what does wein's law tell about the night sky?
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Firstly,there are several colors of stars, red, yellow, blue and white. The reason they are different colors is because they are hot, very hot actually. All matter emits radiation, peaking at a wavelength (which can sometimes be seen as a color) which is dependent solely on the temperature of the body. This is known as Wein's law (pronounced Veen's law). Another cool thing is about blackbody radiation, which happens to all objects regardless of it's temperature. Most objects we encounter in everyday life are somewhere around room temperature. \n\nAs an object grows hotter, there is, more energy being released. As the energy level of radiation is increased, the wavelength becomes shorter and shorter. When the human eye perceives different wavelengths of visible light, we interpret it as different colors. The coolest stars are around 3,000 degrees Celsius and they are red stars. Next are the orange/yellow stars which are about 6,000 degrees Celsius. After that at 10,000 degrees Celsius, you will see a green star, and finally a blue star is around 25,000 degrees Celsius.\nReasons we see different colors are because of our eyes. Special parts of our eyes pick up on certain colors. For example, Rods, which are located in the retina your eye and are more sensitive are very unresponsive to red light. Cones are less sensitive than rods and more clustered near the center of the retina. Three types; red, blue and green make up the 7 million cones in a human eye. Being less sensitive than rods, cones require many more incident photons of the right frequency to trigger them. This is the main reason why we do not see color at night.
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When the light from the sun hits the earth some of the light (The higher frequency or blue light) gets trapped or rather scattered by the smaller molecules in the atmosphere.  This scattering makes the sky blue because these particles reflect this blue light.\nAt night the light we are seeing is  the light of  the sun reflected off of the moon and it is much less intense.
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Well that's sort of subjective. A clear, cloudless night is likely to be colder, simply because clouds create sort of a "blanket" so to speak covering the ground from the most frigid of air. That's why desert nights can be so devastating. \n\nHowever, if you're talking about cloudless nights with or without stars, it makes no difference. One of the biggest reasons we cannot see the stars too well is simply light pollution. If we're near a city, the lights that go up reflect and block virtually all of the night's stars. \n\nSo basically, it's impossible for me to say beyond that without clarification.
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Well the simplest way has already been said... the sun rises in the east and sets in the west... so you can work out north from that.... \n\nBut as you mention the stars are we to assume you are trying to find direction at night?\n\nAgain there are many country ways - like the moss growing on trees and prevailing winds etc - but I personally wouldn't rely on this.\n\nSilly thought but if you have a map and can see any landmark or town lit up at night you can get your direction.
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The sky is blue partly because air scatters short-wavelength light in preference to longer wavelengths. Where the sunlight is nearly tangent to the Earth's surface, the light's path through the atmosphere is so long that much of the blue and even yellow light is scattered out, leaving the sun rays and the clouds it illuminates red, at sunrise and sunset.\n\nIndividual gas molecules are too small to scatter light effectively. However, in a gas, the molecules move more or less independently of each-other, unlike in liquids and solids where the density is determined the molecule's sizes. So the densities of gases, such as pure air, are subject to statistical fluctuations. Significant fluctuations are much more common on a small scale. It is mainly these density fluctuations on a small (tens of nanometers) scale that cause the sky to be blue.
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Sky and Telescope and Night Sky
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stars have a life span as well, they are born and they die. but these processes could take  millions and even billions of years to happen.they are also very very far away from us.\non a cloudless and moonless night, you may see that the sky is full of them. on a bright moonlight they seem to be less numerous. but on any given time there is about 4,000+ of them that can be seen by the naked eye. these is still true as it was since ancient times. the fact that you seem to see a lesser number of them may be due to the effects of bright city lights were you are living. bright ground based light have a dampening effect to star lights at they are viewed by the observer. if you want to see lots of them, i suggest that you go out far from the city where it is dark, provided the sky is not cloudy and that there is no moon in sight.
