Why is there phases of the moon

At times, our Moon reflects so much light that it makes viewing parts of the night sky challenging! Our Moon's shape doesn't really change — it only appears that way! The relative positions of our Sun, Earth, and Moon, cause these changes. As our Moon orbits around Earth, the side facing the Sun is always illuminated, just like Earth's daylight side is illuminated by the Sun.

What we see from Earth , however, is a different story. From Earth, the Moon's surface looks dark because the illuminated side is facing away from Earth. Between the new and full Moon, the amount of Moon we see grows — or waxes from its right side toward its left side.

As it passes the full Moon stage, the amount of illumination decreases — or wanes — from right to left. Finally, the Moon returns to its position between the Earth and the Sun, and on Earth we observe the new Moon again. In the southern hemisphere, illumination of the Moon increases from the left to the right side in the waxing phase and the dark part increases in coverage from left to right in the waning phase, which is opposite of the northern hemisphere.

No matter where on Earth an observer is, however, the phases of the Moon occur at the same time. What causes a lunar eclipse? Pictures of the Moon's phases often make it look like there should be a lunar eclipse during each full Moon and a solar eclipse during each new Moon. However, two things have to happen for a full lunar eclipse.

First, the Moon has to be full, so there is only an opportunity for a lunar eclipse about once each month. Second, the Moon has to pass through Earth's shadow.

This means that most of the time the Moon is slightly above or below Earth's plane of orbit — and out of the shadow cast by Earth where it blocks the Sun's light.

No eclipse occurs during these full Moons. 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.

Between the new moon and the full moon , 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. When the Moon appears half full, it has then reached its First Quarter.

Naturally, the Moon then starts to get smaller and smaller as it moves back towards the sun. It reaches Last Quarter when it looks empty. Finally, it goes dark and returns to a New Moon. The lunar cycle, which means it is going from one New Moon to another New Moon, takes about 30 days to complete. That means all the phases happen once a month. Instead, we only see a change in shape because we can only see the parts of the Moon that are being lit by the Sun.

The parts we do not see are simply in darkness or shadow. The phases of the Moon are easy to understand once you realise and remember that the phases are dependent upon the location of the Sun, Moon, and Earth.

The phases occur because the Sun lights different parts of the Moon as the Moon revolves around the Earth.