Wikipedia:Reference desk/Archives/Science/2007 July 3

= July 3 =

The Sun on the Horizon
Can anyone tell me why the sun apprears larger on the horizon when it sets?

Poplargrovegirls 00:31, 3 July 2007 (UTC)marpro123


 * I believe it's quite similar to the Moon illusion. You'll find a number of theories in that article. —Steve Summit (talk) 00:38, 3 July 2007 (UTC)


 * Yeah - I agree - it's very, very slightly distorted by the thicker atmosphere - but not enough that you could detect by eye alone. It's an optical illusion - the only serious debate is WHY it's such a good illusion. SteveBaker 01:02, 3 July 2007 (UTC)

thanks, links were very helpful. Always assumed it was the atmosphere but was told not so had to check out for myself. Poplargrovegirls 13:26, 3 July 2007 (UTC)

Itchy nose at dentist
Just been to dentist. Got itchy nose whilst lying there. Mentioned it to dentist. She said a lot of people get an itch nose whilst in the chair and she hadnt worked out why. Does anyone have any idea? —Preceding unsigned comment added by 88.110.40.127 (talk • contribs) 00:47, 3 July 2007
 * I've heard sunlight can make people sneeze. Maybe the bright lights at the dentist get you halfway there? -- Beland 01:01, 3 July 2007 (UTC)


 * THe itch was on the outside., but I suggested the lights. —Preceding unsigned comment added by 88.110.40.127 (talk • contribs) 01:07, 3 July 2007


 * I believe this is a psychological issue, that is Ionlywantodothisthingwhenicant Syndrome. It's the same thing that causes your underwear to bunch up the second you leave the house, that gives you gas when you're in polite company, and that makes you hungry thirty minutes after your nonstop cross country flight departs --ʇuǝɯɯoɔɐqǝɟ 02:12, 3 July 2007 (UTC)


 * Interesting, I never really thought about it like that. Is there a psychological term for this broad experience?  And an article, hopefully?  Someguy1221 02:33, 3 July 2007 (UTC)


 * Well, besides the scientific Ionlywantodothisthingwhenicant Syndrome, there is the common name: Sourgrapsitis. --ʇuǝɯɯoɔɐqǝɟ 03:03, 3 July 2007 (UTC)


 * This might also be related to bread always landing buttered side down, see Buttered cat paradox for the sum of Wikipedia's knowledge on that topic --ʇuǝɯɯoɔɐqǝɟ 03:08, 3 July 2007 (UTC)

In addition to the factors mentioned above, I suggest that the dental work itself stimulates nerves in the face: the various bits of powered equipment tend to vibrate, and the dentist's hands are moving close to your skin. A mild stimulation could easily be felt as an itch. --Anonymous, July 3, 2007, 04:18 (UTC).


 * So could this be the same thing as only needing to rub your itchy eyes when you have your glasses on? Or is it that you do these things normally unconsciously, but when you cant or shouldnt, you start to notice it?

--88.110.40.127 11:28, 3 July 2007 (UTC)


 * Yes, I think that hits the nail on the head. Normally, when you have an itch ... you scratch it.  It is such an inconsequential and trivial event, that you don't even think twice about it.  It is almost a reflex.  However, when you cannot scratch the itch or you are prevented from doing what would be a natural relfex, then you notice the "event" that much more.  (JosephASpadaro 22:04, 3 July 2007 (UTC))

Space tracking networks
Does anyone know what the difference is between SPACETRACK and the United States Space Surveillance Network? -- Beland 00:52, 3 July 2007 (UTC)

Negative buoyancy
Is it true that some people have what is known as Negative buoyancy (ie they do not float in water). there doesnt seem to be a page on this. —Preceding unsigned comment added by 88.110.40.127 (talk • contribs) 01:06, 3 July 2007


 * I don't remember if this is the actualy term, but yes, many people cannot attain a "natural" floating position in the water. A lot of it depends on your body height and shape and your fat content (muscle and bones are going to be less buoyant than fat).  A lot of people simply cannot achieve an "ideal" floating position on top of the water--instead, they will have shift their body position (for example, raising the hands up slightly).  –Pakman044 02:36, 3 July 2007 (UTC)
 * If one is more dense than water (as the question suggests "they do not float in water") then limb position or other shape-changes won't help. However, muscle/bone/fat composition differences can explain why certain body parts sink vs float for various people. Further, since one's body is all joined together, one can take advantage of different buoyancies of the parts to raise or lower other parts by bending etc. From experience, "sinkers" are often not that far from being able to float—a deep breath is enough, kinda like swallowing a life vest. DMacks 05:17, 3 July 2007 (UTC)
 * Some of us Wikipedians are pretty dense, as should be obvious from our posts...169.230.94.28 03:11, 4 July 2007 (UTC)


