Scheduled Maintenance

OSA will be performing scheduled maintenance on Monday (21 October) from 17:00 to 19:00 US EDT. We apologize for any inconvenience this may cause. Thank you for your patience as we improve our services.

If you need assistance, OSA's Customer Service can be reached at +1 202.416.1907 (Worldwide) +1 800.766.4672 (US/Canada) or by emailing us.

Customer Service is available from 08:30 to 18:00 US EDT, Monday through Friday.

OSA | Living History

A strontium-ion optical clock, National Physical Laboratory, UK.


Optical Clock

Atomic clocks based on the elements strontium and ytterbium may prove even more precise than cesium clocks, considered the most accurate time-keepers.

Precise time is especially important for GPS, radio astronomy, financial transactions and identifying changes in fundamental constants. (Photo: National Physical Laboratory)

(Courtesy of National Physical Laboratory)