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The sky is blue because the nitrogen in the air scatters the blue light out of sunlight. \n\nOur sun is a yellow star, so it has slightly yellow light, but it is still pretty close to white light.\n\nSunlight on earth is slightly yellower than it is in space because some of the blue light in sunlight gets scattered out by the presence of nitrogen in the air, making the sky appear blue. So \n\n(White light) - (Some Blue light) = (Yellow light)\n\nAs the sun sets, the sunlight travels through more air, and the nitrogen scatters out more blue light and the sun appears first orange, and then finally red.\n\nAs the sun starts to set:\n\n(White light) - (More Blue light) = (Orange light)\n\nand finally as the sun has almost set:\n\n(White light) - (Lots of Blue light) = (Red light)
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Neither one actually blinks.  Satellites are visible at night because they reflect sunlight hitting them just like the moon does.  Stars emit their own light, but are hundreds of millions to billions miles away, and so the light from those giant suns looks like tiny pinpricks in our sky.\n\nThe blinking and twinkling of the lights of these bodies is due to shifts in the atmosphere.  Different temperatures of air and smog/pollution from cities create variations in the atmosphere that cause the light to bend, shift and warble on its way to us.  This tends to be more noticeable when observing stars because the relative size of the light source is so much smaller when you compare the percentage of the sky they take up.  A small patch of warm air passing between you and Betelgeuse can make it seem to blur and twinkle.\n\nSo either one can 'blink', but it's a quality of the atmosphere in between you and what you are viewing, and not a feature of the light coming from the object.
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STARS AND NEBULAE.\n\nMost of the things you can see in the night sky are stars: a few thousand are visible to the unaided eye. A star is a hot ball of mostly hydrogen gas; the Sun is an example of a typical, ordinary star. Gravity keeps the gas from evaporating into space, and pressure due to the star's high temperature and density keeps the ball from shrinking. In the core of the star, the temperature and densities are high enough to sustain nuclear fusion reactions, and the energy produced by these reactions works its way to the surface and radiates into space as heat and light. When the fuel for the fusion reactions is depleted, the structure of the star changes. The process of building up heavier elements from lighter ones by nuclear reactions, and adjusting the internal structure to balance gravity and pressure, is called stellar evolution. \nLooking at a star through a telescope can tell us many of its important properties. The color of a star tells us its temperature, and the temperature depends on some combination of the star's mass and evolutionary phase. Usually, observations also allow us to find the luminosity of the star, or the rate at which it radiates energy as heat and light. \nAll stars visible to the unaided eye are in our galaxy, the Milky Way. The Milky Way is system of roughly 100 billion stars, along with a great deal of interstellar material. The galaxy is shaped like a flattened disk embedded in a round, faint halo. Gravity keeps the stars from drifting away, and the motions of the stars keep the system from falling in on itself. The Milky Way has no distinct edge - the distribution of stars tapers off gradually with increasing distance from the center. The SDSS detects stars more than a million times fainter than can be seen with the unaided eye, far enough to see the outer structure of the Milky Way. \nStar Colors and Luminosities: The H-R Diagram\nAstronomers often make plots of the luminosities of stars compared to their colors. The first such charts were made in the early twentieth century, when astronomers took spectra of thousands of stars, then placed the spectra into a sequence based on the appearance of several different features. The classes of stars were given different letters as names; in order of decreasing temperature, they are OBAFGKMLT. The hottest stars are class O, while the coolest are class T. Two astronomers, Ejnar Hertzsprung and Henry Norris Russell, independently started to wonder what would happen if they compared stars' luminosities to their spectral classifications (or, alternatively, to their temperatures). They knew that some stars were hotter and more luminous than the sun, and that others were cooler and less luminous. Hertzsprung and Russell found that 90% of the stars fell into a narrow band they termed the "main sequence." Today, we call this type of plot a Hertzsprung-Russell (or H-R) diagram. \nAstronomers further divide each letter into ten categories from 0 to 9, with 0 being the hottest star in that spectral class and 9 being the coolest. So, a B1 star is hotter than a B2 star, and a B9 star is hotter than an A0 star. Our own sun is at the "hot" end of the G range with a surface temperature of 5,770° K; therefore, it's called a G2 star. \nSpectral classes give us a convenient way to refer to most types of stars - from O0, the hottest at over 25,000° K, down to T9, the coolest failed stars at 1,000° K. Each spectral type of star is associated with a specific color: all G-type stars like the sun are yellow, all M-type stars appear red, and all B-type stars are bluish. Thus, this system of letters and numbers tells us where a star is on the horizontal (color or temperature) axis of the H-R diagram. \nTwo alternative systems tell us approximately where on the vertical (luminosity) axis a star can be found. One system uses absolute magnitude, a measure of luminosity derived from the apparent magnitude, or brightness of the star
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The sky appears blue to us on a clear day, because the atoms of nitrogen and oxygen in the atmosphere separate the suns white light into its many colours, and scatter them throughout the atmosphere.The wavelength of the blue light scatters better than the rest, predominates over the other colours in the light spectrum, and makes the sky appear blue to us.The scientific name for this phenomenon is the Tyndall effect, more commonly known as Rayleigh scattering.\n\nThis phenomenon describes the way in which light physically scatters when it passes through particles in the earths atmosphere that are 1/10th in diameter of the color of the light. The light spectrum ranges in wavelength from red to violet, and, since the wavelength of the blue light passes through the particles with greater ease than the wavelengths of the other colors of light, the sky appear blue to the naked eye.\n\nThe human eye has three types of light receptors, known as cones, located in the retina. The cones are either considered to be red, or blue, or green, based upon their strong response to light at these wavelengths. As light stimulates these receptors, our vision translates the signals into the colors we see.\n\nWhen gazing at the sky, the red cones respond to the small amounts of red light scattered, and even less strongly to the orange and yellow wavelengths. Although green cones respond to yellow, their response to scattered green and green-blue wavelengths is stronger. Finally, colors near the strongly scattered blue wavelengths stimulate the blue receptors.\n\nIn short, the skylight stimulates the red and green cones almost equally, while stimulating the blue cones more strongly. For these reasons, our vision naturally adjusts as clearly as possible to separate colors.
