A Week After the Full Moon the Moon Looks Like a Semicircle Again
The Moon, like every other planet and satellite in the solar system, shines not with its ain lite but with the reflected light of the Sunday. This means that at any signal in time one half of the Moon is lit while the other half is in darkness. As the Moon revolves around the World, over a period of about 29 days, a varying proportion of the illuminated half tin can be seen from the Earth. The purlieus betwixt the lite and dark halves, chosen the terminator, migrates from east to due west beyond the lunar surface and, considering the Moon is spherical, creates the familiar phases: crescent, full, etc.
The Moon rises and sets in roughly the same directions every bit the Dominicus, but about 49 minutes subsequently each night than the dark before. The cycle of phases, chosen a lunation or synodic month, begins with a new moon, when the Moon passes close to the Sun and so cannot exist seen confronting its overwhelming glare. This is the time when solar eclipses can occur, but for reasons described in some other commodity they usually do not.
A couple of evenings later the Moon has moved abroad from the Sunday. It sets a footling later dusk, and then tin exist briefly observed as a thin crescent low in the west. The phase of the Moon facing the Earth is ever the exact opposite of the stage of the Earth facing the Moon, and then although very little of the sunlit portion of the Moon is visible from the Earth there is quite a lot of earthshine on the night portion. Sometimes this is enough to faintly reveal the Moon'south whole disc, a phenomenon known as "the sometime moon in the new moon's arms".
Over successive nights it becomes easier to detect as it sets progressively later and as its phase becomes larger (called waxing). Nigh a week after the new moon the phase has reached a semicircle. Despite the shape, this a called the showtime quarter, because information technology marks one quarter of a lunation. This is the phase most oftentimes seen during the daytime, as it rises effectually noon, sets at about midnight, and is highest effectually 6pm. In fact, over a month, the Moon is in the sky for equally many hours during the day as during the night. However information technology is merely at this time, when it begins to spend more than one-half of its time equally a nighttime object, that information technology has become sufficiently well illuminated to evidence upwardly in the bright daytime skies.
Equally the waxing continues, the next stage is chosen gibbous - a disc with just a crescent missing from it. Then, some 14 days after the new moon, we see a full moon - the Dominicus and the Moon are on contrary sides of the Globe, and when ane sets the other rises. This is the period when lunar eclipses tin happen, merely for the aforementioned reasons as for solar eclipses they remain unusual.
From this indicate onwards for the remainder of the lunation the Moon's phase becomes thinner again, called waning. It passes through gibbous phase, then roughly three weeks after new, it becomes a one-half circumvolve again, the mirror of the kickoff quarter, called (for obvious reasons) the last quarter. Again this is a phase often seen in the daytime, only during the morning equally information technology rises at well-nigh midnight and sets around noon.
The last phase is a crescent once more, ending with another chance to see the effect of earthshine (this fourth dimension called "the new moon in the old moon'south arms"). Then, virtually 29 days after the last new moon, another takes place, with the Sun and Moon rise and setting at much the same times, and the whole process repeats.
Source: http://www.inconstantmoon.com/cyc_phas.htm
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