why do we see the moon in different phases

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: Asked by Brian Baur The phases of the Moon that we see are caused by the relative positions of the Sun, Moon and Earth. The phase of the Moon is defined by the proportion of the Moon lit up by the Sun that is visible from Earth.


Over the 24 hour period that it takes for the Earth to spin so that all areas can see the Moon, these relative positions wouldnвt alter enough to see a different phase of the Moon around the world. However the Moon does not look completely identical from every location on Earth; depending how far South or North you are (your latitudinal position) the Moon appears to be rotated. In the northern hemisphere the sunlit part of the Moon travels from right to left while from the southern hemisphere the light appears to travel from left to right. This is simply down to the differing angles you are observing the Moon from. Answered by Megan Whewell, Education Team Presenter for the Tags:,

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