A BASIC unit of cosmic distance just got a tad more precise.
Like the first centimetre on a cosmic ruler, the distance to the Large Magellanic Cloud (LMC), a small galaxy orbiting the Milky Way, is the basis for measuring how far away other objects are.
Now Grzegorz Pietrzynski of the University of Concepción in Chile and colleagues have pinned down that distance by watching binary stars. The dip in light when one star eclipses its partner can reveal the foreground star's size. Comparing this with the size of its disc in the sky gives its distance.
Using the average distance to eight LMC binaries, the team found that the LMC is 162,900 light years away, to a record accuracy of 2.2 per cent (Nature, doi.org/kp9).
This article appeared in print under the headline "Binary stars refine cosmic centimetre"
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