Why is there a circle around the moon?
397227
From http://home.hiwaay.net/~krcool/Astro/moon/moonring/\n\nThe ring around the Moon is caused by the refraction of Moonlight (which of course is reflected sunlight) from ice crystals in the upper atmosphere. The shape of the ice crystals results in a focusing of the light into a ring. Since the ice crystals typically have the same shape, namely a hexagonal shape, the Moon ring is almost always the same size.
287587
The phases of the moon are caused by the relative positions of the earth, sun, and moon. The moon goes around the earth, on average, in 27 days 7 hours 43 minutes. \n\nThe sun always illuminates the half of the moon facing the sun (except during lunar eclipses, when the moon passes thru the earth's shadow). When the sun and moon are on opposite sides of the earth, the moon appears "full" to us, a bright, round disk. When the moon is between the earth and the sun, it appears dark, a "new" moon. In between, the moon's illuminated surface appears to grow (wax) to full, then decreases (wanes) to the next new moon. \n\nThe edge of the shadow (the terminator) is always curved, being an oblique view of a circle, giving the moon its familiar crescent shape. Because the "horns" of the moon at the ends of the crescent are always facing away from the setting or rising sun, they always point upward in the sky. It is fun to watch for paintings and pictures which show an "impossible moon" with the horns pointed downwards.
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.
333816
moon moves in clockwise direction
552110
The moon appears at different angles because like any given solid object, everyone is looking at it from different positions, just like three people looking at a car.\n\nPlace a ball in a dark room, place a torch on a piece of furniture across the room from it. Now place another ball somewhere mid distance, switch the torch on, and walk around the room. Notice how the shadows shape on the furthest ball alters.\n\nNow you have to remember that we are on that ball nearest the torch, and we are walking around the curve. The shape and the angle will change even more just depending on where you are on that ball.
1038717
Refraction of the light through the atmosphere, and the fact that the moon's orbit is not circular, but elliptical, so there are times when it is a bit closer than others.
830404
The moon is often visible during the daytime! If it's not visible during the daytime where you are, it's visible from somewhere else on Earth.
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 . . ."
968800
It is the shadow of the Earth or rather, the part you see is the part that is not in the shadow of the Earth.\n\nThe shape the moon appears depends on its position relative to the Earth and the Sun. Depending on the timing, the shadow the Earth casts on the moon will change.\n\nSince the orbits of the moon and earth are constant, astronomers thousands of years ago have been able to predict the shape of the moon depending on the date.
261004
Although the Moon does not appear to have a magnetosphere surrounding it, it *is* a magnetic object in space. Scientists think that the magnetism of the Moon's surface is leftover from a time when the Moon's magnetic field was actively created by a dynamo within the lunar core, and that this remnant magnetism may gradually erode away. \n\nTheories also suggest that the Moon's magnetism may come from collisions with other celestial bodies such as asteroids and comets, which might have imparted to the Moon some magnetic properties. \n\nSome regions of the Moon's surface are more magnetic than others. A strip of the lunar crust called the Rima Sirsalis seems to be very strongly magnetic. Measurements of the uneveness of the magnetism and depth of the lunar crust such as those being made by the Lunar Prospector mission can supply information about the magnetism of the surface, as well as the size and electrical conductivity of the lunar core. Ultimately these measurements will help scientists better understand the Moon's origins. For example, if the core contains more magnetic elements (such as iron) than the Earth, then the collision/ejection theory of lunar origin loses some support. \n\nScientists believe that certain lunar surface features, such as the albedo swirls, may have magnetic origins. The swirls resemble unstirred cream in a coffee cup. Researchers suspect that the contrasting light and dark regions might indicate the juxtaposition of irregular magnetic fields. Using data obtained both from its Magnetometer and Electron Reflectometer instruments, Lunar Prospector will map global locations, strengths and orientations of lunar crustal magnetic fields. With these experiments, scientists can learn if there is a relationship between such magnetic fields and the surface.
225731
Here is a very simple and precise explanation with good illustrations\nhttp://home.hiwaay.net/~krcool/Astro/moon/moonorange/
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.
1087183
The moon has a side that always faces us! That's not always filled with light though. That's why we have phases of the moon.
439041
The Moon is 400 times smaller than the Sun AND 400 times closer. Why? I don't think there is any real reason, we are just lucky.
688214
The flag placed on the moon (or any other man made object on the moon) is far too small and way too far away to be seen by any telescope on (or orbitting above) Earth, the angular size is just too small.\n\nIt can be verified mathmatically that it is impossible to see the flag with a telescope from Earth using the formula to find the minimum angular resolution size as seen through a circular aperture,\ntheta_min = 1.22 * lambda / Diameter\nwhere theta_min is the minimum angle (in radians), lambda is the wavelength of light, and Diameter is the diamter of rhe circular opening you are viewing it through.
7285
THe bright ring is called a 'halo'\n\nIt's a fairly common sight and occurs when high thin clouds containing millions of tiny ice crystals cover much of the sky. Each ice crystal acts like a miniature lens. Because most of the crystals have a similar elongated hexagonal shape, light entering one crystal face and exiting through the opposing face refracts 22 degrees, which corresponds to the radius of the Moon Halo. \n\nSee a nice picture here:\nhttp://antwrp.gsfc.nasa.gov/apod/ap000515.html
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.