Orion's Belt is an asterism of three stars that appear about midway in the constellation Orion the Hunter. The asterism is so called because it appears to form a belt in the hunter's outfit. It is one of the most famous asterisms used by amateur astronomers. Asterisms are patterns of stars of similar brightness. The stars may be part of a larger constellation or may be formed from stars in different constellations.
Spotting the belt is actually one of the easiest ways to find the constellation Orion itself, which is among the brightest and most prominent in the winter sky. The three stars that traditionally make up the belt are, from west to east: Mintaka, Alnilam and Alnitak. The names of the outer two both mean "belt" in Arabic, while Alnilam comes from an Arabic word that mean "string of pearls," which is the name of the whole asterism in Arabic, according to astronomer Jim Kaler.
Hanging down from Orion's Belt is his sword, which is made up of three fainter stars. The central "star" of the sword is actually the Orion Nebula (M42), a famous region of star birth. The Horsehead Nebula (IC 434), which is a swirl of dark dust in front of a bright nebula, is also nearby.
Looking north of the belt, Orion's “shoulders” are marked by Betelgeuse and Bellatrix and south, his “knees” are Saiph and Rigel.
Cultural references and notable features
“The only real legend that is sometimes referred to in Western Culture with Orion's Belt is the Three Kings,” said Tom Kerss, an astronomer with the Royal Observatory Greenwich, in a Space.com interview. This is a direct reference to the Biblical tale of the three kings who offered gifts to the Baby Christ shortly after his birth.
Because Orion's Belt is so easy to find in the sky, it can be used as a pointer to bring amateur astronomers to other interesting objects. Move northwest of the star complex and eventually the line will bring you to the Pleiades star cluster, a collection of dozens of stars that are sometimes called the Seven Sisters (after those that are the most easily visible to the naked eye.)
Following southwest of the stars will lead you to Sirius, the brightest star in the sky in both the Northern and Southern hemispheres. Part of its brightness in the sky comes because it is so close to us, just 8.7 light-years away.
Kerss said the shape is also interesting astronomically. Some of the stars themselves are physically close together (which is not always true of stars in the sky, which only appear to be nearby.)
Recent astronomical news
Although the Orion Nebula has been studied thoroughly by both amateur and professional astronomers, surprises continue with further observations.
In 2013, a Chilean European Southern Observatory telescope spotted signs of a cosmic "ribbon" in the nebula that is more than 1,000 light-years away. The track contains cold gas and dust, and astronomers also noted they may have found 15 young stars or protostars while making these observations.
Even closer looks at the nebula have revealed features such as this bow shock from the young star LL Ori, which is sending out wind that strikes gas leaving the heart of the star-forming region.