Some Pulsars have extremely stable frequencies https://www.nytimes.com/1983/02/09/us/pulsar-termed-most-accurate-clock-in-sky.html https://www.nytimes.com/1983

Some Pulsars have extremely stable frequencies https://www.nytimes.com/1983/02/09/us/pulsar-termed-most-accurate-clock-in-sky.html https://www.nytimes.com/1983/02/09/us/pulsar-termed-most-acc...