why is the moon only half but then on other days it is full moon or quater moon?
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.
835797
The next time there's two full moons in the same month
812275
The Moon rotates on it's axis and revolves around the Earth in 27 1/3 days. The time from one full moon to the next is 29 1/2 days. The reason they are not the same is that during the 27 1/3 days that it take the Moon to go around the Earth, the Earth has moved relative to the Sun, and it takes another 2 days or so before the Moon is directly on the other side of the Sun (which is what gives a full moon). It is similar to the reason why the Earth rotates on its axis once every 23 hours 56 minutes and 4.1 seconds, but its 24 hours from noon to noon.
405607
The phases of the moon occur due to its relative position to us and the sun. The sun always shines on half of the moon (except on the rare occassion when the earth is in the way causing a lunar eclipse). If the moon is behind the earth, we see it as a full moon as we can see all of the lit side. When the moon is beside the earth, we see half the lit side and half the side in shadow, which appears to us as a half moon. When it's in front of the earth its a new moon which isn't visible as we can only see the side of the moon in shadow. In between the stages we see the crescent waxing and waning moons.
61467
The moon spins about an axis. The axis  is almost perpendicular to the plane of the moons orbit around the earth. The period of spin (time to complete one rotation about the spin axis) is equal to the period of one revolution around the earth.\n  The result is we see one side of the moon.\nFor many people this answer is not suffice to understand.\nImagine a cubical building in a plain ground. The four vertical walls are marked A,B,C,D.  Imagine the building to be the moon and we are standing infront of the wall marked A. Let us go round the building to see the other walls in the order of ABCD. When we have finished quarter round we can have the full view of the wall B. But imagine  that the building rotates itself such that when we finished quarter round it also has rotated quarter round about itself. We will see only the wall A. If the things continue like this we can never see the other walls.When we complete one round the building completes one round so always we see only the wall A.\n Due to librations actually we can see 59% of the moon instead of 50%
77452
New Moon - The Moon's unilluminated side is facing the Earth. The Moon is not visible (except during a solar eclipse).\nWaxing Crescent - The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing.\nFirst Quarter - One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing.\nWaxing Gibbous - The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing.\nFull Moon - The Moon's illuminated side is facing the Earth. The Moon appears to be completely illuminated by direct sunlight.\nWaning Gibbous - The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing.\nLast Quarter - One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing.\nWaning Crescent - The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing.\nalso go to \nhttp://tm.ask.com/r?t=an&s=a&uid=09220EDD36C718A34&sid=144454D585BB38B34&o=0&qid=0F1134A30408E249734C01A371E2BB7D&io=0&sv=0a300524&ask=moon+phases&uip=480e4587&en=te&eo=1&pt=Moon%20Phases&ac=6&qs=1&pg=1&u=http%3A%2F%2Faa.usno.navy.mil%2Ffaq%2Fdocs%2Fmoon_phases.html
236149
The moon spins about an axis. The axis is almost perpendicular to the plane of the moons orbit around the earth. The period of spin (time to complete one rotation about the spin axis) is equal to the period of one revolution around the earth.\n\nThe result is we see one side of the moon.\n\nFor many people this answer is not suffice to understand.\nImagine a cubical building in a plain ground. The four vertical walls are marked A,B,C,D. Imagine the building to be the moon and we are standing infront of the wall marked A. Let us go round the building to see the other walls in the order of ABCD. When we have finished quarter round we can have the full view of the wall B. But imagine that the building rotates itself such that when we finished quarter round it also has rotated quarter round about itself. We will see only the wall A. If the things continue like this we can never see the other walls.When we complete one round the building completes one round so always we see only the wall A.\nDue to librations actually we can see 59% of the moon instead of 50%
153461
If the sun and the moon are both visible at the same time, then the first answer of course would be daytime.  However, for the moon to be visible during the day, it has to have risen somewhere in the 6 am - 6pm range.  this means that the moon can be in any phase from new moon through first quarter and almost to full moon.  So, the final answer to the question would be that when the sun and moon are both visible, it is called daytime during the first half of the lunar cycle.
174140
the lunar cycle is just about 28 days, not exactly though. Allowing for it to be 28. divide 365 by 28 and you have 13.  So depending on what phase of the moon you have at the start of the year, you will have 13 of them that year. Consequently each year will start with a different phase so you will have 13 different ones each year. Allow for the fact that the lunar month is not exactly 28 days even adds to the situation. On occasion you will have two full moons in one calender month, a "Blue Moon".  Each full moon has a name for it based on folk lore and legends. Harvest moon, the full moon closest to autumn to allow light for harvesting later....etc. A tidbit of info....the moveable holiday of Easter can always be determined as the first Sunday, after the first Full Moon after the beginning of Spring.
758225
I can only assume you need to know how long the moon cycle is and where the half moon falls in the moon cycle.\n\nA moon cycle is 28 days long, so a half moon occurs on the 14th day of the moon cycle, oposite the "New" moon.\n\nHope this helps!
