Speaking of pulsars, they are more accurate, than any of earths atomic clocks.
Secure and accurate time sources
Broadcasts using sound or radiation, from sources such as radio, bell towers, and astronomical phenomena, must send out the same value to every receiver. A remote beacon such as a pulsar has perfect security: the access structure is any party, and its complement, the attack structure, is the empty set. For human controlled broadcasts, the attack structure consists only of the broadcaster and the access structure is any receiver.
Natural broadcasts are thus immune to the problem (known in computer science as the Byzantine Generals problem) of a transmitter sending different values to different receivers. Indeed, distributed network researchers have gone to great lengths to recreate this simple property on the Internet with logical broadcast protocols. The results are incomplete and very inefficient compared to physical broadcasts.
Nature provides clocks that are oblivious to the malicious intentions of any outside parties and many orders of magnitude more accurate than random delays that face attackers on the Internet. If critical Internet servers were synchronized to natural clocks in a secure and timely fashion, they would be immune to attacks that relied on uncertainties in timing.
Pulsars overtake atomic clocks in accuracy after about 4 months.
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I'm going of topic for mentioning this, but did you know that Joy Division's
Unknown Pleasures cover,
is a drawing of radio waves generated by a pulsar named PSR 1919+21?