Have you ever wondered what causes the moon phases? We all know that its appearance changes over time. But why? The good way to understand the phases of the moon is to examine an earth-moon-sun diagram: 

 It's probably easiest to understand the moon cycle in this order: new moon and full moon, first quarter and third quarter, and the phases in between.

As shown in the above diagram, the new moon occurs when the moon is positioned between the earth and sun. The three objects are in approximate alignment (why "approximate" is explained below). The entire illuminated portion of the moon is on the back side of the moon, the half that we cannot see.

At a full moon, the earth, moon, and sun are in approximate alignment, just as the new moon, but the moon is on the opposite side of the earth, so the entire sunlit part of the moon is facing us. The shadowed portion is entirely hidden from view.

The first quarter and third quarter moons (both often called a "half moon"), happen when the moon is at a 90 degree angle with respect to the earth and sun. So we are seeing exactly half of the moon illuminated and half in shadow.

A solar eclipse is arguably one of the most thrilling sights on Earth. 

It occurs when the moon moves in front of the Sun.  A solar eclipse happens slowly as the Moon starts its trip across the Sun. It begins like it is taking a small bite out of the Sun. 

As the Moon gets closer to the center of the Sun the darkness occurs more quickly.  While a small crescent of the sun stays in the sky you can observe a unusual phenomenon with a solar eclipse - thin wavy lines appear that are light and dark that can be seen on light colored surfaces. These are called shadow bands and are caused by the distortion of Earth's atmosphere.

The Last String of Light Before Darkness

When the Moon has nearly blocked out the sun at the last few minutes before the total solar eclipse, you will see some points of light surrounding the edges of the dark Moon. These look like a string of beads wrapped around the edges and are appropriately called Baily's Beads. They are named after the astronomer Francis Baily who first noticed them in the 18th century. These beads only appear for a few brief minutes before the total solar eclipse occurs.

Beautiful Darkness Descends

When the Moon finally obscures the Sun completely, darkness occurs on Earth during the day. It is not quite like the darkness of night but more of a surreal, almost soft darkness. The sky near the horizon still appears bright and this produces a reddish glow and some very unusual shadows. When the total solar eclipse finally arrives, it gives an unearthly appearance. There is a pinkish glow, which comes from the edges of the moon before the total eclipse and sometimes a red cloud appearance arch above it. The pink glow is called Chromosphere and the red cloud is called solar prominence.