Why does the moon always show the same face to earth during the day? And why does it cover the sun exactly dur
370080
Finally a good question.\n\nThe Moon's apparent size being very similar to the Sun's apparent size is a coincidence. But the Moon doesn't always cover the Sun during an eclipse, look up annular eclipse (the looks smaller), and when it does cover it, it is usually a bit larger.\n\nBut now let's talk about the main question.\n\nWe always see the same side of the Moon because its during its full rotation around the Earth it also makes a full rotation around its axis. This is not a coincidence. There are several satellites in the solar system whose rotation is synchronized with their rotation around a planet (eg. Io around Jupiter, Charon around Pluto but also Pluto around Charon :-) etc. ).\n\nThe Earth's gravitation decreases with the distance from its center. So the Moon's opposite side (which is further away from the Earth) is attracted less by the Earth than the side which is closer. This results in the Moon being a little bit deformed along the Earth-Moon line.\nThe Moon is a little bit shaped like an egg: if it would rotate faster, it would not be elongated towards the Earth anymore, and the Earth's gravitation would try to turn it back. This is very difficult to explain without the opportunity to draw figures ... but anyway, search for tidal locking on the net, I hope you'll find a good, illustrated explanation.\n\n\nEDIT: In one answer someone said that Mercury is in a similar relation with the Sun ... this is not exactly true, as the ratio of period of its rotation and the period of its orbiting is 3/2.\n\nMercury also has an elongated shape: due to this 3:2 resonance, at its perihelion, the axis of its elongation is always parallel with the Sun--Mercury axis.\n\nEDIT2: As I said, the apparent size of the Moon is just a concidence. Other planents do get total eclipses. What does a total eclipse mean? It means that a moon casts a shadow on the planet: http://www.c-science.com/txt/images/1999/990428unssx2.jpg\n\nThere is a nice program calles Celestia, which can show you the eclipses caused by various moons on various planets (3D animations): http://www.shatters.net/celestia/
147029
The moon gets in the way of our view of the sun.  Since coincidentally, the two disks (i.e., two-dimensional view of a sphere) have the same apparent size when viewed from the earth, the moon covers most of the sun, exposing the corona, which is normally invisible.  The corona is the thinner part of the sun which is not normally visible because of the glare from the main disc.\n\nHowever, here's an interesting question:  how far out in space would you have to be before looking at our sun (call him Sol), you would just see a bright star, and part of that star would be the earth?  That is, when we say "the solar system" to include ourselves and everything out to Pluto, an observer from far out in space would just say "Sol," and mean to include us.  Jefferson Starship sang, "We rode a bubble through the sun . . ."
32936
"The moon does not circle the Earth once a day. The Earth circles the sun once a day. The Moon orbits the Earth about twice every 24 hours. That's why we have tides (high and low)."\n\nSAY WHAT?  Not even close.  There are junior high science teachers weeping over this "answer".\n\nThe earth rotates once a day on its axis.  That is the definition of a day - the time it takes for a planetary body to rotate once on its axis. \nThe earth circles the sun once a year - actually 365.24 days (which is why we have leap years).  That is the definition of a year - the time it takes for a planet to orbit the sun.  As you can tell, planetary years are longer or shorter depending on the distance from the sun.\nOur earth's axis is tilted.  The northern hemisphere is closer to the sun in the summer and farther in the winter.  This is how we get seasons.\n\nThe moon orbits the earth once every twenty-eight days, give or take an afternoon. The phases of the moon are caused by it being in a slightly different position everyday relative to the sun.  \nThe moon does cause tides - its gravitational pull causes the oceans to bulge out towards the moon.  However, there is a matching bulge directly opposite the moon.  THAT is why we have two high tides and two low tides a day.  In addition, the sun exerts a lesser pull, which interacts with the moons pull.\n\nSorry about that - had to correct the flagrant misinformation there.\n\nAs for your question - it is a weird effect, isn't it?  Especially when the moon is closer to a new moon.\n\nWhat happens is that our atmosphere scatters the light from the sun so that our sky is quite bright.(Why is the sky blue? has been discussed here many times).  However, the moon is reflecting enough light so that it is brighter than the surrounding sky and we see it.\n\nWhen the moon is less than full, there is very little light reflected off of the dark side of the moon (what light is reflected is earthshine!)  This light is not bright enough to outshine the sky.\n\nThink of a white sheet (in a dark room) that images are being projected onto.  The sheet will look opaque until someone shines a light onto it from the back that is brighter than the image projected from the front.  That is the basic effect that we are getting - the atmosphere is a sheet, with the sun and the moon both shining on to it.