11819
The harvest moon is the full moon that occurs closest to the fall equinox (usually late September or early October).  It got its name because the full moon was so bright that farmers could continue working on their crops late into the night.
1142453
Well it's a natural phenomenon. If moon is not rotating then some thing else any where else in our solar system will do something to compensate for this energy.\n\nRemember : Energy can neither be created nor be destoyed and according to the energy conservation principle this energy will have to be redirected . So it can be millions of other possibilities :)\n\nLike days will be shorter ans earth rotates fast to use that excess energy or something like that.\n\n:)
781232
This phenomenon happens rarely and is where the phrase "once in a blue moon" comes from. It will occur in months with 31 days if the first full moon of the month occurs on the first day of the month. The moon cycles through the phases on a 28 to 29 day cycle, so a second full moon or "blue moon" would occur during the last week of the same month. Don't hold your breath waiting for this to happen-you could turn "blue".
663878
A full moon is the phase when the entire circular shape of the moon is visible.\n\nA new moon is the phase when no part of the moon is visible due to the position of the earth.  It happens to block the light from the sun so the moon is not able to be seen.\n\nsilly fact- the term "blue moon" like "once in a blue moon" refers to the unusual event of having two new moons in a calendar month.
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"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.
359151
No.  The angle between the sun and the moon as viewed from the earth is 180 degrees for the full moon pahse.  This means that the full moon and the sun are always on opposite sides of the earth.\n\nSince the moon is not always "in plane" with the sun, and your horizon is not perfect, it may be possible on occasion, depending on the geography of the horizon, and one's latitute to see the full moon rising as the sun is setting, or to see the full moon setting as the sun is rising.
200197
Although the full moon occurring Saturday, June 30, 2007, will look like an ordinary full moon, it will actually be a bit extraordinary—a blue moon.\n\nWhat is a Blue Moon?\nThere are in fact two definitions for a blue moon. According to the more recent definition, a blue moon is the second full moon in a calendar month. For a blue moon to occur, the first of the full moons must appear at or near the beginning of the month so that the second will fall within the same month (the average span between two moons is 29.5 days). June 2007 will have two full moons: the first on June 1, the second on June 30—that second full moon is called the blue moon.\n\nThe Other Kind of Blue Moon\nAn older definition for the blue moon is recorded in early issues of the Maine Farmer's Almanac. According to this definition, the blue moon is the third full moon in a season that has four full moons. Why would one want to identify the third full moon in a season of four full moons? The answer is complex, and has to do with the Christian ecclesiastical calendar. \n\nSome years have an extra full moon—thirteen instead of twelve. Since the identity of the moons was important in the ecclesiastical calendar (the Paschal Moon, for example, used to be crucial for determining the date of Easter), a year with a thirteenth moon skewed the calendar, since there were names for only twelve moons. By identifying the extra, thirteenth moon as a blue moon, the ecclesiastical calendar was able to stay on track. \n\nFor a fuller explanation see http://www.inconstantmoon.com/cyc_blue.htm. For more background information on the controversy over the two definitions of blue moon, see the Sky and Telescope article, "What's a Blue Moon?" In it they explain how the two different definitions of a blue moon came about—including their own role in introducing the second, modern definition. \n\nA Star Rating for the Modern Blue Moon \nAlthough Sky & Telescope calls the modern blue moon definitition "trendy" and a "mistake," the fact that there is an older, preexisting (and more complicated) definition does not necessarily make it the more interesting or meaningful definition. Charting the "third full moon in four full moons" in a season isn't everyone's idea of an fascinating enterprise. The modern, "trendy" definition, however, points to an intriguing astronomical phenomenon—every so often two moons can manage to position themselves in the same month. Given that full moons occur once every 29.5 days, this is quite an accomplishment!\n\nHow Often Does a Blue Moon Occur?\nOver the next twenty years there will be a total of 17 blue moons, with an almost equal number of both types of blue moons occurring. No blue moon of any kind will occur in the years 2006, 2011, 2014, and 2017.\n\nThe more recent phenomenon, where the blue moon is considered to be the second full moon in a calendar month, last occurred on July 31, 2004. Two full moons in one month may occur in any month out of the year except for February, which is shorter than the lunar cycle.\n\nThe other, older blue moon event, which happens when there are four full moons in a season, last occured in August 2005. Since this type of blue moon is reckoned according to the seasons, it can only occur in February, May, August, or November, about a month before the equinox or the solstice.\n\nTwice in a Blue Moon\nThe rare phenomenon of two blue moons (using the more recent definitition) occurring in the same year happens approximately once every 19 years. 1999 was the last time a blue moon appeared twice, in January and March.\n\nThe months of the double blue moons are almost always January and March. That is because the short month that falls in between them, February, is a key ingredient in this once-every-nineteen-year phenomenon. For January and March to each have two full moons, it's necessary for February to have none at all. Since February is usua