You don’t need one per person: the American Astronomical Society (AAS) says a group can share a few, because the partial phase moves slowly and a quick look every few minutes is enough. There’s time: in Madrid, from 09:45:35 to 12:02:42, 2 h 17 min of the Sun with a bite taken out of it. But if there are children, or if you’ll be watching inside the path of totality, it’s better to have one each. And in any case, a spare. Times are mainland Spanish time (CEST, UTC+2).
What the AAS says: sharing is fine
The AAS puts it like this: “Not everyone in a family or other group of observers needs their own eclipse glasses or handheld solar viewer”. And it explains why: the partial phases move very slowly, so “there’s no point in watching continuously”, and a glance every few minutes is enough to follow the Moon across the Sun. Its conclusion: “There’s plenty of time to share a small number of solar viewers among a large group”.
From the first bite to the last, the eclipse lasts more than two hours all over Spain (our subtractions, rounded to the minute):
| City | Starts | Ends | Start to finish |
|---|---|---|---|
| Ceuta | 09:41:02 | 12:01:09 | 2 h 20 min |
| Málaga | 09:42:09 | 12:02:35 | 2 h 20 min |
| Seville | 09:41:35 | 12:00:00 | 2 h 18 min |
| Madrid | 09:45:35 | 12:02:42 | 2 h 17 min |
| Barcelona | 09:50:56 | 12:11:11 | 2 h 20 min |
| A Coruña | 09:46:05 | 11:55:05 | 2 h 09 min |
| Las Palmas de Gran Canaria (Canary Islands time) | 08:33:20 | 10:42:46 | 2 h 09 min |
Inside the path, totality falls in the middle of all that, the only spell without glasses. The detail for each place is in how long the eclipse lasts from start to finish.
When it’s worth having one each
With children. The AAS says: “Always supervise children using solar filters”. If a child has to wait for another to pass the glasses over, they wait with the Sun in front of them and nothing on. It’s easier if each child has their own pair, in their size, with an adult beside them; the details are in eclipse glasses for children.
Inside the path, around totality. In the last minutes before the Sun goes out, you’ll all want to look at once. And totality ends for everyone in the same second: the AAS asks everyone to put their filter back on “as soon as the bright Sun begins to reappear”. With shared glasses, whoever doesn’t have them at that moment has to look away. In Tarifa, the IGN (Spain’s National Geographic Institute) gives the end at 10:49:38: from that second, glasses on or eyes elsewhere. The times for each town are in when to take off eclipse glasses in totality.
If someone has binoculars or wants photos. Eclipse glasses are no use for that. NASA says it in capitals: “Do NOT use eclipse glasses or handheld viewers with cameras, binoculars, or telescopes”. The device needs its own filter, over the front lens, and that filter doesn’t count as another pair of glasses: solar filters for cameras and phones.
And a spare
The AAS has a rule for any filter: “Always inspect your solar filter before use; if scratched, punctured, torn, or otherwise damaged, discard it”. A pair that gets bent in a rucksack or scratched in the sand leaves someone unable to look, and one extra pair solves that.
Three examples, with the sums shown (the sums are ours):
| Who and where | How many |
|---|---|
| Four adults outside the path | Two pairs to take turns without rushing, plus a spare: 3 |
| Two adults and two children inside the path | One each, plus a spare: 5 |
| Ten adults inside the path | Ten plus one: 11. With fewer, when the Sun comes back, whoever has no glasses looks the other way |
If you’re a group with children, such as a summer camp, the numbers are in eclipse glasses for a school or summer camp.
Last summer’s, if they’re in good condition
The AAS sets three conditions for reusing glasses: that they are less than 10 years old, that their manufacturer had them tested by an accredited laboratory that confirmed they meet ISO 12312-2, and that their filters aren’t scratched, punctured, torn, coming away from the frame or damaged in any other way. If yours meet all that, they count. How to check them in a minute is in do eclipse glasses expire? (in Spanish).
To check new ones, there’s our guide to certified glasses. On Order your glasses you can ask for ours: cardboard, with the EN ISO 12312-2 certificate, along with the phone filter and packs for groups. We reply with the price and the delivery time.
Sources: AAS — How to View a Solar Eclipse Safely (not everyone needs their own glasses; the partial phase moves slowly; supervise children; filter back on as soon as the Sun reappears; inspect and discard a damaged filter; the three conditions for reusing glasses); NASA — Eclipse Viewing Safety (eclipse glasses are not to be used with cameras, binoculars or telescopes); start and end times: eclipseando data (skyfield engine + DE440s); end of totality in Tarifa: IGN.
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.