20309
I want to add more:\n1) Due to the distance to the Moon relative to the size of our planet, it doesn't really matter from which point on Earth you are looking at our natural satellite. You will see virtually the same part of the surface.\n2) The reason the Moon rotates around its axis at about the same time it rotates around the Earth is because it is tidally locked with the Earth. Tidal lock worked for billions of years to achieve the present effect, but it's still not perfect: the Moon slightly advances or gets behind in its axial rotation relative to its revolution around the Earth. So, over time, we are actually able to see around 57% of its surface, rather than just 50%.\n3) The Earth is not close enought to the Sun to be tidally locked by its gravity (even Mercury, the closest planet to the Sun, isn't). So that's why the Sun-Earth relation is different.
407247
Curious is correct. It is tidal lock, not coincidence, that causes the phenomenon you ask about. Eventually, the earth would get into tidal lock also, and always show the same face to the moon, but before that happens the sun will expand in its death throes and engulf the planetary orbits out beyond Mars.
115838
The moon is very far away from the Earth.  It may be hard to imagine, but it is possible to see the moon from many different points on the earth at the same time.\n\nAlso realize that all of Earth experiences the same phase of the moon at the same time.  When we see a full moon, the people on the other side of the world are seeing the same full moon.
477677
Cautious cook is a moron!  The moon, as anyone knows who passed high school physical science, remains the same distance while orbiting around the earth (us).  Also, interesting to note, the rotation of the moon is, in relation to the orbit, the same speed.  Meaning no matter at what part of the orbit, the moon is, we always see, the same side of the moon.  This is known as the light side of the moon.  The only way to see the dark side is to go there.  Apollo did this.  Now, onto your question it is very easily answered.  Just as a lens warps light to make things appear closer or farther away, the atmosphere of the earth is curved causing the same effect towards the horizon.  The reason you don't have this effect when the moon is overhead is because you are looking through less of the atmosphere, and the effect is less prominent.
869305
The appearance of the Moon is also dependent on the fact the the Earth is rotating on its axis. Objects appear at the horizon, drift overhead and slip below the horizon again. that is the main reason the Moon looks as it does.\n\n;-D The Moon is romantic! Let's not forget that!
1116527
The Moon rotates at just the right speed so that it always keeps one face pointed toward the Earth. Almost all moons in the Solar System keep one face pointed toward their planet. \n\nThe moon rises in the east, and sets in the west. It moves from east to west, right? If you think about it, you should realize that much of the moon's apparent motion is due to the spin of the earth. The moon appears to go around the earth about once a day. And, you probably know that the moon actually takes about a month to go around the earth. That's where we get the word "month."\n\nWhy don't you perform a simple observation. Look at the moon, some night, and see where it is with respect to the stars (or with respect to the sun). You don't need to know the stars very well, but you probably want to ignore the planets (Venus, Jupiter, and Mars, mainly, as their motion complicates this observation). Night after night, the moon moves against the background of stars. See if you can tell which way the moon is moving, against the background of stars.\n\nAnother simple observation would be to keep track of when the moon rises (roughly) or sets from night to night. Does it rise later each night, or earlier, or what?\n\nYou will see that the moon moves west to east, fairly rapidly. \nWhich way does the earth spin? Well, the stars, sun, moon, and planets all seem to be moving east to west. So the earth is spinning in the opposite direction, west to east. Hey, the moon is also moving west to east, coincidence? Well, the earth is moving around the sun from west to east. In fact all nine of the planets are moving around the sun from west to east. And, all of the planets, except Uranus (which is lying on its side) and Venus (which is spinning slowly backward), are rotating from west to east. And most of the moons, of the various planets, are orbiting their planets from west to east. And most of the asteroids are orbiting the sun from west to east.\n\nIt's not a coincidence. The Solar System started out as a cloud of dust and gas, and it was rotating from west to east. That's why most of its parts are still rotating and orbiting from west to east.
