“The glasses you use must comply with the ISO 12312-2 international safety standard. Glasses that have reached this safety standard will have the ISO standard printed on them, and they will have a manufacturer’s report showing their compliance based on rigorous testing. They must also be free of any perforations or folds in the silvered lenses, as any damage to them risks making them unsafe to use,” Dr Greg Brown, astronomer at the Royal Observatory Greenwich, explains.