how come (on TV) pictures of planets and other things have no stars in them.?
339062
Ak47 got it.\n\nWhen you see a picture of say, Saturn taken by the Cassini spacecraft, the camera's exposure is optimized for viewing the planet, not the background stars.  A longer exposure would show the stars, but wash out the planet.
937717
A lot.  Only 1% or less of the light actually makes the image.  This is why digital photography is so much better when it comes to astronomy.
1046132
A star produces it's own light, a planet does not, it merely reflects the light of the star. Because a star producing it's own light, it will glow brightly, dim, then glow again........this is the twinkling effect, much like the flame from a match, or any burning fire. :)
1165410
Ugh I cannot believe people actually ask this retarded questions.\nTell you what sparky, go outside at night, when there are plenty of stars. Now, take a picture of a friend with a flash or using an external light (as they did on the moon) Know what you'll find when the photos come back? NO STARS!\nWhen you understand what FOCAL LENGTH means, you'll know why the photos on the moon have no stars in them. I hope the website helps you understand...
496226
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
752575
The scientific name for the twinkling of stars is stellar scintillation (or astronomical scintillation). Stars twinkle when we see them from the Earth's surface because we are viewing them through thick layers of turbulent (moving) air in the Earth's atmosphere. \n\nStars (except for the Sun) appear as tiny dots in the sky; as their light travels through the many layers of the Earth's atmosphere, the light of the star is bent (refracted) many times and in random directions (light is bent when it hits a change in density - like a pocket of cold air or hot air). This random refraction results in the star winking out (it looks as though the star moves a bit, and our eye interprets this as twinkling). \n\nStars closer to the horizon appear to twinkle more than stars that are overhead - this is because the light of stars near the horizon has to travel through more air than the light of stars overhead and so is subject to more refraction. Also, planets do not usually twinkle, because they are so close to us; they appear big enough that the twinkling is not noticeable (except when the air is extremely turbulent). \n\nStars would not appear to twinkle if we viewed them from outer space (or from a planet/moon that didn't have an atmosphere). \n\n\n---------------------------------------------------------------------------------\nStars, except for the Sun, although they may be millions of miles in diameter, are very far away.  They appear as point sources even when viewed by telescopes.  The planets in our solar system, much smaller than stars, are closer and can be resolved as disks with a little bit of magnification (field binoculars, for example).\n\nSince the Earth's atmosphere is turbulent, all images viewed up through it tend to "swim."  The result of this is that sometimes a single point in object space gets mapped to two or more points in image space, and also sometimes a single point in object space does not get mapped into any point in image space.  When a star's single point in object space fails to map to at least one point in image space, the star seems to disappear temporarily.  This does not mean the star's light is lost for that moment.  It just means that it didn't get to your eye, it went somewhere else.\n\nSince planets represent several points in object space, it is highly likely that one or more points in the planet's object space get mapped to a points in image space, and the planet's image never winks out.  Each individual ray is twinkling away as badly as any star, but when all of those individual rays are viewed together, the next effect is averaged out to something considerably steadier.\n\nThe result is that stars tend to twinkle, and planets do not.  Other extended objects in space, even very far ones like nebulae, do not twinkle if they are sufficiently large that they have non-zero apparent diameter when viewed from the Earth.\n-------------------------------------------------------------\n\n\nI can be more specific, sure. Remember that just like a computer screen, your eye is composed of a certain number of "pixels," each represented by a single light-receptor cell in your retina. If two (or more) points of light are close enough such that they are focused on the same receptor cell in your eye, you will experience them as a single point of light. This is referred to as the "resolution" of your eye, or any telescope for that matter. \n\n\nNow, a star on the sky is in a true sense a single point of light. All the light comes through the atmosphere in exactly the same direction, through exactly the same atmospheric turbulence, and thus is bent in exactly the same way. So when it gets to your eye, the amount of light you see coherently varies. It also strikes (primarily) only a single receptor in your eye. \n\n\nOn the other hand, light from a planet is different. Each of a few receptors in your eye sees a large number of light rays coming f
809888
All stars are round, and there are many trillions of stars, although you can only see about 3,000 of them at any one time without a telescope. The sun is a typical star, only much closer than all the others.
141087
mainly :\nstars generate light, planets only reflect\nplanets move through an orbit (around stars), stars don't
1046084
TVs use cathode ray tubes to provide the picture, they need time to "warm up" before you can see the picture.  The speakers that relay the sound though are basically instantaneous.
54981
i believe it's the magnification (or other distortion such as increased brightness) of the appearance of a star in the sky or through a telescope. the diffraction can be eliminated digitally, but other than that i'm not sure.
