Do you know how GPS works?

Basically, the satellites broadcast the time using very accurate clocks, and the differences in times received from various satellites in different positions allow a receiver to determine its positions.

Well, it looks like someone is on the cusp of using a natural clock to do the same thing, using pulsars: (paid subscription required)

Celestial navigation was a mainstay in the early days of aviation, and astronavigation is still used in nuclear bombers to overcome jamming. Now a European research project has shown the feasibility of employing pulsars for aircraft navigation that is independent of ground- or space-based equipment.

The PulsarPlane project is investigating the use of pulsar signals for real-time navigation and timing, to overcome the vulnerabilities of global navigation satellite systems and reduce operating costs for aviation in the second half of this century.

Begun in 2013 and funded by the European Union’s Framework 7 research program, the project is coordinated by the Dutch aerospace laboratory NLR and involves universities in the Netherlands, Finland, Portugal and Bulgaria.

Pulsars are fast-rotating neutron stars that emit stable, fast electromagnetic pulses with unique periods between 1.4 millisec and 5 sec. and unique shapes. Pulsars are visible from everywhere on Earth and across a wide band of frequencies.

This is insanely cook cool.