Shakespeare referred to it as the 'constant' North Star but astronomers from the University of Sydney's School of Physics have discovered that Polaris is not as predictable as first thought.

Known as a Cepheid variable or unstable star, Polaris's vibration changes as much as a celebrity on a weight loss program. Over the last one hundred years astronomers have been captivated by Polaris' intriguing changes as its vibration decreased from ten percent around 1900, down to two percent at the end of the millennium. This was thought to signify that Polaris was evolving, becoming stable as it was destined for the galactic graveyard.

"So our new results are quite unexpected. Our data clearly shows a return of the vibrations over the last five years" explains Dr Bruntt. "It's very rare you see a fundamental change in a star over such a short period of time."

Polaris is a super-giant star - 46 times the size of the Sun - and has burned very brightly using all its Hydrogen fuel up quickly, as a James Dean of stars - living fast and dying young. "We are quite puzzled by its new behaviour. Maybe it didn't want to grow old," says Dr Stello with a smile.

In paparazzi style, the astronomy team from six institutions across Australia, US and UK used three different telescopes to track the star's erratic personality. They made innovative use of a 'recycled' NASA satellite - WIRE - destined for the scrap heap after the failure of the main telescope. Dr Bruntt explains, "Using its smaller five-centimetre star tracker camera meant we could observe Polaris for weeks at a time, taking ten high-precision images per second."

With a second source of data from the SMEI instrument on the Coriolis satellite, built to observe mass being ejected from the Sun, Dr Bruntt and his team could pick Polaris out as a 'face in the crowd' scoring a picture of the North Star every 90 minutes over four years. To further enhance the multi-faceted perspective the team used ground-based measurements from the Tennessee Automatic Spectroscopic Telescope to measure the movement of the surface of Polaris as it waxes and wanes over its four-day vibration cycle.

Watching its unstable performance in the night sky Polaris has earned true celebrity status fascinating astronomers the world over. One thing's for certain, this will be one finale worth watching.

The results will be presented at the COOL stars conference at St Andrew's in Scotland on Monday 21 July 2008.