STAGE PICTURE SHAPES FULL

If you were to view the moon cycling the earth from outside our solar system (the viewpoint of the stars), the time required is 27.3217 days, roughly two days less. The time required for the moon to move to the same position (same phase) as seen by an observer on earth is called the synodic period or lunation and it is 29.5305882 days on average (+/- 0.27 days due to the varying distance between the earth and the moon). That's true, but it's not exactly one month. You may have personally observed that the moon goes through a complete moon phases cycle in about one month. Following the third quarter is the waning crescent, which wanes until the light is completely gone - a new moon.

STAGE PICTURE SHAPES FULL

After the full moon (maximum illumination), the light continually decreases. After the first quarter, the sunlit portion is still increasing, but now it is more than half, so it is waxing gibbous. Thus you can simply combine the two words to create the phase name, as follows:Īfter the new moon, the sunlit portion is increasing, but less than half, so it is waxing crescent. Waxing essentially means 'growing' or expanding in illumination, and waning means 'shrinking' or decreasing in illumination. The word gibbous refers to phases where the moon is more than half illuminated. The word crescent refers to the phases where the moon is less than half illuminated. Once you understand those four key moon phases, the phases between should be fairly easy to visualize, as the illuminated portion gradually transitions between them.Īn easy way to remember and understand those 'between' lunar phase names is by breaking out and defining 4 words: crescent, gibbous, waxing, and waning. So we are seeing exactly half of the moon illuminated and half in shadow. 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. The shadowed portion is entirely hidden from view. The entire illuminated portion of the moon is on the back side of the moon, the half that we cannot see.Īt 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 three objects are in approximate alignment (why 'approximate' is explained below). 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.Īs shown in the above diagram, the new moon occurs when the moon is positioned between the earth and sun. If you'd like to examine the phases of the moon more closely, via computer software, you may be interested in this moon phases calendar software. So the basic explanation is that the lunar phases are created by changing angles (relative positions) of the earth, the moon and the sun, as the moon orbits the earth. Finally, please realize this diagram is only meant to demonstrate how the phases work the small inner moons in the diagram do not show the fact that the same side of the moon always faces Earth. Also note that the shadowed part of the moon is invisible to the naked eye in the diagram above, it is only shown for clarification purposes. At certain times we see both the sunlit portion and the shadowed portion - and that creates the various moon phase shapes we are all familiar with. Of course that is perfectly logical, but you need to visualize it in order to understand the phases. One important thing to notice is that exactly one half of the moon is always illuminated by the sun. When you do this, you'll 'see' that the illuminated portion is on your left, just as you see in the large image. For the waning gibbous, third quarter, and waning crescent phases you have to mentally turn yourself upside down when imagining the line of sight. The large moon image shows what you would see at that point in the cycle. The dotted line from the earth to the moon represents your line of sight when looking at the moon. The moon phase name is shown alongside the image. The moon is shown at 8 key stages during its revolution around the earth. The earth, of course, is at the center of the diagram. Sunlight is shown coming in from the right. The illustration may look a little complex at first, but it's easy to explain.

Stage picture shapes