why do we see different phases of the moon

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:, 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.

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