 * When an object sinks, it is because it is more dense than the fluid it is in. This would still be called buoyancy, since it operates on the same principle (i.e. differences of density between an object and a fluid).  That is why we do not have (and should not have) an article called negative buoyancy. Nimur 03:41, 4 July 2007 (UTC)

I believe that there is a term for "negative buoyancy" — sinking. --69.177.208.125 23:39, 8 July 2007 (UTC)

Dimples on back of thighs
My girlfriend ( White,37,3 children,good health) is upset with what appears to be "dimple's" on the back of her thighs (1 ea. side) about mid point slightly to the outside of the muscle.To me it looks as if a tendon or maybe sinew is holding that part of the muscle back, thereby giving it a dimpleing effect is that possible? -shredder0288
 * Cellulite? DMacks 05:18, 3 July 2007 (UTC)
 * Sounds similar to dimples of Venus. If there's only one on each side, and they're symmetrical, it's unlikely to be cellulite.  --TotoBaggins 06:00, 3 July 2007 (UTC)

rays that reflect by bones
Neel shah556 06:21, 3 July 2007 (UTC) hi i would like to know which rays get reflected specifically by bones only and not reflected by metals as well gases Neel shah556 06:21, 3 July 2007 (UTC)neel shah556


 * Xrays can be scattered from bones, but metals are going to reflect or scatter these too. Bones contain Calcium which is a metal of moderate density.  You may be able to find a nuclear magnetic resonance frequency for something in the bone, but this is hardly a ray. GB 09:54, 3 July 2007 (UTC)


 * Gamma rays of around 10.3 Mev are absorbed and reemitted by Ca40 neclei. This should be very specific for detecting calcium, and should penetrate through other meterials very deeply.  The frequency will have to be controlled to about 1 part in a million to actually work. see Nuclear Resonant Absorption of Gamma Rays by Ca40.  However this is quite hazardous to living things nearby! Another method is to irradiate with neutrons and observe the gamma ray emmissions: eg 48Ca(n,y)49Ca,  emits 3.084 MeV y-rays.  This too would be hazardous. GB 01:41, 5 July 2007 (UTC)


 * Yet another technique is to use X-ray diffraction to detect tha apatite crystals in bone. The object is irradiated by a thin beam of xrays at a particular frequency.  The crystal planes in the minerals in the bone will reflect the X-rays at particular angles that are characteristic of the mineral content.  The 002 plane produces the biggest reflection.  See  for an experiment.


 * X-ray fluorescence is another way to go. Kα1,2 at 0.3359 nm for Calcium, Kα3,4, or Kβ1,3are names of spectral lines that could be used. GB 02:35, 5 July 2007 (UTC)

Denoting Free radicals
I noticed that Wikipedia just uses a full stop in chemical equations to denote a free radical. I have always seen the dot central and right of the atom. As long as it is right, does it really matter where the dot is placed? Thanks in advance. GizzaDiscuss  &#169; 06:29, 3 July 2007 (UTC)


 * It seems that both is used. In TeX a full stop is used: $$Cl_2 \overset{h\upsilon}\rightarrow Cl^. + Cl.$$, but in text a dentral dot is used: 2Cl·→ Cl2. Infact in that TeX both are used, a . and a superpostioned.
 * Are these different or should it be fixed? 213.48.15.234 08:23, 3 July 2007 (UTC)


 * Thank you for your response! Just wondering, how did you type the central dot? I can now Copy & Paste it when I need it but I'm still curious. Incidentally, I want to add a couple of equations where radicals are involved to some Chemistry-related pages on Wiki. GizzaDiscuss  &#169; 08:58, 3 July 2007 (UTC)


 * Copy and paste is exactly how i did it *hides*. Windows Character map says you can make it with Alt+0183. ··. Yup it works! I believe that it's also emboldened in the article, otherwise it's faint. ·. There we go :) 213.48.15.234 09:10, 3 July 2007 (UTC)

question
i have this bio quiz i have to answer i got from a pal.i eat with my head upside down.my mouth held horizontally beaneath the water.what am i? 2.i got a pirated cd of hitman 2 silent assasin.i reached the second last level of the mission.which is st petersburg revisited.the problem is that my gun is firing blanks.it has no effect when i shoot someone.is it possible that that is a defect because i got a pirated disc.or that the guy who made the cd edited it so that someone doesnt complete the game.


