The moon as seen from the earth is at about 382,400 kilometers away from us. It takes the moon 29.53 days in a lunar month to completely orbit the earth. The phases of the moon that we see is as result of the different angles the moon forms with the sun viewing it from the earth. The moon will go through many phases during these days of orbiting the earth. The journey of the moon around the earth creates some shadows and lights which are predictable. These variations in the sizes of the shadows and lights are referred to phases. The moon does not have a light of its own, but it is illuminated by the sun. The amount of illumination varies depending on the percentage of light illuminated by the sun. This illumination could get up 10 percent sometimes.
Four main moon phases currently exist which is the new moon, first quarter moon, full moon and the last quarter moon and they appear in that order. Three specific times when these phases occur. They can also be measured by the moon's luminosity. The distance further the moon is in its orbit around the earth can also be used to measure the phases.
This is usually the first moon phase observed. It occurs when the moon has zero percent luminosity. At this time, the moon is completely dark. The moon lines up between the sun and the earth. On the earth, we only see the dark side of the moon, which is not lit by the light from the sun. During this moon phase, an eclipse will occur when the moon and the sun exactly line up in a concentric circle.
This moon phase occurs some days after the new moon is seen. After the new moon, the moon continues to orbit the earth eastward away from the sun. Small illumination of the sun appears on the side of the moon each night. It appears in the shape of a crescent in the western side of the moon. As the days go by, the size of the crescent begins to increase or grow fatter. When the crescent becomes the half of the moon, it is called the first quarter moon. The half of moon’s disc is now illuminated by the sun. At this point, the moon has gone one-quarter of its way through the lunar moon, hence where the name “quarter” emanated from.
As the moon continues to orbit the earth, the shape continues to change as well. When the illumination is half of the disc, it has a shape called gibbous. This gibbous moon continues to grow fatter as each night passes. This goes on until the sunlit face of the moon shows, this is called the full moon. The moon has completed half of the lunar month at as this time when it rises just exactly when the sun sets. The moon also sets the same time the sun rises in the next day.
When the moon enters the second half of the journey into the lunar month, it begins to grow thinner each night as it illuminates less light from the sun. It is termed waning. As the moon is waning, the gibbous previous shape begins to grow thinner each night. By the time the moon gets to the three-quarter of the lunar month, one side of the disc is illuminated while the other remains in darkness. The side that was dark first quarter is illuminated at the last quarter. A waning crescent appears as it approaches another new moon. So, the circle continues within a 29.53 lunar month.
Besides the four major moon phase, there are some other minor moon phases that occur halfway between the points of two main phases. The minor moon phases do not have a specific or regular time or occurrence, unlike the major moon phases. These minor phases often describe the phase of the moon between two main phases. Some of these minor phases are waning crescent moon, waning gibbous moon, waxing gibbous moon, and waxing crescent moon.
Moon phase was first recorded as far back as the 500 BC by Pythagoras, the Greek astronomer, and philosopher. He studied the narrow boundary line between the dark and light hemispheres of the moon. This line is called a terminator. He was the first to confirm the moon to be a sphere. Aristotle, at 350 BC during a lunar eclipse observed the shadow of the earth on the face of the moon. He reaffirmed that the earth was also a sphere just like the moon. He also postulated that the moon was translucent to permit illumination of the sun to pass through. Nicolaus Copernicus and Galileo in the 16th Century developed a model that unraveled the mystery. With the use of the telescope and more knowledge aided them to get full details of the earth and moon.