Beetle Juice will die soon

Orion, The Hunter is one of the most spectacular constellations in the winter sky.

The easiest way to find it is to start at the brightest, fiercely sparkling white star in the sky, Sirius and then scan up and to the right.

This will lead you to three equally spaced stars lying in a straight line pointing roughly in the direction of Sirius. These stars form Orion's belt. There is a sort of straggling of faint stars hanging down from the belt where a sword would hang.

From there it is easy to see the belt is about halfway down a rectangle of stars, which form Orion's body. The lower right star is Rigel, a bright, white star, and the top left star is red or orange.

Binoculars bring out star colours really well. It is usually referred to as Betelgeuse, but many years ago astronomer Patrick Moore consulted some experts on ancient tongues about this name.

He was told that the name has become highly corrupted and the nearest one can get to something reasonable now is Betelgeux, pronounced Bayteljurze, which does sound more ancient and astronomical than Beetle Juice.

At some point in the not too distant future, that discussion is going to become moot, because Betelgeux is very close to the end of its stellar life, and destined to end it in a spectacular explosion, a supernova.

For a few weeks, it will outshine all the other stars in our galaxy combined, and be easily visible in daylight. It will end up collapsing to form a neutron star, or perhaps even a black hole.

A star's life consists of three parts, rather like ours:

• Youth
• Maturity
• Old age.

The youth part consists of formation and settling down. Then, there is a period — the longest of the three — of stability and maturity. Astronomers refer to this period as the main sequence life of the star.

Finally, there is old age, which arises when the star starts to run out of fuel. For small stars, this consists of sneezing off the outer layers until all that is left is the core of the star, gradually cooling off. Big stars have more options.

When they run out of fuel, they shrink, driving up their core temperatures until they become hot enough for the waste products of previous energy production to provide more energy, enabling them to swell up again.

However, inevitably, the final result is the end of the fuel supply, collapse and a huge explosion where the star blows itself to bits, while compressing its core into a neutron star or black hole.

As stars approach the end of the line, they swell into red giant stars and become immensely brighter, squandering what's left of their fuel and bringing on the inevitable all the sooner.

Betelgeux is now at that point. It is currently shining about 100,000 times brighter than the Sun, and its end cannot be that far off, certainly in the next few thousand years.

In most cases, all the fuel a star will get to power its lifetime of shining it gets when it forms. However, paradoxically, the more fuel it starts with, the shorter its life will be.

For example, Betelgeux has about 12 times the mass of the Sun. During its main sequence life,it would have been about 1,500 times brighter than the Sun. Our Sun will have a lifetime of around 10 billion years.

Even if Betelgeux has more fuel than the Sun, during the main sequence part of its life, it was shining so much brighter than the Sun that its lifetime has to be much shorter, tens of millions of years.

There is another star in the same sort of situation. It is Antares, the brightest star in the constellation Scorpius, The Scorpion. It is visible during summer, low in the south. Like Betelgeux, it is red or orange, depending on your colour vision.

This means there is a supernova candidate star available for us to watch for in the summer and the winter. Just cast an occasional eye in their direction. When it happens you will notice it.

• Venus lies low in the southwest after sunset
• Mars rises in the early hours.
• The Moon will be full Jan. 10.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.