Orion the hunter is a signpost to half the winter sky
Few star patterns are as easy to spot as Orion, an hourglass of bright stars pinched by a neat row of three. Named for a hunter of Greek myth and catalogued by Ptolemy in the second century AD, it dominates northern winter evenings and works as a pointer to many of the sky's brightest stars.
Follow the three belt stars southeast and they lead to Sirius; run the line the other way and you reach Aldebaran. A line across the hunter's shoulders heads toward Procyon, and one drawn from Rigel up through Betelgeuse aims at the twins Castor and Pollux. Orion shows best in the evening between January and April, which means summer for skywatchers south of the equator. From May to July it sits in the daytime sky and vanishes for most observers.
Its two brightest stars make a vivid contrast. Betelgeuse, the hunter's right shoulder, is a red supergiant near the end of its life whose brightness wavers; it is usually the 11th brightest star in the night sky but slipped as low as 23rd by the end of 2019. When it finally explodes as a supernova, it could outshine the Moon and be visible in daylight. Rigel, a blue supergiant at the left foot, is the seventh brightest star overall and may meet a similar fate.
Distances within the figure differ wildly. Bellatrix, whose name means the female warrior, is the nearest major star at about 245 light-years, while Alnilam, the brightest and middle belt star, lies around 1,344 light-years away yet looks almost as bright as its neighbours. Mintaka, oddly, carries the Delta designation despite being the faintest of the three belt stars, and it is an eclipsing system whose light dips as one star passes in front of another.
Below the belt hangs the sword, and its middle point is not a star at all but the Orion Nebula, visible to the naked eye as a fuzzy smudge. Close to Alnitak, the dark Horsehead Nebula is shaped by a cloud of dust. All of these belong to a vast molecular cloud roughly 1,500 light-years distant, one of the busiest star nurseries visible from Earth. Every year around 20 October, the Orionid meteor shower, debris from Halley's Comet, reaches its peak, with up to 20 meteors an hour.
Source: Orion (constellation)
