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The phase (or magnitude) of a solar eclipse reflects how deep the Moon eclipses the Sun. The larger the phase is, the larger proportion of the Sun is covered. However, do not mistaken the phase for the covered area ratio. Their definition are shown below respectively:

Phase of solar eclipse = BC / AB

=  length of the covered portion (along the line passing through the centres of the Sun and the Moon) ÷ the Sun's apparent diameter

length of the covered portion(BC), the Sun's apparent diameter(AB)

 
Covered area ratio = covered area ÷ area of the solar disc

Phase Covered Area Ratio
0 0
0.1 0.127
0.2 0.253
0.3 0.376
0.4 0.495
0.5 0.609
0.6 0.715
0.7 0.812
0.8 0.896
0.9 0.963
1.0 1.000