What Is the First Quarter of the Moon's Cycle?

By Sean Tvelia

The moon lunar phases is actually caused by the placement of the moon relative, relative to the earth and sun. Find out about the first quarter of the moon's cycle with help from an Associate Professor of Geology at Suffolk County Community College in this free video clip.

Transcript

I'm Sean Tvelia, and we're here at Suffolk County Community College to determine what is the first quarter of the moon. The moon lunar phases is actually caused by the placement of the moon relative, relative to the earth and sun. At any one time, half of the moon is always lit by the sun. Now, what we see on the earth depends on where the moon is located in reference to the sun. As the moon travels around the earth, it moves from a position directly between the earth and the sun, a period that we would call a new moon, where the back of the moon is lit so we can't see it, all the way around 180 degrees to what we would call a full moon. As the moon moves through it cycle, different portions become visible to us on earth. As the moon arises about 90 degrees away from the sun, this half of the moon would be lit. As a result, we would see only a quarter of the moon showing us the first quarter of the moon. So, the first quarter of the moon is simply the time when one quarter of the moon is visible from our standpoint here on earth.

About the Author

Professor Sean Tvelia is an Associate Professor of Geology at Suffolk County Community College.