Look up on a clear night and you will see a bright red star sitting on the shoulder of the constellation Orion.

It is Betelgeuse and for hundreds of years astronomers have puzzled why its twinkle grows lighter and then dimmer over time.

But the mystery has finally been solved.

Betelgeuse has a companion star that pushes light-blocking dust out of the way, temporarily making the star glow more brightly.

The presence of the star, nicknamed “Betelbuddy”, had been theorised, but Nasa has spotted it for the first time using its Gemini North telescope, in Hawaii.

Steve Howell, a senior research scientist at the Nasa Ames Research Centre, in California, said: “Papers that predicted Betelgeuse’s companion believed that no one would likely ever be able to image it.

“Gemini North’s ability to obtain high angular resolutions and sharp contrasts allowed the companion of Betelgeuse to be directly detected.”