It's Memorial Day, Short Wavers. This holiday, we bring you a meditation on time ... and clocks. There are hundreds of atomic clocks in orbit right now, perched on satellites all over Earth. We depend on them for GPS location, Internet timing, stock trading and even space navigation. In today's encore episode, hosts Emily Kwong and Regina G. Barber learn how to build a better clock. In order to do that, they ask: How do atomic clocks really work, anyway? What makes a clock precise? And how could that process be improved for even greater accuracy?

- For more about Holly's Optical Atomic Strontium Ion Clock, check out the OASIC project on NASA's website.
- For more about the Longitude Problem, check out Dava Sobel's book, Longitude.

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