468156
Most--not all--shooting stars (meteors) are about the size of a grain of sand. Most of these specks are left-over material from comets that have passed in and out of the inner solar system.\n\nGod should be spelled B-I-G B-A-N-G\nPBrax@netscape.com
50872
This was one of the claims made in a effort to debunk the moon landings. Here is an explanation on why no stars are seen in pictures taken in space.\n\n"The black sky should be full of stars, yet none are visible in any of the Apollo photographs. \n\nThis claim is one I hear frequently, and is one of the easiest to refute. The answer is very simple: they are too faint. The Apollo photos are of brightly lit objects on the surface of the Moon, for which fast exposure settings were required. The fast exposures simply did not allow enough starlight into the camera to record an image on the film. For the same reason, images of the Earth taken from orbit also lack stars. The stars are there; they just don't appear in the pictures. The hoax advocates often argue that stars should be visible, and some of their claims are valid, however they fail to recognize the difference between "seeing" stars and "photographing" stars. The astronauts could have recorded star images in their photos by increasing exposures, but they were not there to take star pictures. The purpose of the photos was to record the astronauts' activities on the surface of the Moon. \n\nBill Kaysing claims that NASA has perpetrated the lie that stars cannot be seen in space to validate the lack of stars in the Apollo photos. This assertion is utterly ridiculous; in fact, NASA has released many photos in which stars are visible. Common among these are long-exposure nighttime photographs of aurora taken by space shuttle astronauts. This example [see photo] is a four-second exposure taken from the flight deck of the shuttle Endeavour"
216038
http://www.ufos-aliens.pwp.blueyonder.co.uk/Apollo1.rm \n\nNow you decide:) And why are the stars absent? The Lunar camera crosshairs:\n-If you examine the Lunar Landing pictures carefully, you will notice that the lenses were fitted with crosshairs. Examine them even closer, and you will find that several items, such as the American Flag and the Lunar Lander, are actually over the crosshairs. How can this be?  But since I was not there on the moon myself then I would never say I am 100% sure it did not happen.
1091585
You've awakened the starry-eyed dreamer in me at this late hour!  I should be sleeping, but can't resist your question.\n\nHow many other planets, do I think?  Actually my number is a lot higher than millions!  In fact, on this subject you get into numbers so large that most of us humans cannot relate them to anything in our experience.  So, sadly, I doubt we can appreciate the grandeur of the universe.  But let me try...\n\nOne fairly recent estimate says there are 70 sextillion *visible stars* in range of modern telescopes (70,000 million million million).\n\nTo help put that in perspective, I'll use a rather old but useful analogy.  Imagine scooping up a big handful of sand at the beach. Try counting the grains of sand.  You'll give up, most likely, in seconds, assuming you even bother to try.  Now look all around you on the beach, and think about *that* number.  Now think about all the grains of sand on *all the world's* beaches... and deserts.  Now multiply that total number by ten, and you get approximately the number above -- of stars in the *known* universe.  The stars not visible to us by even our most powerful telescopes may equal the visible figure -- or be multiples of it.  Mind-boggling, no?\n\nSo to your planet question:  One next has to wonder how many of those stars are actually a sun to one or more planets (hey, I just noticed that was your wording, too; I like it).  Does every star have at least one planet revolving about it?  \n\nWell let's just be very conservative and say that there are only 70 sextillion stars in the *entire* (not just known) universe.  Let's further say that only one tenth of those stars (7 sextillion) have a planet orbiting them.  If we assume merely one planet per sun, then there must be at least 7 sextillion planets in the universe.  Using our sand analogy, that's a planet per grain of sand on all the world's beaches and deserts!\n\nAnyone who believes that is a reasonable number must surely wonder, "How could there NOT be living beings somewhere other than the earth?"  \n\nOf course not all planets will have life on them.  Earth may be the only body in our solar system, for example, which does harbor life, though at least one of Jupiter's moons is also a tantalizing possibility.\n\nIf only one out of a *thousand* of those planets are earth-like -- in the sense that they are rocky, not gaseous, and contain liquid water -- there may be 7 quintillion earth-like planets in the universe.  That's 7,000 thousand trillion.  I've been very careful, but if my math or estimates are off by even a factor of a *billion* there could be 7,000 million earth-like planets in the universe, a figure I think is extremely low.\n\nThese figures seems to jibe fairly well with an estimate of the number of earth-like planets in our galaxy alone, found at space.com (the bottom link in my sources) -- 30 billion, from a 2002 article.\n\nMy personal belief, based on numbers such as this, and on the likelihood that any planet supporting life may contain (extremely conservatively!) a thousand species...  is that there are *billions* of intelligent species in the universe outside the earth.\n\nSince you were wise to point out that we reside in the Milky Way galaxy, which is only one of perhaps billions of galaxies, you might be fascinated by the Hubble photo in the references, below.  I liked it so much, myself, that I made it my new desktop wallpaper.\n\nFinally, on the specific subject of life, there is a well-known method of estimating the number of intelligent, communicating civilizations, called the Drake Equation.  In my references you can see how it works to condense all the possible stars down by multiple factors, leaving the fraction which we may be able to communicate with, or at least hear from!  \n\nHappy dreaming (for me, too), and I hope you are as inspired by all this as I am.   :-)
184581
there are places where there are no stars, just because they can be so far apart, and there are also stars that are so far away, or not very bright that can't be seen from earth, then of course there's all that light pollution that blocks many stars from being seen - go to a city ur lucky if u see one, but out in the country........ its beautiful
193159
A star is basically a giant hydrogen bomb. It sits in space for billions of years fusing hydrogen into helium, creating loads of light and heat, among other things.\n\nA planet orbits a star, and is just a piece of matter that does not perform nuclear fusion. Some of them are rocky balls (like the Earth, or Mars), while some of them are giant balls of gas (like Jupiter, or Saturn).\n\nEDIT: fungusbrains1, planets twinkle too. They don't produce their own light, but they reflect light from the Sun. Any cosmic object whose light rays pass through the atmosphere twinkles.
331809
science_FREAK, you think the furthest star is just 82 million km away????!!!  That wouldn't even take us out of our own solar system!  In fact, our star, the Sun, is 150 million km away!\n\nIf you mean why do some stars "appear" brighter than others, then that is because stars are at different distances from the Earth, and they are different sizes.  IF you had 2 identical stars, but one was twice the distance from the Earth that the other, then the further away one would appear much dimmer in the sky.\n\nBut all stars shine with a slightly different brightness, I doubt that any two are identical.  So the appearance of some stars being brighter than others is down to size of stars and how far away from us that they are.