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.

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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)