They are two measures of the same eclipse. Magnitude tells you what fraction of the Sun’s diameter the Moon covers, and obscuration what fraction of its surface: that is how NASA defines them. In Madrid, on 2 August 2027, the magnitude will be 0.88 and the obscuration 86.1%, and the second is the closer guide to how much light is lost. Where there is totality, obscuration is 100% and magnitude goes above 1, but there the IGN (Spain’s National Geographic Institute) and we don’t give the same figure: the IGN gives 1.07 to every municipality with totality, and we give between 1.0001 and 1.03. Both are correct; they follow different definitions.
Magnitude and obscuration, with examples
| Place | Magnitude (ours) | Obscuration | Totality (IGN) |
|---|---|---|---|
| Ceuta | 1.03 | 100% | 4 min 48 s |
| Tarifa | 1.0217 | 100% | 4 min 38 s |
| Melilla | 1.0213 | 100% | 4 min 34 s |
| Cádiz | 1.0074 | 100% | 2 min 54 s |
| Málaga | 1.0029 | 100% | 1 min 49 s |
| Casarabonela | 1.0001 | 100% | 10 s |
| Almería | 0.9994 | 99.9% | no |
| Granada | 0.9876 | 99.2% | no |
| Seville | 0.9788 | 98.4% | no |
| Madrid | 0.8777 | 86.1% | no |
| Barcelona | 0.842 | 81.6% | no |
| A Coruña | 0.778 | 73.4% | no |
In every partial eclipse in the table, obscuration stays below magnitude: with 0.88, Madrid gets 86.1%, and A Coruña, with 0.78, 73.4%. Close to 1 the two figures get so near each other that they mislead. Almería has 0.9994 and 99.9%, and no totality: a thread of Sun stays uncovered, which is why the glasses never come off there.
Inside the path, our magnitude tells you how far the Moon moves in front of the Sun. At the edge is Casarabonela, with 1.0001 and 10 s of totality; near the centre, Ceuta, with 1.03 and 4 min 48 s. Why some places get totality and others don’t is explained in our learn section.
Why the IGN gives 1.07 to every municipality with totality
NASA defines magnitude as the fraction of the Sun’s diameter covered by the Moon, but its eclipse catalogue adds that for total, annular and hybrid eclipses that value is really the ratio of the Moon’s apparent diameter to the Sun’s. Its table for the 2027 path gives that ratio point by point: 1.072 and 1.073 as the shadow crosses the Strait of Gibraltar, and 1.079 at the maximum, in Egypt.
The 1.07 that the IGN gives to all its municipalities with totality matches that ratio. It gives the same figure in Tarifa, with 4 min 38 s of totality, as in Casarabonela, with 10 s, and that only fits if it measures the size of the Moon against the size of the Sun, not how far the Moon moves in front of it. We publish the other figure, the fraction of the diameter covered at maximum at each place, which in the path ranges from 1.0001 to 1.03. For partial eclipses both sources use the same definition: the IGN gives Madrid 0.88, as we do. In its table, Almería comes out at 1.00 and has no totality: that is 0.9994 rounded to two decimal places. The differences between the four types of eclipse, and what magnitude each one has, are in total, annular and hybrid eclipses.
Why the IGN’s times are about 10 seconds earlier
In the 105 municipalities with totality, the IGN’s maximum comes between 5 and 15 seconds before ours, with a median of 10 s. In Tarifa, the IGN gives totality from 10:45:00 to 10:49:38; we give 10:45:11 to 10:49:39 (Spanish time, CEST, UTC+2). Ours agree with NASA’s and Wikipedia’s, and the IGN’s come a few seconds earlier than all of them. The IGN doesn’t explain the difference on its website, and we are not going to invent a reason for it. What we do know is that the offset is similar in every municipality and that in last summer’s eclipse the two sources agreed.
What eclipseando uses
In Spain we publish the IGN’s verdict and duration of totality, which is the official reference, and the times from our own engine (skyfield with the DE440s ephemeris), with the IGN’s times alongside on each town page. Outside Spain, the duration is also from our engine. For the glasses we combine the two sources: take them off at the later of the two start times for totality and put them back on at the earlier of the two end times. In Tarifa, that leaves safe totality between 10:45:11 and 10:49:38.
And what you see always has the last word: the filter comes off when the last flash disappears and goes back on with the first. Outside the path it never comes off. How to recognise that moment is explained in when to take off your eclipse glasses during totality.
Sources: Glossary of Solar Eclipse Terms — NASA (magnitude as a fraction of the diameter and obscuration as a fraction of the area); Key to Catalog of Solar Eclipses — NASA (for total, annular and hybrid eclipses, magnitude is the Moon/Sun diameter ratio); Path of the Total Solar Eclipse of 2027 Aug 02 — NASA (diameter ratio along the path); El eclipse total de Sol del 2 de agosto de 2027 — IGN (in Spanish: magnitudes, times and durations by municipality, in official time); eclipseando data (magnitudes, obscurations and times from the skyfield + DE440s engine, and the comparison with the IGN’s times in the 105 municipalities).
If you would like something to keep from the eclipse, the shop prints T-shirts, mugs and posters with the name of your town, the time of its maximum and its seconds of totality. See the merchandise →
Remember: never look at the Sun without proper eye protection (filters made to EN ISO 12312-2). The official reference for safe viewing in Spain is the IGN (in Spanish): eclipses.ign.es.