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Twinkle twinkle little star\n\nThere aren't many nursery rhymes about astronomy. But 'twinkle twinkle little star' makes a useful point. We can tell which lights in the night sky are stars because they appear to twinkle. Planets, on the other hand, don't, they shine steadily in the sky.\n\nStars twinkle because they are very far away, and so appear as tiny points of light in our night sky. Some of this light is absorbed by moving air in the Earth's atmosphere, making the star appear to sparkle.\n\nPlanets, like Saturn or Jupiter, don't sparkle. This is because they are a lot closer to the Earth and so they look bigger in our sky than stars.\n\n\nThe Pistol Star is the brightest in the known Universe\n\nRather than being points of light, planets are small discs. As their light is more spread out, even if some of it is absorbed by our atmosphere, some of the light still filters through, so the planet doesn't twinkle. This means that you can tell the difference between a planet and a star without even needing a telescope, just by seeing if it twinkles!\n\nWeighing a star:\n\nAs for 'wondering what they are', starlight also contains an extraordinary amount of information that can answer that very question.\n\nWeighing a star isn't as difficult as it sounds as you don't need an enormous set of cosmic scales, just one equation. The more massive a star is, the more energy it gives off. So first of all, astronomers measure the star's 'luminosity', the rate at which it emits energy. Then they can work out its mass.\n\nMeasuring a star's temperature:\n\nOnce the mass of the star is known, you can calculate the temperature inside its burning core. Stars perform a delicate balancing act between gas pressure pushing outwards and gravity pulling inwards. Mathematical equations can be used to map this. Then by measuring the size and mass of the star, astronomers can calculate the temperature of the core.\n\n\nWhat's inside a star?\n\nEven more incredibly, just by looking at starlight astronomers can discover what a star is made from.\n\nThe light that we see is just one kind of radiation known as 'visible light'. Other kinds include X-rays, ultraviolet, microwaves, radio waves and infrared. Different stars give out varying amounts of these signals, known as their 'spectrum'.\n\nWhen measured, the spectrum appears as a series of bright and dark lines positioned at specific points or 'frequencies'. This is the blueprint of a star and provides a wealth of information about what is happening inside.\n\nAs elements are heated inside the star, they absorb and emit energy, creating a 'blip' in the star's spectrum. So the position and strength of these lines reveal what elements are inside the star. Stars are classified into 'spectral types' according to the shape of this spectrum.\n\nLooking back in time:\n\nAlthough time travel isn't physically possible yet, we can see back in time just by looking out into space.\n\nLight from the Sun takes 8 minutes to reach Earth. So we are seeing what the Sun looked like 8 minutes ago. Alpha Centauri, our nearest stellar neighbour, lags behind by 4.3 years. So, the further we look out into space, the further we are looking into the past.\n\nThe distance that light travels in a year is called a 'light year'. The furthest that astronomers have ever seen are about 12 billion light years away, from a time just after the Big Bang, when the Universe was just a baby.\n\nI hope this helps....\n\nDon
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The nitrogen and the oxygen molecules in the air have the right dimensions to scatter blue light, but other colors pass through with little problem. So this causes the sky to look blue. \n\n(whitish sunlight)-(blue light scattered)= (yellowish sunlight)\n\nAs the sun sets (or rises), the sunlight passes through more air, and more blue light gets scatted, so the sunlight looks closer to orange or red\n\n(whitish sunlight)-(even more blue light scattered)=(red or orange sunlight)
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A basic observable quantity for a star is its brightness. Because stars can have a very broad range of brightness, astronomers commonly introduce a logarithmic scale called a magnitude scale to classify the brightness.\nThe Magnitude Scale:\nThe magnitudes m1 and m2 for two stars are related to the corresponding brightnesses b1 and b2 through the equation:\nm1-m2=2.5(logb1-logb2)=2.5log(b1/b2)\nwhere "log" means the (base-10) logarithm of the corresponding number; that is, the power to which 10 must be raised to give the number. Because this relation is logarithmic, a very large range in brightnesses corresponds to a much smaller range of magnitudes; this is a major utility of the magnitude scale.