How do They Measure the Diameter of a Star?
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In order to measure the diameter of a star you really need three pieces of information about the star (1) distance (2) brightness (3) and color.\nStep 1: Scientists can figure out the total power output of the star by knowing its brightness at Earth and its distance. \n\nStep 2: Figure out the surface temperature. The universe really gave scientists a lucky break because stars are fairly predictable objects. What I mean is that, for most stars once a scientist know one property of the star they can generally figure out everything else they want to know about it. This is because stars behave like "black bodies". This is a physics term which describes how an object of certain temperature glows at different wavelength (thus influencing its color). Most ordinary matter resembles a black body (has nothing to do with being black, it's just terminology). You probably already have an intuitive understanding of this from your everyday experience. For example, when you heat up an object, at first it might start to glow red. And as it gets hotter it might start to glow yellow, blue, and eventually white. Because stars approximate black bodies very well, by knowing the color of the star scientist can figure out what its surface temperature is quite accurately. \n\nStep 3: Another great thing about black bodies is that, for any specific amount of surface area astronomers can predict exactly how much light it will radiate (hotter objects are brighter). And since they already know the temperature and the total brightness of the star they can figure out its surface area, and thus it's diameter :)
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join the 2 pointz frm da arc vit da radius.measure out da value of da angle forned here.then substitute da values 4 this formula:  2*pie*radius/da angle u measured\n\nhappy solvin!
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That's easy! You measure it with a tape-measure and a stopwatch! Next question.
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measuring device of some sort (scale, ruler, thermometer)
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The distances to stars closer than about 150 light years can be measured directly by use of parallax.  The position of the star against background stars is measured at times 1/2 year apart, and then it is a simple mathematical procedure to determine the distance (you have a side and two angles of a triangle--the angular distance the star appears to move at it's distance over 1/2 year equals 186 million miles-the diameter of the orbit of the earth).  \n\nStars farther than that cannot be measured directly.  But, by use of knowledge about how bright a star should be (on average) for it's spectral type (which loosely is governed by its mass) an estimate of its intrinsic brightness can be made, and then by looking at how bright it appears, it's distance can be estimated.\n\nCepheid variables are used, as well, but mostly to determine the distances to groups of stars and of other galaxies.  Incidentally, the North Star (Polaris, or Alpha Ursa Minor) is a cepheid variable.\n\nNovae and supernovae tend to have average intrinsic brightnesses, so their apparent brightness in, say, a distant galaxy, tells us (within limits) it's distance.\n\nRed shift is used for objects outside our galaxy because the amount of red shift within our galaxy would be extremely small (it increases with distance) if it were not totally overcome by the gravity of the galaxy.
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Divide 34 by PI...that will give you the diameter.\n\nDiameter = Circumference / PI
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Well, we look at the light and determine "this light is about a million years old." :-) Not really, but that's the general idea.\n\nFor galaxies of very large distance, we can determine how fast the galaxy is receding from us. The easiest way is the Doppler shift - we can see the galaxy (obviously) and therefore astronomers can determine how big it is, what type of stars must be in them, and therefore what color light we should see. However, the light is slightly redder than what models predict (and what nearby galaxies have). We can measure this "red shift", plug it into Doppler's equation, and determine how fast the galaxy is moving. (This is similar to how when a police siren passes you, it drops its pitch - and how much it changes is proportional to how fast the police car is going.)\n\nThen there's a nice relationship called Hubble's Law, which states that the farther a galaxy is from us, the faster it's receding. This is a consequence of the Big Bang, and indeed the constant in this equation must be the reciprocal of the age of the universe. So we can then estimate (within a few thousand years or so) how far the galaxy must be from us.\n\nFor closer galaxies, there are some other techniques. There are certain types of variable stars (stars that, every few hours or days, increase and decrease their brightness) that in order to be stable must vary between two known brightnesses. Of course the brightness isn't exact, but the average among the thousands of variables in a galaxy is very close to exact. Now when we measure brightness (actually, apparent magnitude) from Earth, we see stars dimmer if they're farther from us. But because we know the absolute magnitude of these variables, and we can measure their apparent magnitude, we can calculate the distance we must be for them to become this much dimmer.\n\nThere are actually a lot of techniques, which work better for certain distance ranges. Look up the "distance ladder" if you're interested.
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There's no way of checking (as of yet) to see if there are four billion stars.  They'll just have to take your word for it.  Its probably not that important to them anyways.\n\nBut you can check to see if the paint is wet.  You should never believe anyone 100% anyways.  That's how you become a fool.
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What is the radious or diameter?
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Use the micrometer caliper to measure the diameter of the copper wire. \nThe micrometer caliper is used to measure distances with more precision than a vernier caliper. It has a 0.5 mm pitch screw, this means that you read millimeters and half millimeters along the barrel. Every revolution of the ratchet knob will open the jaws a half millimeter. The sleeve is divided into 50 divisions corresponding to one hundredth of a millimeter (0.01 mm) each. To take a measurement place the object between the anvil and the spindle, grip the ratchet and turn until the object is lightly gripped, do not overtighten. The first part of the measurement is taken from the barrel, each division is 0.5 mm, note that the millimeters and half-millimeters are on opposite sides of the line. Next obtain the reading of the sleeve and add this value to the reading you obtained from the barrel. \n1. Obtain the reading when the surfaces of the anvil and the spindle are in contact. This is the zero reading of the micrometer caliper, it can be either positive or negative. Record the zero reading to 0.0001 cm.