 * 1. A Flamingo? 2. We can't help you with pirated games. I doubt that the guy you bought it off of "programmed" the bug into the game. Buy the game from a reputable store if you wish to avoid these issues and recieve support form the publishers/developers. 213.48.15.234 08:20, 3 July 2007 (UTC)


 * My job is as a game developer - playing pirated ("stolen") games is a bad thing - it makes it harder for me and my colleagues to make a living - there are fewer jobs out there and they don't pay as well because of people like you. My family is worse off because of you and that hurts.  We games programmers are just regular guys - you'd like me if you met me - and I KNOW you appreciate the work that we do - because without people like me, you'd be playing one of the 60 different OpenSourced versions of Tetris or something. So why are you making my life worse?  I feel pretty strongly about this - and I now know your IP address because you handily left a record of it when you posted your question.  I have a clear confession of guilt from you - so this is going to be an open-and-shut court case.  I have pretty good computer skills - you are a self-confessed criminal - how about I see if I can trace your account and find a way to have a policeman knocking at your door tomorrow morning?  I'd tell you how much you can expect to pay in fines - and how much jail time you might serve - but we're not allowed to give out legal advice here on the Wikipedia help desk.


 * No - I'm not really going to do that - but then you're going to promise me you won't play pirated games anymore. Or maybe I'll just figure out your parent's email address. SteveBaker 11:49, 3 July 2007 (UTC)


 * Steve, while you're at it, port something to linux so I have something to play other than 60 different open source versions of Quake. Or hell, anything that isn't an FPS. Can we get a platformer or an action puzzle game (Zelda/Metroid style), pretty please? --ʇuǝɯɯoɔɐqǝɟ 13:01, 3 July 2007 (UTC)
 * I'm a huge Linux enthusiast - heck, I'm the guy who wrote TuxKart. I also wrote "Tux the Penguin - A quest for Herring" - which was the first 3D game ever designed for Linux.  It was a platformer - but sadly, not enough people wanted to help out on it (actually, aside from a guy who contributed some music - I got zero help on either project).  A 3D platformer is a big project for just one person - so it didn't really get properly finished.  TuxKart was much easier and is a really fun go-kart racing game.  But to answer your question - commercial games companies just can't afford to do Linux ports - there is no money in it.  Too many Linux users have dual-boot machines and they tend to rush out and buy the Windows version of a new game before there is time to port them to Linux - as a result, on the rare occasions when people like ID and Loki produced Linux ports, they sold really badly.  It doesn't help that in the months it takes to do the port, the Windows version has fallen from gamer favor and can be found in the $10 outcast bin right at the time when the Linux version is selling for $40.  The only way to avoid that and to create a market for Linux ports would be to release the Linux version on the very same day as the Windows version - but that would require serious investment in time and money at the very point in the game's development when both things are at a premium.  Right before a typical launch, the entire game team are likely to be working 'crunch time' - 60 to 80 hours a week - typically without overtime pay.  To expect them to crunch the Linux port at the same time is asking too much.  It's a hard problem to fix - for Linux games to be cost-effective there has to be a large pool of dedicated Linux-only gamers...but that can't happen because there aren't enough good Linux games out there. SteveBaker 16:04, 3 July 2007 (UTC)


 * The OP/thief doesn't have to take Steve's word for it, either: take it straight from MC Double Def DP, the Disk Protector.   --TotoBaggins 16:20, 3 July 2007 (UTC)


 * For the second question, it's the game design. The rifle is filled with blanks for a reason... Splintercellguy 18:58, 3 July 2007 (UTC)

jeez steve.first of all i wasnt scared one bit.its seems u have a really cool job and that my buying pirated games really pisses u off.only thing i can tell u is that its a tough world.survival for the fittest.as for getting my parents ip address,i dare u.am a software engineer student and unless telepathy is a course u took i think ur bluffing.but seriously al try and buy more genuine software next.just because u seemed so offended


