Magnitude of eclipse

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The magnitude of an eclipse is the fraction of the Sun’s or Moon’s apparent diameter that is blocked.

Solar eclipses
- Magnitude for partial or annular eclipses ranges from 0.0 to 1.0. Total solar eclipses have magnitude of 1.0 or more, with a practical maximum around 1.12. This is a ratio of diameters, not a measure of area or brightness.
- The Sun and Moon usually appear about 0.5 degrees across (roughly 30 arcminutes), but this changes as they move closer or farther away.
- Annular eclipse: magnitude is less than 1. The Moon doesn’t completely cover the Sun, so a ring of sunlight remains around the Moon (annulus).
- Total eclipse: magnitude is 1.0 or more, and the Sun is completely covered when the bodies align well enough. The path where you see totality is a narrow strip on Earth.
- Partial eclipse: magnitude is the fraction of the Sun’s diameter covered at the peak of the event.
- When people say “the magnitude of the eclipse,” they usually mean the maximum magnitude.
- Some eclipses are hybrid: seen as total from some places and annular from others.

Lunar eclipses
- Here the Moon is the eclipsed body and Earth’s shadow is the eclipsing body. The Earth’s shadow is always larger than the Moon at its distance, so lunar eclipses can be partial or total, but never annular.
- The shadow has two parts: the dark umbra and the brighter penumbra.
- A lunar eclipse has two magnitudes: umbral magnitude (how much of the Moon goes into the dark shadow) and penumbral magnitude (how much of the Moon goes into the lighter shadow).
- If the Moon does not reach the umbra, it only passes through the penumbra, and the eclipse is penumbral.