11081
A full moon is simply fully visible.  Usually, the earth is between the sun and the moon to some degree.  The curved shadow on the moon is the shadow of the earth.  A full moon is when the moon is slightly to the side of the earth and the sun is shinging on the entire surface with no shadow of the earth on it.\n\nSee the link below for a good explanation.
733762
It reflects the light of the sun.  What on the moon could possibly produce light?  There's no fire, nuclear reactions, or anything of the like going on there.  Want to prove it yourself?  Go outside on a day where you can see both the moon and the sun in the sky.  Take a good look at the phase of the moon.  Which side of the moon is lit up?  The side facing the sun, since the moon is reflecting the sun's light.
1166386
The shape of the moon does not actually change, but it is the shadow of the earth that gives the illusion. The moon revolves around the earth due to which we have full moon, no moon and half moon periods as it travels betweeen the shadow of the earth. During the period from no moon to full moon, the earth is in between the moon and the sun due to which the earth's shadow falls directly on the moon and thus we cannot see the illuminated part of the moon.As the earth graduallly moves away from the position, we can see the illuminated part of the moon which appears in the shape of a crest.  Also due to the non existence of atmosphere on the moon, there is distinct difference in the illuminated and the dark part of the moon. During the period from full moon to no moon, it again moves from the shadow of the earth and thus at one point is completely overshadowed by the earth and doing the disappearing act.
329109
The reason you can see the moon in the sky during the day is because at that time the moon has rotated to where it is inbetween the earth and the sun.  So they are both visable at the same time.  It takes 28 for the moon to circle the earth, this is also the cause of moon phases, such as full moon/ new moon ect.
47510
The moon DOES rotate.  The reason you cannot detect it is because it is in a synchronous rotation, meaning that it takes the same ammount of time to revolve as it does to rotate, meaning that the same face (the Light side) is always facing us.  It may be hard to visualize at first, but imagine you are the moon.  Now, stand facing an object, like a pole which will be the Earth.  Now, practice spinning around (revolving) so that you can do it in exactly 10 seconds.  Now, practice walking around the pole so that you are rotating for exactly 10 seconds.  Now, do them both together.  From your perspective (as the moon) you ARE rotating, but you'll notice that your face (the Light side of the moon) is always facing the Earth.
1027317
You mean the moon and the sun, which is true\nsometimes, but there are also eclipses where\nthe moon is smaller than the sun, so a small\nring of light is left uncovered (called an annular\neclipse)...\n\nBy a stroke of amazing coincidence, both the\nmoon and the sun are approx 108 times as\nfar from the earth as their diameter, so they\nappear the same size in the sky... 108 is a\nmystic number in spirituality, so I doubt if this\nis really a coincidence!
933431
The Moon is spherical, so of course half of it's hidden all the time. The Moon's in a tidally locked orbit as well, so the same face is always towards Earth; 44 percent of the Moon's surface can never be seen from Earth.\n\nBut I don't think that's what you were asking. I think you were asking why the Moon looks like a sliver. It's also simple: the Moon is lit by sunlight. You will notice the bright part of the Moon ALWAYS, without exception, points at the Sun. (Sometimes you can faintly see the side away from the Sun; this faint illumination is sunlight bouncing off Earth's clouds and feebly illuminating the Moon through radiosity.)\n\nTo demonstrate the phases of the moon, get a ball and a lamp in a darkened room. Hold up the ball in front of you and turn around. Notice the phases of the ball, just like the Moon.
439809
The moon is basically a great big lump of dull coloured rock that floats around quarter of a million miles from us.  Just like earth, it's illuminated by the sun so what you're seeing is reflected sunlight.\n\nIt can appear as different colours due to the atmosphere here on earth.\n\nWhen the moon is up in the sky you're looking at it through a thin layer of atmosphere but when it's low on the horizon you're looking through a greater amount of atmosphere.\n\nThe way that our atmosphere breaks up sunlight into differnt colours (Rayleigh Scattering) affects the colour that the moon appears to be.  So too can particles in the atmosphere - particularly dust and volcanic ash which often gives it a reddish tinge.