First Quarter
Roughly half of the visible lunar disk is illuminated while the Moon is about 90 degrees east of the Sun.
Astronomy
Roughly half of the visible lunar disk is illuminated while the Moon is about 90 degrees east of the Sun. Phase boundaries in an eight-part model are conventions applied to a continuous change in lunar illumination.
Modern symbolic interpretation
Often framed symbolically as a point of action, friction, decision, and adjustment.
This is an interpretive convention rather than a measured physical influence on human events.