The beautiful symmetry of a total solar eclipse happens because —by pure chance— the sun is 400 times larger than the moon, but is also 400 times farther from Earth, making the two bodies appear the exact same size in the sky.
All the solar eclipses will be annular, with the moon not quite big enough to cover the sun completely. Bottom line: The sun’s diameter is about 400 times larger than that of the moon – and the sun is also about 400 times farther from Earth. So the sun and moon appear nearly the same size as seen from Earth.