Famous the world over, Betelgeuse is a star that anyone who’s stared at the Constellation Orion will be at least vaguely aware of.
Betelgeuse is star number four, also to be thought of as Orion’s left shoulder, and this bright star is usually the second-brightest of Orion, though occasionally, it becomes the brightest. This is because Betelgeuse is a variable star, subject to peaks and troughs in its luminosity. It is classed as a red supergiant, and is thought to be between 16-19 times more massive than the Sun. Its radius is difficult to pin down, as the star is misshapen and changes over time, but it is thought to be as large as the orbit of Mars. Betelgeuse truly is a behemoth, though more massive and larger stars exist.
Because of its brightness, Betelgeuse has fascinated astronomers since ancient times. Ancient Chinese astronomers noted a yellow colour to the star, and given that massive stars go through different phases, it could well have been in such a state at some stage. The Romans determined it to be orange, several hundred years later. In 1920, Betelgeuse became only the second star (after the Sun) to have its angular diameter measured. More recently, Betelgeuse has been imaged in some detail, with the uneven shape of this pulsating giant being revealed in numerous pictures.
A lot of modern-day interest in Betelgeuse comes from its future prospects. Betelgeuse is expected to explode as a supernova in the astronomically near future, though that could be hundreds, thousands, or even tens of thousands of years from now. It might even be hundreds of thousands of years away. There is a lot of uncertainty about the star’s properties (some estimates place the mass as low as seven solar masses), and the variable nature of the star makes pinning down its size difficult. As the precise distance is also tricky to determine, there are a lot of unknowns about the star’s immediate future.
One thing is fairly certain. Betelgeuse’s death will be very-much visible from earth.