Eclipse Magnitude vs Obscuration: What the Numbers Mean

Quick answer

Eclipse magnitude is the fraction of the Sun's diameter that the Moon covers; obscuration is the fraction of its area. They are not the same: at magnitude 0.5 the Moon spans half the Sun's width but hides only about 40% of its disc. A total eclipse has a magnitude of 1 or more, while obscuration can never pass 100%.

📘 Full definition✓ Reviewed 2026-10-27

Eclipse magnitude is the fraction of the Sun's diameter that the Moon covers at the height of a solar eclipse. Obscuration is a different measure: the fraction of the Sun's area that is hidden. The two are easily confused, and they can differ a lot. Because the overlap of two discs grows slowly at first, a magnitude of 0.5, with the Moon across half the Sun's width, hides only about 39% of its area, while a magnitude of 0.9 hides about 87%. Magnitude can also go above 1: at a total eclipse the Moon looks slightly larger than the Sun, and a magnitude of 1.05 means its disc is 5% wider. Obscuration, by contrast, stops at 100%. An annular eclipse has a magnitude just under 1, because the Moon looks slightly too small. Lunar eclipses use magnitude in the same way, for the share of the Moon's diameter inside Earth's umbra or penumbra. The percentages on Orbital Radar's solar eclipse pages are obscuration: the share of the Sun's disc that is hidden, which is closer to how much the daylight dims. Eclipse tables usually give the magnitude, while maps and news reports tend to quote the percentage of the Sun covered, which is the obscuration: a city said to get 90% coverage is talking about area, not width.

Magnitude

Share of width

can be above 1 at totality

Obscuration

Share of area

never above 100%

Magnitude 0.5

About 39% hidden

of the Sun's area

Madrid, 2 Aug 2027

86% hidden

obscuration at 10:51 CEST

Understanding Eclipse Magnitude

Width against area

For a Moon and Sun of the same apparent size, this is how the share of the Sun's width covered turns into the share of its area hidden. The gap is widest in the middle of a partial eclipse:

Magnitude (width)	Obscuration (area)
0.10	4%
0.25	14%
0.50	39%
0.75	69%
0.90	87%
1.00	100%

How much of the Sun is hidden on 2 August 2027

Obscuration at the height of the eclipse for cities inside and outside the path of totality. Each city page gives its own figure and the time of greatest eclipse:

City	Sun hidden	Greatest eclipse
Luxor	100% (total)	13:05 EEST
Cairo	95%	12:55 EEST
Lisbon	92%	09:44 WEST
Madrid	86%	10:51 CEST
Rome	74%	11:12 CEST
Paris	51%	11:01 CEST
London	42%	10:00 BST
Berlin	34%	11:13 CEST

Magnitude at lunar eclipses

A lunar eclipse's umbral magnitude is the share of the Moon's diameter inside Earth's umbra at mid-eclipse. Below 1 the eclipse is partial; above 1 the whole Moon is inside and the eclipse is total, and the deepest total lunar eclipses reach about 1.8. The penumbral magnitude measures the same for the penumbra, and it is the figure that says whether a penumbral eclipse will be noticeable at all.

Frequently Asked Questions

What is the difference between eclipse magnitude and obscuration? ▼

Magnitude measures how much of the Sun's diameter the Moon covers; obscuration measures how much of its area is hidden. At the same moment the two give different numbers: a magnitude of 0.5 corresponds to an obscuration of only about 39%.

What does an eclipse magnitude of more than 1 mean? ▼

That the Moon looks larger than the Sun, so it can cover it completely and the eclipse is total. A magnitude of 1.08 means the Moon's disc is 8% wider than the Sun's; the larger the figure, the longer totality can last.

How much of the Sun will be covered on 2 August 2027? ▼

All of it inside the path of totality. Outside it, about 92% in Lisbon, 86% in Madrid, 74% in Rome, 51% in Paris, 42% in London and 34% in Berlin, at the height of the eclipse. Every city page gives its own figure and times.

Is 90% coverage nearly as good as totality? ▼

No. With a tenth of the Sun still uncovered, the light is only partly dimmed, the sky stays blue and the corona remains invisible. Only at 100%, inside the path of totality, does the sky go dark, and eye protection is needed until then.

What magnitude does an annular eclipse have? ▼

Just under 1, because the Moon looks slightly smaller than the Sun. Its obscuration is lower still, typically 80 to 95%, because the ring of sunlight left around the Moon takes up part of the area.

Understanding Eclipse Magnitude

Width against area

How much of the Sun is hidden on 2 August 2027

Magnitude at lunar eclipses

Frequently Asked Questions

Sources & References