Draw a Moon Phase and Terminator Diagram

Moon Terminator draws an idealized lunar disk using a cycle angle: 0° is new Moon, 90° first quarter, 180° full Moon, and 270° last quarter. This angle is a position around the illustrated cycle, not the astronomical Sun–Moon–observer phase angle. Rotation turns the whole drawing without changing the illuminated fraction. It is a geometry aid, not a prediction for a date, location, horizon or photograph; real sky orientation needs those details.

How to use Moon Terminator

1. Choose a named phase or enter a cycle angle from 0° to 360° and a diagram rotation from −180° to 180°.
2. Select Draw diagram to see the lit shape, phase name and calculated illuminated percentage. Change either input and draw again to compare.
3. Download the displayed diagram as an SVG, or reset the inputs to start another comparison.