One step away from dark energy (Image: Royal Observatory Edinburgh/AAO/SPL)

LIGHT is the bedrock of astronomy, so it may come as a surprise that astronomers don’t have a very good handle on measurements of brightness. That is set to change, however, as the antiquated brightness scale undergoes a long-overdue upgrade that could help to reveal the true nature of dark energy.

More than 2000 years ago, the Greek astronomer Hipparchus devised a scale ranking the apparent brightness of different stars. Today, astronomers use much the same system, measuring brightness relative to a handful of standard reference stars. The trouble is, …