the Moon swings between the Earth and the Sun, it's in the sky all day
with its dark side facing us. Normally we can't see it. When the alignment
is precise, the Moon partially or fully obscures the disk of the Sun, which
allows us to see the Moon silhouetted against the Sun. Only when the Sun's
disk is fully obscured can the new moon be observed safely with the naked
eye, backlit by the Sun's corona during a total eclipse.