A constellation you can find anywhere
Orion straddles the celestial equator, so people in almost every country can see it. From the northern hemisphere it rises in the east on autumn evenings and stands high in the south during winter. From the southern hemisphere it appears upside down compared with the chart above.
It is one of the 88 modern constellations and holds two of the ten brightest stars in the night sky. That is why it makes a good starting point for learning your way around.
The main stars
The two brightest stars have very different colours. Betelgeuse glows orange because its surface is cooler. Rigel is hot and shines blue-white.
| Star | Role in the figure | Distance | Type |
|---|---|---|---|
| Betelgeuse | Left shoulder | about 550 ly | Red supergiant |
| Rigel | Right foot | about 860 ly | Blue supergiant |
| Bellatrix | Right shoulder | about 250 ly | Blue giant |
| Saiph | Left knee | about 650 ly | Blue supergiant |
| Alnitak, Alnilam, Mintaka | The belt | 700 to 2,000 ly | Blue supergiants |
Betelgeuse is a variable star. Its brightness changes over months and years, and in 2019 and 2020 it dimmed far more than usual before recovering. Astronomers expect it to end as a supernova, though probably not for many thousands of years.
The Orion Nebula
Below the belt hangs a short line of faint stars called the sword. The middle one looks fuzzy because it is not a star at all. It is the Orion Nebula, also known as Messier 42, a cloud of gas and dust lit from within by young, hot stars.
The nebula is a stellar nursery. New stars are forming in it right now, and it is the closest large star-forming region to Earth. You can see it as a soft smudge with the naked eye on a dark night, and binoculars show its shape clearly.
Nearby sits the Horsehead Nebula, a dark column of dust shaped like a chess knight. It is much fainter and needs a telescope and a long exposure to photograph.
The myth of the Hunter
In Greek mythology Orion was a giant hunter, the son of Poseidon. Many versions of his story exist. In one, he boasted that he could kill every animal on Earth, and the goddess Gaia sent a scorpion to stop him. The scorpion won, and both were placed in the sky.
The constellation Scorpius is said to chase Orion across the heavens. It is a neat detail that the two are never above the horizon at the same time. When Scorpius rises in the east, Orion sets in the west.
Other cultures saw different pictures in the same stars. In parts of the ancient Near East it was a warrior or a king, and in several traditions the three belt stars were three sisters, three kings, or a row of seeds.
How to find Orion
- Go outside on a clear evening between December and February and face south if you are in the northern hemisphere.
- Look for three medium-bright stars in a short, even line. This is the belt.
- Find the bright orange star above and to the left, and the bright blue-white star below and to the right. These are Betelgeuse and Rigel.
- Extend the belt line downward to the left to reach Sirius, the brightest star in the whole sky.
- Look below the belt for the sword, and point binoculars at its middle to see the nebula.
Each October, the Orionid meteor shower appears to come from the area just above Betelgeuse. It peaks around 21 October and is made of dust left behind by Halley's Comet.