Effect of The Magnitude On A Solar Eclipse
In an annular solar eclipse, the magnitude of the eclipse is the ratio between the apparent angular diameters of the Moon and that of the Sun during the eclipse, yielding a ratio less than 1.0.
In a total solar eclipse which also is a central eclipse, the magnitude is also the ratio between the apparent diameters of the Moon and of the Sun, but this time the ratio is 1.0 or bigger. If the total solar eclipse is non-central, the magnitude is a number between 1.0 and this ratio of apparent diameters.
In a partial solar eclipse, the magnitude of the eclipse is the fraction of the Sun's diameter occulted by the Moon at the time of maximum eclipse. The Moon's and Sun's apparent sizes are approximately the same, but both vary because the distance between Earth and Moon varies. (The distance between Earth and Sun also varies, but the effect is slight in comparison.)
When the magnitude of the eclipse is larger than one, the Moon's disk will completely cover the Sun's disk in the sky, and so the eclipse will be total. The path of totality (i.e. of the travelling shadow of the Moon cutting off all sunlight from reaching the Earth's surface) is a relatively narrow strip, at most a few hundreds of kilometers across.
When the magnitude of the eclipse is less than one, the disk of the Moon cannot completely cover the Sun. When the centers of the two disks are sufficiently aligned, a ring of sunlight remains visible around the Moon. This is called an annular eclipse, from Latin annulus, meaning "ring".
The eclipse magnitude varies not only between eclipses, but also during a given eclipse. It may happen that an eclipse starts out as annular, and then becomes total. The reverse is also possible. In very rare cases, the eclipse may proceed from annular, via total, back to annular. These mixed-type eclipses are called hybrid.
Also, as seen from one location, the momentary eclipse magnitude varies, being exactly 0.0 at the start of the eclipse, rising to some maximum value, and then decreasing to 0.0 at the end of the eclipse. When one says "the magnitude of the eclipse" without further specification, one usually means the maximum value of the magnitude of the eclipse.
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