The sky — astronomy

Orion: The Hunter of the Winter Sky

Orion is easy to recognise by three bright stars in a short, straight row: its belt. Around it you will find reddish Betelgeuse, blue-white Rigel and the Orion Nebula (M42), a star-forming cloud visible to the naked eye as a faint smudge in the hunter’s sword.

Orion is one of the most recognisable constellations and often the first one people learn to find. It is among the 88 constellations officially recognised by the International Astronomical Union (IAU), and it holds several of the most rewarding sights you can see with the naked eye or a small pair of binoculars.

How to recognise Orion

The best starting point is the belt: three stars in a straight line, almost evenly spaced and of similar brightness. Around them you can trace a shape like an hourglass or a large, slightly irregular rectangle.

In the Northern Hemisphere, Orion is most prominent on winter evenings. It rises in the east, climbs toward the south and sets in the west. The constellation sits close to the celestial equator, so it can be seen from both hemispheres. The difference is orientation: from the south, the figure appears upside down compared with the view that northern observers know.

The belt also works as a pointer. Extended down and to the left (toward the southeast on northern winter evenings), its line leads to Sirius, the brightest star in the night sky; see Sirius. In the opposite direction lies reddish Aldebaran in Taurus. General observing tips are in How to look at the sky.

The belt and the sword

The three belt stars are Alnitak, Alnilam and Mintaka. All are hot, blue-white stars, much larger and more luminous than the Sun. They look like a tidy row only from our point of view; in space they lie at different distances from us and are not neighbours in a tight line.

Mintaka, the westernmost belt star, sits almost exactly on the celestial equator. This is why Orion’s belt rises nearly due east and sets nearly due west, making it a handy natural compass.

Below the belt hangs a fainter vertical line of stars and glowing patches: the sword. Look carefully at the middle of it and you will notice that it is not quite a star but a tiny fuzzy glow. It is the best-known object in the constellation.

The Orion Nebula

The Orion Nebula, also called M42 (its number in Charles Messier’s catalogue), is a cloud of gas and dust where new stars are being born. It lies roughly 1,300 light-years away, making it one of the nearest large star-forming regions. A light-year is the distance light travels in one year.

To the naked eye M42 looks like a faint, blurred star. Even small binoculars reveal its misty glow, and a small telescope shows the cluster of young stars at its heart, the Trapezium (a tight group of four main stars). The intense radiation of these young, hot stars makes the surrounding gas shine.

The nebula has been studied by space telescopes including Hubble and James Webb. Images released by NASA and ESA reveal filaments of gas and dust and newborn stars in remarkable detail. Fainter neighbours in the constellation, such as the Horsehead Nebula and the Flame Nebula, are much harder to see and call for dark skies and suitable equipment; our guide Binoculars or telescope can help you choose.

Betelgeuse and Rigel

Two of Orion’s brightest stars mark opposite corners of the figure. Betelgeuse sits at the upper corner, on the left as seen from the Northern Hemisphere, and has a distinct reddish-orange colour. Rigel marks the lower corner on the opposite side and is blue-white.

Betelgeuse is a red supergiant: a huge, cool (by stellar standards) and evolved star whose brightness changes over time. In late 2019 and early 2020 it faded unusually deeply, an event nicknamed the Great Dimming. Astronomers link it to a cloud of dusty material that was ejected and temporarily blocked part of the star’s light. Astronomers expect Betelgeuse to end its life as a supernova one day, but the exact moment cannot be predicted and is most likely far in the future. More in Betelgeuse.

Rigel is a blue supergiant, very hot and luminous. It is farther from us, yet it shines brightly because it radiates an enormous amount of energy. The colour contrast between the two stars reflects their temperatures: cooler stars look reddish, hotter ones blue-white.

The myth of Orion

This is the cultural side of the story, not astronomy. In ancient Greek mythology Orion is a mighty hunter. Tellings differ: in one well-known version he is killed by a scorpion, which is why the two are never in the sky together. When the constellation Scorpius rises, Orion sets. Hunters, warriors and other figures are seen in this group of stars in many cultures around the world, simply because Orion’s bright stars are hard to miss.

Myths are lovely guides for the imagination, but they are not scientific facts. The stars of Orion are not really connected: their different distances show that the figure is only a pattern projected on our sky. That is what makes watching it so fascinating: we see a familiar shape where the Universe is far deeper than it looks.

Positions in Astronativa are astronomically exact. The interpretation is for inspiration. · Glossary · Terms · Privacy