• Our article on stopped-light lasers pointed readers in the wrong direction (20 September, p 16): the address for Ortwin Hess’s paper is doi.org/v23.
• Contrary to our report, the eye-testing smartphone kit developed by Smart Vision Labs does not yet have a fixed price (20 September, p 21).
• We flipped up in our story of the sun’s strange behaviour (20 September, p 38). The star’s magnetic poles switch places every 11 years or so.
