pole and 90 deg different from the equator? I am hoping that people from around the world can hold their monitors up to the moon and let me know which angle shows on the top of the moon, or is there a way to do this with math once I get one from the equator?--Canoe1967 (talk) 22:26, 18 May 2012 (UTC)[reply]

You might find Commons:Category:Moonrises and Commons:Category:Moonset to be useful (hmmm, the first two photos I looked at from each, both from Germany, had about the same angle, though one was rising and one setting. Thinking about the moon is a good way to strain your spatial comprehension. ;) File:Gaisberg_and_rising_full_moon.jpg File:Monduntergang_2011-04-17_002.JPG) Wnt (talk) 23:13, 18 May 2012 (UTC)[reply]

http://wms.lroc.asu.edu/lroc_browse/view/WAC_GL000 may be the same as a view from the equator. I may have to query further on an astronomy site.Canoe1967 (talk) 00:11, 19 May 2012 (UTC)[reply]

Resolved

My original plan won't work. The wise people on the astronomy site tell me that there are variations in rotation of up to 180 deg of view from any one point on earth from moonrise to moonset. Our view in the northern hemisphere would be close to 180 degrees sideways from that of the southern hemisphere. Now I just need a practical use for the mootractor image I made.--Canoe1967 (talk) 02:51, 19 May 2012 (UTC)[reply]