\nThe preceding equation gives us a way to relate the magnitudes and brightnesses of two object, but there are several ways in which we could specify the brightness and this leads to several different magnitudes that astromers define. One important distinction is between whether we are talking about the apparent brightness of an object, or its "true" brightness. The former is a convolution of the true brightness and the effect of distance on the observed brightness, because the intensity of light from a source decreases as the square of the distance (the inverse square law). The apparent magnitude of an object is the "what you see is what you get" magnitude. It is determined using the apparent brightness as observed, with no consideration given to how distance is influencing the observation. Obviously the apparent magnitude is easy to determine because we only need measure the apparent brightness and convert it to a magnitude with no further thought given to the matter. However, the apparent magnitude is not so useful because it mixes up the intrinsic brightness of the star (which is related to its internal energy production) and the effect of distance (which has nothing to do with the intrinsic structure of the star).Clearly, a star that is very bright in our sky could be bright primarily because it is very close to us (the Sun, for example), or because it is rather distant but is intrinsically very bright (Betelgeuse, for example). It is the "true" brightness, with the distance dependence factored out, that is of most interest to us as astronomers. Therefore, it is useful to establish a convention whereby we can compare two stars on the same footing, without variations in brightness due to differing distances complicating the issue. \nAstronomers define the absolute magnitude to be the apparent magnitude that a star would have if it were (in our imagination) placed at a distance of 10 parsecs (which is 32.6 light years) from the Earth. I can do this if I know the true distance to the star because I can then use the inverse square law to determine how its apparent brightness would change if I moved it from its true position to a standard distance of 10 parsecs. There is nothing magic about the standard distance of 10 parsecs. We could as well use any other distance as a standard, but 10 parsecs is the distance astronomers have chosen for this standard. A common convention, and one that we will mostly follow, is to use a lower-case "m" to denote an apparent magnitude and an upper-case "M" to denote an absolute magnitude. \nNotice the very important point that I can determine the apparent magnitude m of a star simply by measuring how bright it appears to be, but to determine the absolute magnitude M the distance to the star must also be known. As we shall see, determining distances to stars is a quite non-trivial matter in the general case.You might think that introducing the apparent and absolute magnitudes would resolve ambiguities about what we mean when we refer to the brightness of a star, but there is a further complication. The brightness of an object (whether apparent or absolute) depends on the wavelength at which we observe it, as we saw clearly in the discussion of
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Not a simple question, but  this is two main reasons.\n\n1) Brightness of the Star Play a part.   Assume uniform Atmosphere.\n\n2) The Atmosphere also another part.  Assume stars of the same brightness.\n\n1)  Brightness of the Star Play a part.\nBrighter the Star, less likely the twinkle.   Look at the Moon, does it go Bink Bink?  Too Bright.\n\nBut Dimer stars, under the same Atmospheric conditions, may Bink.\n\n2) The Atmosphere also another part.\nThe Atmosphere is not uniform, look at the sky during the day, sometime, it clear blue,  and other time clouds mass abound.\n\nThe Atmosphere is like a thin soup, with some sliver of bread in it,.  using that example, when the Stars of the same brightness is in the Sky,  imagine when a sliver of bread blocks lightly one of the stars, thus one Bink, and another don't.\n\nIt Real life, Stars are not of the same brightness, and the Atmosphere is not always uniform.  making the issue complex.
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no the sky is no actually blue, have you noticed that at night you can see space? well thats because during the day the sun ray that come through our hemisphere are hitting against the massive amount of Ocean on our Earth, they do not reflect, but instead refract off the water molecules and transmit into the air, shooting all the way back up to our hemisphere, this gives us the sight of a blue sky.
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The sky appears blue due to the scattering of sunlight by dust particles in the air.\n\nSunlight is comprised of light in different wavelengths and can easily be split with a prism.  The dust particles in the air are of the right size that they scatter blue light preferentially.  As a result, we see the sky blue.\n\nThe sky is black at night simply because there isn't any blue light to be scattered.\n\nIncidentally, moonlight is yellow because that is the generally reflected colour off the moon's surface.  It is reflected light strongly in the yellow waveband. The yellow light is not affected by atmospheric scattering.