 * Well, if you are a software engineering student (I was a Computers & Cybernetics student - essentially the same thing) - you should be more aware than most of how this problem will eventually hurt you, personally. You may not end up being a games programmer - but you will almost certainly be be spending a large chunk of your life writing software - and the odds are good that people will be pirating whatever it is you write.  That's going to have a direct effect on how much money you'll earn - how hard it'll be to find a job - how interesting that job will be - how secure that job is going to be.  The games business isn't the massive money making machine most people think it is - games programmers work longer hours than most software engineers - and we don't typically get paid overtime for doing it.  Sure, it seems a pretty glamourous activity - but most of the time it's not (I spent the last two days tracking down a shader compiler bug in nVidia's 8800GTX graphics drivers - it doesn't get much less glamorous than that!).  But to find that many of our biggest fans are prepared to screw us out of our (rare!) well-deserved successes is REALLY frustrating.  You're right about survival of the fittest - and in a world with much piracy that means that the companies that churn out large quantities of low grade junk are going to be the ones that make it.  Survival under this kind of pressure means not aiming aiming high.  So if people continue to pirate at the rate they are, the best people will move out of the industry - and those that stay will have less time and resources.  Game quality will suffer first.


 * It's not like the music business. It costs almost the same amount of money to record, produce, advertise and distribute a crappy piece of music as it does a great one - and only a very tiny share of the cost of a music CD is actually paying the musicians - so the record companies don't respond to falling income by reducing quality.  Not so with games - our costs are in a hundred or more people working for two or three years on one single title.  You can produce a crap game with a much smaller team in much less time so if we don't make enough profits to support that large team - that's exactly what you'll get.


 * Anyway - this is as much about your future as it is mine. (And if you don't think an old school hacker can find you from your IP address and contextual clues...you need to take some more networking courses!) SteveBaker 17:05, 4 July 2007 (UTC)


 * Nameless IP guy, I couldn't tell a TCP from a UDP, but I could still easily track you down. Steve knows his crap very well, I wouldn't tempt him. You'd do well to follow his advice, as well. I know how nice it feels to get all the games you want for free, but you're really just screwing yourself out of future jobs, not to mention there's a ton of free games out there, and I'm not talking about the above mentioned open source tetris variants. If you want some links to free games, leave a note on my talk page, and I'll get back to you --ʇuǝɯɯoɔɐqǝɟ 21:34, 4 July 2007 (UTC)


 * First question looks like a whale that eats plankton.Polypipe Wrangler 00:39, 6 July 2007 (UTC)


 * Steve while I appreciate how you feel, bear in mind it's not a criminal offence in every country to simply use a pirated copy of a product. It may simply be a civil matter. (IP 62.24.99.165 appears to be Kenyan, no idea what the legal situation there is) Also, at least you get to use a GeForce 8800GTX... :-P I'm still stuck with my 6600GT. Also the one person I know who took software engineer (who was a top student) in Malaysia career has been in the consultancy (implementing various projects for others) and large company IT department areas. While there is software programming going on I believe, it's not so much the kind of stuff that is sold. I would presume this is fairly common in Malaysia since there are AFAIK few local companies who write marketed software product. While piracy will still have numerous effects, I'm not so sure whether's your description accurately encompasses the work that many software engineer graduates end up doing (but then again, I don't really understand the field well) Nil Einne 00:02, 11 July 2007 (UTC)

radiology
is there any frequency of x-ray that is not refleced by metals203.187.197.27 09:49, 3 July 2007 (UTC)


 * No, unless the metal is beryllium. 213.48.15.234 10:18, 3 July 2007 (UTC)


 * Light metals will have little imapct on X-rays, because there are few electrons in each atom. Lithium and sodium magnesium and aluminium are other light metals, with lithium by far the lightest, floating on water. GB 05:48, 4 July 2007 (UTC)
 * I wonder if this this question is related to the "rays that reflect by bones" question from earlier today. Is there some more general problem you're trying to solve here (i.e., what's the context for the question)? DMacks 05:56, 4 July 2007 (UTC)


 * No. Part of what makes a metal a metal is the large (~1023/cm3) concentration of relatively free electrons. An incident electromagnetic wave causes these electrons to oscillate at its frequency, and reflection is observed at the angle at which all of these oscillations add constructively. Within a few skin depths, essentially no intensity is transmitted. X-ray reflectivity needs some work, but it does show how reflectivity depends on electron density. Higher frequencies and lower electron concentrations lead to greater penetration, and many devices have a thin "beryllium window" which contains the sample but is essentially transparent to high frequency x-rays. Of course, if this is related to that earlier question, one must consider that beryllium is toxic. -Eldereft 06:15, 7 July 2007 (UTC)

