How do you find Orion?

Orion's Belt is three fairly bright stars, evenly spaced in a line. From west to east they are Mintaka, Alnilam and Alnitak. The row is short: three fingers held at arm's length will cover it.

Around the Belt, four bright stars make a tall box, like the outline of an hourglass: Betelgeuse and Bellatrix at the shoulders, Rigel and Saiph at the knees. Below the Belt hangs a shorter line of fainter stars, the Sword.

The Belt lies almost exactly on the celestial equator, the line in the sky above Earth's equator. That means Orion can be seen from almost everywhere on Earth. It also means the Belt rises due east and sets due west, wherever you are.

Orion is a good test of how dark your sky is. From a city centre you may see little more than the Belt and the brightest stars around it. Under a dark sky the whole figure fills in with fainter stars.

Orion is not up in the evening all year. As Earth travels around the Sun, the Sun passes in front of different stars, and the night side of Earth faces a slowly changing sky.

In the north, Orion appears in the east in the late evening during November. By midwinter it is up for most of the night, including early in the new year, when Earth makes its closest pass of the Sun, in 59d 12h 23m 23s. January to March are the best months for an evening look, with Orion due south in mid-evening during February. By April it sinks into the west after sunset, and from about mid-May to July it is lost in the Sun's glare. It returns before dawn in late summer.

The Southern Hemisphere shares the same calendar but turns Orion upside down. On a summer evening in Sydney or Cape Town, Orion stands high in the north on his head, with Rigel above Betelgeuse. Many Australians know the Belt and Sword as the Saucepan.

Earth carries you round the Sun at 29.78 kilometres per second. Since you opened this page, it has carried you 0 kilometres closer to the next evening with Orion in it.

Look closely and you can see that Orion's two brightest stars are different colours. Betelgeuse, at the top left as seen from the north, glows orange-red. Rigel, at the bottom right, is blue-white.

Both are supergiants, stars far larger and more powerful than the Sun. Betelgeuse is a red supergiant, so swollen that if it took the Sun's place it would reach beyond the orbit of Jupiter. Rigel is a blue supergiant and usually the brighter of the two, at magnitude 0.13. On the magnitude scale, which runs backwards, smaller numbers mean brighter stars. Betelgeuse changes: over the years it has ranged between 0 and 2, so it sometimes outshines Rigel.

The two stars look side by side, but they are not neighbours. Betelgeuse lies between 440 and 880 light-years away; astronomers still disagree on the exact figure. Rigel is between 790 and 1,030 light-years away. A constellation is a pattern seen from one place, Earth, not a group of stars that belong together.

Late in 2019, Betelgeuse began to fade. By February 2020 it had lost more than half its light, a change anyone could see by eye. Some people wondered whether it was about to explode. The real cause was closer to home: the star had thrown off a huge piece of its surface, which cooled into a cloud of dust and blocked some of its light. By 2023 it was back, and brighter than usual.

Betelgeuse will explode one day as a supernova. By the standards of a star's life, that is soon. By ours, it may not be. The usual estimate is that it is not likely for about another hundred thousand years. A few studies suggest it could be much sooner, within centuries. Put together, the time left is between 300 and 100,000 years, and experts disagree on where in that range the truth lies.

When it does happen, we will know. For about three months a point of light about as bright as a quarter Moon will shine where Betelgeuse was. It will then fade, but stay visible to the eye for years. Orion will have lost a shoulder.

Look at the middle star of Orion's Sword. Even with the eye alone, under a moderately dark sky, it looks slightly fuzzy. Binoculars show why: it is not a star but a glowing cloud of gas and dust, the Orion Nebula.

The nebula is a nursery. Hundreds of new stars are forming inside it, and at its heart four young, hot stars, the Trapezium, light up the gas around them. A small telescope shows them as a tight little group.

The Orion Nebula is one of the nearest places where stars are being born, which makes it a natural laboratory for astronomers. The light reaching you tonight left the nebula about 1,300 years ago.

Our own Sun was probably born in a cloud like this, 4.6 billion years ago. When you look at the Orion Nebula, you are looking at something like our own beginnings.