The star which has for centuries guided navigators across the globe appears to be coming to life once again after concerns that it brightness was fading away.

The star which has for centuries guided navigators across the globe appears to be coming to life once again after concerns that it brightness was fading away.

An international team of astronomers has observed that vibrations of the North Star, which had been fading away to almost nothing over the past 100 years, have recovered and are now increasing.

The discovery will be announced today on the first day of the Cool Stars 15 conference at the University of St Andrews.

Dr Alan Penny, from the School of Physics and Astronomy, will present results of the recovery to 350 international delegates at the meeting that runs from today until July 25.

The astronomers were watching The North Star, which sits overhead to an observer at the Earth's North Pole and which is currently the Polaris star, in the expectation that they would catch the star ceasing to vibrate when they made the surprising observation of its revival.

Dr Penny explained: "It was only through an innovative use of two small relatively unknown telescopes in space and a telescope in Arizona that we were able to discover and follow this star's recovery."

Team leader Dr Hans Bruntt, of the University of Sydney, Australia, had been using a small telescope attached to Nasa's now defunct infrared space telescope (Wire) to study the star for a short period of time and his data could be cross-checked with Dr Penny's.

Dr Penny said: "One hundred years ago Polaris varied by 10%, but over the last century the variations became smaller and smaller until 10 years ago it only varied by 2%. It was thought the structure of the star was changing to switch off the vibration.

"Yet the team has found that about 10 years ago the vibrations started picking up and are now back up at the 4% level."

Astronomers thought that Polaris was ageing and its structure was changing so that it was no longer unstable. This was being followed to learn more about how stars age.

Now Polaris has "turned on" again this explanation seems unlikely and there may be a complex process in the outer layers of the star.

Polaris is 430 light-years from Earth.

The North Star is visible only in northern hemisphere skies.