why do we see the moon phases

The phases of the moon, as seen from the earth, are a result of the angle the moon has in relation to the sun. A fact we must remember is that the moon does not have its own light, thus what we see is sunlight reflected from the surface of the moon. The moon revolves around earth and completes one cycle in about a month (around 30 days). During this revolution, a combination of the moon's angle with sun and the reflection of sunlight from moon's surface causes the phases. The moon's phases start with the new moon. After that, the moon starts (as it appears from earth) to grow, or wax, as it moves away from this position, and we see progressively more of the sunlit side of moon. We move from new moon to one-quarter moon and then to full moon (when we see the complete sunlit side of the moon). After that, it starts to appear thinner, or wane, with each day and crosses over from three-quarter moon finally to new moon again.


Some people wrongly think that the new moon is an eclipse of the moon, when the shadow of earth falls on the moon because of sun-earth-moon alignment. This is not true. The reason it is not true is because the moon has an orbit that is not on earth's ecliptic, or orbital plane. There are between four and seven eclipses of the moon each year, and there are 12 new moon phases, so eclipses and new moons can't be the same. Note that irrespective of what we see from earth, the moon is always lit by the sun, it's just that we are unable to see it fully because of the angles. Hope this helps.
For millennia, humans have kept track of time by observing the changing face of the moon. In fact, you may have noticed that the word moon shares its first few letters with the word month and that s no coincidence. The phases of the moon new moon, first quarter, full moon and last quarter repeat themselves about once every month.


But why does the moon have phases at all? To answer this question, it s necessary to understand two important facts. First of all, the moon revolves around the Earth once every 29. 5 days. And secondly, as the moon carries out its voyage around the planet, it s lit from varying angles by the sun. One half of the moon is always illuminated by the sun. But here on Earth, we can t always see the half of the moon that s lit up. What we call the phases of the moon represent the different fractions of the moon s lighted half that we can see as the moon circles the Earth. [ When the moon and the sun are on opposite sides of the Earth, we perceive the moon as full. However, when the sun and the moon are on the same side of the Earth, we say the moon is new. During a new moon, the side of the moon that we can see from Earth is not at all.


Between the new moon and, the moon is a crescent (less than half illuminated). It then waxes grows bigger into a half-moon (half-illuminated). The first half moon after the new moon is called the first quarter because at that point, the moon is one-quarter of the way through its monthly cycle of phases. After the first quarter comes the gibbous moon (more than half illuminated) and finally a full moon. This cycle of phases then repeats itself in reverse. After a full moon, the moon wanes becomes smaller into a gibbous moon, a half-moon (also called last quarter), a crescent and finally a new moon. Just before and just after the new moon, when a slim crescent of the moon is lit, you can also see the rest of the moon lit dimly. This owes to sunlight that bounces off the Earth and illuminates the otherwise dark portion of the moon that s facing us, an effect known as earthshine.


The major phases of the moon new moon, first quarter, full moon, last quarter and next new moon occur, on average, about 7. 4 days apart. If you need some help tracking these phases yourself (or if you want to see where the moon was on an important day in history), NASA provides an of the dates and times of all phases of the moon for the six thousand year period between 2000 BCE to 4000 CE. NASA s, a coalition of amateur astronomy clubs from around the U. S. , also provides information that may be helpful to those who want to know more about the phases of the moon and the solar system in general. , provided by the Astronomical Society of the Pacific, demonstrates why the moon has phases. Follow Elizabeth Palermo on Twitter @ techEpalermo, Facebook or Google+. Follow LiveScience @livescience. We re also on Facebook Google+. More information about why the moon has phases:

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