Hit eclipse button. Observe size fluctuation. Flag to see moon and sun side by side. Turn off rotations if it helps you focus on size fluctuations. Sun is about 400 X larger than moon, but 400 X farther, so sun & moon seem about the same size! But, elliptical orbits create fluctuation of apparent sizes, over a little less than a month. The model speeds up that fluctuation.
Moon size fluctuates a bit more than the sun does. Sun's angular diameter changes from 0.53° to 0.55° Moon's angular diameter changes from 0.49° to 0.56° Those measure the apparent diameter with angles assuming the full visible sky dome is 180°. The Sun rotates once every 24 earth days (rotation of this hot plasma is at its equator). Moon rotates once every 27.3 earth days but also orbits earth 27.3 earth days. So, moon rotates yet, because it orbits during the same period, the same side of moon always faces earth. A moon day is 29.5 earth days, and all sides of moon get some sun ("dark side" just means the side facing away from us).