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area = pi times the radius squared\n\nThe diameter is twice the radius.\n\nSo divide the diameter in two, square that and multiply by pi.
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you need to know the radius to answer diameter. \n      2\n     R =D  r to the power of two equals D\n\nR=radius D= diameter
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The distances between stars is quite large .The general convention of Kilometers or miles cannot be used due o the large numbers that we would have to deal with .\nLight is defined to have a constant speed of 299792458m/s . This number is precise to the last digit .The distance trvelled by light in a year can be found using this velocity\nthe distance would be 299792458*60*60*24*365= a large number suitable to denote lage distances \nwhen we say that the distance is 5000 ly we do not wait for light to complete the  journey .We determine distances using a different method and then use the above number to find th distance
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It is an approximate way of measuring how big or bright or heavy something is.\n\nThe term comes from the brightness of stars. The brightest star in the sky is Sirius and there are about another dozen almost as bright (Vega, Aldebaran, Betelgeuse etc) that are collectively known as first magnitude stars. Not quite so bright are the second magnitude stars (eg a coupl of stars in The Plough are 2nd Magnitude, and so on down to the 5th and 6th magnitude stars, such as members of The Pleiades, which are only visible to the naked eye on bright, clear nights. And then even fainter stars that can only be seen with binoculars or a small telescope or a huge radio telescope.\n\nThe point is that star brightness is described in categories, in bands, which share similar properties eg "only able to be seen when there is a full moon out" or "supernovae". And it doesn't need to be more precise than that.\n\nThe phrase "to the nearest order of magnitude" is used widely outside of astronomy to indicate an approximate idea of what to expect, eg "How big a fine will I get for a parking offence? £100?"\n\nThe questioner is wanting to be reassured it is not £1,000 but more like £50 - £150.
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The scientific method is to:\n\nObserve\nHypothesise\nTest\nAssess\nRepeat the process\nRepeat again... and again... and again... etc.\n\n>If you observe something occurring\n(eg. A shooting star falls towards the earth)\n>You Hypothesise for something to have happened \n(eg. that the star landed just over the horizon)\n>You test your hypothesis\n(eg. you travel to where the star appeared to fall)\n> You assesss whether the hypothesis was correct\n(eg. you could not evidence of something falling there)\n\nFrom this you can repeat the excersize until you get a correct answer.\n>observe: the star moved towards the horizon\n>hypothesise: the earth is round and so the star moved along a tangent to the earth, passing out of the atmosphere\n>test: ask someone further along the path of the star\n>Assess: the star dissapeared at a point over the horizon and did not land on earth. Therefore my hypothesis could be correct.\n\nAfter a valid hypothesis is concluded then it becomes theory... you would then go out and try to prove your theory... such as proving the world is round, or is there another reason the star dissapeared (it may have burnt up in atmosphere).\n\nAs you see... science is a lot of work.
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It's the same way that scientists look at all massive measures: density*volume.  The density (ie the number of stars per square lightyear) is assessed by counting the frequency of galaxies and the size of galaxies.  The mass of galaxies can be inferred by the speeds of rotaion, and the mass will give you an idea as to how many stars there are in the galaxy by looking at the average mass of a star.  Then you get a sense of how many galaxies are in a given volume of space.  They use this, and extrapolate from the size of space (set by the tenets of general relativity, the Big Bang theory, the red-shift observed speed of expansion, etc), and they can thereby infer how many stars there are in the universe.\n\nIt's like the mass of the earth.  We can't figure it out with 10 kilograms, or even 100 kilograms, but we can get an idea as to the magnitude of the mass.  With magnitude, i mean the number of digits to the left of the decimal place.  We call the difference between 10 and 100 "one order of magnitude," and the difference between 100 and 100,000 "three orders of magnitude."  Such scales are commonly used in science for things where exact numbers are impossible to get, but the range of magnitude is important.  Some such commonly known scales are the measure of sound in decibles, the Richter scale for earthquake power, and the pH scale for acidity.  With a pH of seven, one can infer that a liter of water has 3,344,000,000,000,000,000 hydronium ions per liter, whereas it only has 3,344,000,000,000,000 hydronium ions per liter at a pH of 10.  In these cases, the magnitude, rather than the exact number, is the matter of interest.\n\nIt's the same in counting stars.  We can't know the exact number of stars, especially since they constantly form and die--but we can get a pretty good idea as to the magnitude of the number by looking at stellar density and extrapolating the size of the universe.
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Probably just as big as it is now. Its diameter is 864,938 miles (109 times the size of Earth). \n\nThe sun is over 4.5 billion years old... so a billion years ago it was doing pretty much the same thing it is now. A lot of nuclear fusion going on. \n\nIt will stay the same size until it has used up its core hydrogen fuel, the star starts to fuse helium and eventually other elements. During this time the star will expand into a red giant or super-giant, becoming tens or even hundreds of times larger. Eventually, no more fuel will be available and the star will collapse under gravity to form a white dwarf star only a few thousand kilometres in diameter.