why are there moon phases?

Answer 1

From any location on the Earth, the Moon appears to be a circular disk which, at any specific time, is illuminated to some degree by direct sunlight. Like the Earth, the Moon is a sphere which is always half illuminated by the Sun, but as the Moon orbits the Earth we get to see more or less of the illuminated half. During each lunar orbit (a lunar month), we see the Moon's appearance change from not visibly illuminated through partially illuminated to fully illuminated, then back through partially illuminated to not illuminated again. Although this cycle is a continuous process, there are eight distinct, traditionally recognized stages, called phases. The phases designate both the degree to which the Moon is illuminated and the geometric appearance of the illuminated part. These phases of the Moon, in the sequence of their occurrence (starting from New Moon), are listed below.

New Moon - The Moon's unilluminated side is facing the Earth. The Moon is not visible (except during a solar eclipse).
Waxing 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.
First 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.
Waxing 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.
Full Moon - The Moon's illuminated side is facing the Earth. The Moon appears to be completely illuminated by direct sunlight.
Waning 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.
Last 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.
Waning 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.

Following waning crescent is New Moon, beginning a repetition of the complete phase cycle of 29.5 days average duration. The time in days counted from the time of New Moon is called the Moon's "age". Each complete cycle of phases is called a "lunation".

Because the cycle of the phases is shorter than most calendar months, the phase of the Moon at the very beginning of the month usually repeats at the very end of the month. When there are two Full Moons in a month (which occurs, on average, every 2.7 years), the second one is called a "Blue Moon". See the article "Once in a Blue Moon" for the story of how the usage of this term has evolved

The first time that the thin waxing crescent Moon is visible after New Moon (low in the evening sky just after sunset) marks the beginning of a month in the Islamic Calendar.

Although Full Moon occurs each month at a specific date and time, the Moon's disk may appear to be full for several nights in a row if it is clear. This is because the percentage of the Moon's disk that appears illuminated changes very slowly around the time of Full Moon (also around New Moon, but the Moon is not visible at all then). The Moon may appear 100% illuminated only on the night closest to the time of exact Full Moon, but on the night before and night after will appear 97-99% illuminated; most people would not notice the difference. Even two days from Full Moon the Moon's disk is 93-97% illuminated.

New Moon, First Quarter, Full Moon, and Last Quarter phases are considered to be primary phases and their dates and times are published in almanacs and on calendars. The two crescent and two gibbous phases are intermediate phases, each of which lasts for about a week between the primary phases, during which time the exact fraction of the Moon's disk that is illuminated gradually changes.

The phases of the Moon are related to (actually, caused by) the relative positions of the Moon and Sun in the sky. For example, New Moon occurs when the Sun and Moon are quite close together in the sky. Full Moon occurs when the Sun and Moon are at nearly opposite positions in the sky - which is why a Full Moon rises about the time of sunset, and sets about the time of sunrise, for most places on Earth. First and Last Quarters occur when the Sun and Moon are about 90 degrees apart in the sky. In fact, the two "half Moon" phases are called First Quarter and Last Quarter because they occur when the Moon is, respectively, one- and three-quarters of the way around the sky (i.e., along its orbit) from New Moon.

The relationship of the Moon's phase to its angular distance in the sky from the Sun allows us to establish very exact definitions of when the primary phases occur, independent of how they appear. Technically, the phases New Moon, First Quarter, Full Moon, and Last Quarter are defined to occur when the excess of the apparent ecliptic (celestial) longitude of the Moon over that of the Sun is 0, 90, 180, and 270 degrees, respectively. These definitions are used when the dates and times of the phases are computed for almanacs, calendars, etc. Because the difference between the ecliptic longitudes of the Moon and Sun is a monotonically and rapidly increasing quantity, the dates and times of the phases of the Moon computed this way are instantaneous and well defined.

The percent of the Moon's surface illuminated is a more refined, quantitative description of the Moon's appearance than is the phase. Considering the Moon as a circular disk, the ratio of the area illuminated by direct sunlight to its total area is the fraction of the Moon's surface illuminated; multiplied by 100, it is the percent illuminated. At New Moon the percent illuminated is 0; at First and Last Quarters it is 50%; and at Full Moon it is 100%. During the crescent phases the percent illuminated is between 0 and 50% and during gibbous phases it is between 50% and 100%.

For practical purposes, phases of the Moon and the percent of the Moon illuminated are independent of the location on the Earth from where the Moon is observed. That is, all the phases occur at the same time regardless of the observer's position.

Answer 2

The moon orbits the earth, making one orbit very 29.2 days.
The sun rises and sets because the earth is spinning.
The moon also rises and sets because of the earth's rotation.
When we see the moon, the brightness we see is because the sun is shining on the moon.
At new moon, the sun and the moon rise and set at the same time and the moon is between the sun and the earth.
For this reason we can only see an outline of the moon at new moon.
Later, when the moon is in its first quarter, the moon rises several hours after the sun. When the sun sets, it shines back on the moon(which is high in the sky). The part illuminated by the sun is what we see.
At full moon, the sun and the moon are separated by 180 degrees.
This means that as the sun sets, the moon is just starting to rise. The sun shines straight back on the moon and illuminates the whole side of the moon, so it looks like a complete, illuminated circle. After full moon, the angle between the moon and the sun lessens, so the part of the moon which is lit up becomes smaller and smaller until at new moon, (29.2 days from the last new moon), the moon is a sliver once again .

To see how this works, try this experiment.
Set up a small lamp with one bulb and no lamp shade in a dark room. Get a white rubber ball or a smooth wooden ball
to use as the moon. Hold the ball between you and the light. What does it look like? This represents new moon.
Now slowly rotate the ball around the lamp. See how the "phases of the moon " change. Where are the shadows? How much is lit up? When the lamp is between you and the ball, this is "full" moon. See how the bulb lights up the whole side of the ball so it looks "full"?
If you do this carefully you will be able to see how the phases of the moon change throughout the whole cycle.
I hope this helps you understand the phases of the moon.

Answer 3

Lunar phases depend on the relative positions of the Earth, Moon and Sun. At full moon,the Earth is positioned between the Sun and the Moon,so the side of the Moon facing Earth is fully lit up by the Sun. At half Moon, the moon is situated at 90 degrees to the Earth,so we are able to view part of the Lunar surface illuminated by the Sun and the part in shadow. At New moon, the Moon lies between the Sun and the Earth,so the shaded portion of the Moon is facing the Earth. The intermediate phases (such as quarter moon,etc) are caused in the same way,but to greater or lesser degrees.

Answer 4

THE LAST QUARTER MOON phase (271d-315d) is akin to the seed pods coming to a head on the mature plant. Astrologers associate this phase with Saturn, which constructs, and with Uranus, which transforms the life essence. Many rebels and political radicals who give birth to revolutionary ideas are born under the last quarter. What the individual does now is likely to be recapitulated under the later cycle during the next new Moon incarnation. I guess this means that whatever I do in this life will pay off in the next because it is THE BALSAMIC MOON or WANING CRESCENT MOON phase (316d-359d) which represents the end of the karmic round and after that onto a new cycle of experience.

Answer 5

Simply: The moon revolves around the earth while the sun illuminates 50% of it. Therefore we are always seeing it for a different angle.

Answer 6

................ because of the rotation of the earth ................