When the illuminated portion is decreasing from one night to the next, the moon is in its 'waning' phases.
When the Moon is "waxing", it is increasing in visible size. This is between the new moon to the full moon. When the Moon is "waning" it is decreasing in size, from the full moon to the new moon.
The waxing phase of the moon is the period of time between new moon and full moon, where the size of the illuminated portion of the moon is increasing. The waning phase of the moon is the period of time between full moon and new moon, where the size of the illuminated portion of the moon is decreasing.
When the moon appears to be decreasing in size, it is called waning. When the moon appears to be increasing in size, it is called waxing.
Under what circumstance is this visible?
The moon waxes when the amount you can see increases in size. The waxing moon lasts from a new moon to a full moon. Waning is when the illuminated part of the moon decreases in size. This happens during the time when a full moon becomes a new moon.
When the Moon is "waxing", it is increasing in visible size. This is between the new moon to the full moon. When the Moon is "waning" it is decreasing in size, from the full moon to the new moon.
The waxing phase of the moon is the period of time between new moon and full moon, where the size of the illuminated portion of the moon is increasing. The waning phase of the moon is the period of time between full moon and new moon, where the size of the illuminated portion of the moon is decreasing.
The waxing phase of the moon is the period of time between new moon and full moon, where the size of the illuminated portion of the moon is increasing. The waning phase of the moon is the period of time between full moon and new moon, where the size of the illuminated portion of the moon is decreasing.
When the moon appears to be decreasing in size, it is called waning. When the moon appears to be increasing in size, it is called waxing.
When the visible bright part of the Moon is increasing in size, the term "waxing" is used. When the visible part of the Moon is less and less illuminated each night, the term "waning" applies.
A gibbous moon is one of the phases of the Moon, when the size of the illuminated portion is greater than half but not a full Moon.
This is when the moon is "decreasing" in size. Moving from a full moon to a new one
Exactly 50% of the moon is illuminated at any moment. As the moon revolves around the earth and its position changes, the fraction of that illuminated 50% that's visible to us on earth changes.
Around 25% illuminated, depending on where you were when you saw it.(Your position doesn't affect the size of the illuminated portion, but as time went on during the night, the actual visible portion of the moon was shrinking.)
Under what circumstance is this visible?
I'm assuming that you are intending to ask, "What is the decreasing moon phase called?" When the moon is getting smaller, it's referred to as "waning". When the moon is increasing in size, it's referred to as "waxing".
A gibbous moon is one of the phases of the Moon, when the size of the illuminated portion is greater than half but not a full Moon.