Interconnectivity of Earth's Food Web between Oceans and Land
Perhaps this is speculation more than science, per se, but how dependent are Earth's Oceans on land based life? If, say, all life on land including plant and animal were wiped out completely by something other than nuclear warfare or cosmic impacts(That is to say, no nuclear fallout or dangerous amounts of dust in the atmosphere or anything like that to factor in) how would Earth's oceans fare? I once heard that Earth's oceans produce and consume about the same amount of oxygen, and I can't think of many oceanic lifeforms that would require a food source from land. One problem I would see would be rampant erosion of huge rivers of mud rolling into the oceans. Perhaps problems could come from estuaries where land-based food for oceanic-life causing some kind of domino effect? Or would Earth's oceans be more or less uneffected? --Demonesque 09:50, 3 July 2007 (UTC)


 * Clearly there would be some niche species that would suffer greatly - there must be some that rely on nutrients washed out of river esturies and such. The balance of some populations might swing wildly due to lack of predation from birds, penguins, seals, etc - and that would undoubtedly start a number of boom/bust cycles that would probably kill off some populations - but boost others.  But other than that, I think ocean life would survive quite well.  After all, life on earth started in the oceans - at that time, the land was completely barren.  The lack of human activity - pollution and over-fishing in particular would clearly be of immense benefit to species that are in steep decline right now.  So I think the oceans would change - but not drastically. SteveBaker 11:30, 3 July 2007 (UTC)
 * The Oceans need nutrients from the land masses to sustain life, much of those nutrients come from life forms living on land or on their effects on the nutrient cycles, two factors greatly limit oceanantic life Iron and nitrogen. Only bacteria and maybe some fungus can free up nitrogen for use by other life forms. Land plants also have an effect of global temperature, higher air temperature would result in higher ocean temps resulting in a change in water chemistry.Hardyplants 02:18, 4 July 2007 (UTC)

Geodesic distance
I am trying to find out, what the geodesic distance in a Robertson-Walker-metric is. I came across comoving distance and proper length and I wonder if one of them is the thing I am looking for. The proper length looks quite nice but unfortunately the definition does not seem to be restricted to geodesics. (I wonder if such an arbitrary looking definition makes sense anyway.) I just found that it says "For instance, if one measured the distance along a straight line or geodesic between the two points, one would not be correctly measuring comoving distance." in comoving distance. So it looks as if both of them do not help me, do they? Anyway, can I use Riemannian normal coordinates to calculate the geodesic distance? Or would you propose another ansatz? -- 217.232.40.21 16:13, 3 July 2007 (UTC)
 * This may get better responses at the Mathematics desk... Nimur 16:35, 3 July 2007 (UTC)
 * Have you read Friedmann-Lemaître-Robertson-Walker metric? SteveBaker 18:52, 3 July 2007 (UTC)
 * Yes, I have. I would not ask if I was satisfied with the information provided there. It is kind of vague in this point, talking about "physical distance to a point in space at an instant in time" which says nothing about what the meaning of this distance is. As there are different notions of "distance" I did not assume this "physical distance" identical to the geodesic distance. -- 217.232.40.21 19:54, 3 July 2007 (UTC)

welding..........
can we arrange the welding processes ; smaw,fcaw,gtaw,gmaw & saw according to criteria; i tried based on knowledge of books but could arrange for few criteria that too not all processes.59.92.11.37 16:18, 3 July 2007 (UTC)
 * 1) quality
 * 2) field welding
 * 3) energy efficiency
 * 4) automation&
 * 5) out of position welding


 * For reference, we have articles on SMAW, FCAW,  GTAW, GMAW, SAW, and welding.  Nimur 17:00, 3 July 2007 (UTC)

breathing a bug accidentally
hi guys, i just breathed a bug...it may be inside my lungs... uh...besides it being gross...is it really dangerous? should i b worried?
 * You seem to have survived well enough to type the question. Generally, an insect of average size should not be dangerous if swallowed or inhaled, but if you feel any weird symptoms, you might consider getting it checked out by a doctor.  ◄   Zahakiel   ►  18:46, 3 July 2007 (UTC)


 * Well, we aren't allowed to give medical advice - but my best guess is that if you aren't coughing and choking really hard then you probably swallowed it - so it's in your stomach - not your lungs. Bugs make perfectly good food - so you should be OK.  But if you are in any way concerned or distressed - consult an expert - not Wikipedia. SteveBaker 18:48, 3 July 2007 (UTC)


 * You should check out the article on eating insects. They are an excellent source of protein. Lanfear&#39;s Bane

If it was inhaled, I'd suggest risk of Bronchopneumonia. See Pulmonary aspiration and consult your GP. --Seans Potato Business 20:39, 8 July 2007 (UTC)

How do we know the universe is expanding/accelerating if red shift increases with distance (time)?
Something that has always confused me is Hubble's explanation of red shift observations. The fact that distant objects were moving away from us more quickly than near objects is used as evidence of an accelerating expansion of the universe. This seems to me to be evidence of the exact opposite - that expansion is slowing. Looking at an object 2 billion light years away is looking at light that is 2 billion years old. This suggests that: a) we are now moving quickly away from the point where that star was 2 billion years ago, and/or b) the star 2 billion years ago was quickly moving away from the spot we are at now. These are, of course, equivalent propositions.

What confuses me about this being used for an accelerating universe is that it tells us nothing about how we are moving relative to that object now. In fact, relativity demands that I can know nothing at all about that object now, including its current speed relative to me. For all I know, in the 2 billion years since the light left that object, gravity could have slowed and/or reversed that expansion.

Could someone please help me to understand this better? Kurt 21:18, 3 July 2007 (UTC)
 * Part of the article on Hubble's law addresses this. You might also find Olbers' paradox interesting in relation to a finite / infinite universe and redshift. Lanfear&#39;s Bane


 * The problem is that it's hard to visualize the 3D space. So simplify it and think of the surface of a balloon.  All the stars are on the surface.  It starts inifinitely small and starts to inflate.  There is no "center" or "spot" on this perfect inflating balloon.  All the stars are moving away from all the other stars.  At any given time, the farthest stars have moved away the farthest amount in the same time.  By moving farther in the same time, they are moving faster.  therefore the farthest stars are moving away the fastest.  Turn it around and the fastest stars are the oldest and furthest away.  --Tbeatty 05:26, 4 July 2007 (UTC)


 * In fact this even works in one dimension. If you draw some equidistant points on a line, then assume this line is being stretched at a constant rate. Choose one of the points as Earth, and you'll see the other points move away with speed proportional to their distance. Move to another point, calculate the speeds and you'll see the same thing. This also demonstrates the point that although things are expanding in all directions from Earth, that doesn't mean there is anything special about our place in the Universe. Cyta 07:06, 4 July 2007 (UTC)


 * Note that the red shift just tells us that we're moving away from the object (or vice versa). It doesn't say anything about acceleration. To ascertain that you'd have to see if the amount of red shift changes. See also Accelerating universe. DirkvdM 10:11, 4 July 2007 (UTC)
 * Yes, but we already have that information. Or rather, the theory gives us that information.  The objects furthest way, and the most primordial objects, have the most red shift.  The furthest objects are moving away the fastest.  --Tbeatty 09:03, 7 July 2007 (UTC)


 * Kurt - you have asked an excellent question, which highlights some on the inconsistencies in the standard simplified explanation of the cosmological redshift. Here is a more "sophisticated" explanation. When measuring cosmological redshifts of distant galaxies, it is not the redshifts themselves that are of interest - it is what they tell us about the Hubble paramater, which measures how space itself is expanding. The amount of the redshift is determined by how much the Universe has expanded since the light that we observe now was emitted by the distant galaxy. This is, in turn, determined not just by the value of the Hubble parameter now, but by how the Hubble parameter has changed while the light was travelling. Accurate measurements of redshifts at different distances tell us how the Hubble parameter has changed over time, a change which can be measured by a value called the deceleration parameter (note that cosmologists always expected the Hubble parameter to change over time - they expected it to be getting smaller, as the expansion rate of the Universe slowed down). These accurate measurements are complicated by the following factors:
 * You need to measure redshifts of many galaxies at similar distances in order to average out the redshift components due to peculiar velocities, which we are not interested in.
 * You need a measure of distance that is independent of the redshift measurements themselves - otherwise you have a circular argument.
 * Recent measurements have shown that the deceleration parameter is negative, so the expansion rate of the universe is, contrary to expectations, accelerating. Gandalf61 11:23, 4 July 2007 (UTC)