Orion, the Hunter, is perhaps the most widely recognized of all constellations. In Greek mythology, Orion was a mighty hunter who triumphed over the mightiest beasts but fell victim to the bite of a lowly scorpion. To acknowledge this, the gods placed Orion and the constellation Scorpio on opposite sides of the sky so the two would never be visible simultaneously. In Hindu folklore, Orion was Prajapati, an incestuous creator deity who pursued his daughter, the dawn goddess, but was pierced by an arrow launched by the star Sirius. To the ancient Egyptians, Orion was the god Osiris, while Amazonian Indians saw Orion as a giant river turtle. This article will explore some of the stars and deep sky objects found in this fascinating constellation.
Orion straddles the celestial equator and is visible to sky watchers throughout the world for over six months out of each year. In mid-northern latitudes, Orion rises before midnight starting in late October and can be seen until the following April. The constellations bordering Orion include Taurus (the Bull) to the northeast, Gemini (the Twins) to the northwest, Canis Minor and Canis Major (Orion’s Dogs) to the east and southeast, Lepus (the Hare) immediately to the south and Eridanus (the River) to the southwest.
Stars
The brightest star in Orion is the blue supergiant Rigel (beta Orionis), but for some obscure reason, the red star Betelgeuse was given the alpha designation. Rigel (which means “foot” in Arabic and Hebrew), is located close to 800 light years away from Earth and marks the Hunter’s left leg. Rigel appears bluish white because its surface temperature is extremely hot – some 11,000 degrees Kelvin compared to 5,800 K for the Sun. Rigel is also 17 times more massive than the Sun and radiates over 60,000 times as much energy. Blue stars like Rigel have relatively short lifespans, as stars go; they exhaust their fuel in around 10 million years compared to 10 billion years for yellow stars like our sun.
Betelgeuse (Arabic for “house of the twins”) is a red supergiant estimated to be 640 light years away. Betelgeuse marks Orion’s right arm or shoulder. The light output from Betelgeuse varies somewhat unpredictably over the course of several years, although Betelgeuse has always remained a 1st-magnitude star. This variability in brightness is common among red giants and supergiants, dying stars which have exhausted most of their core hydrogen and now appear red because their bloated outer layers are cooler than those of blue, white or yellow stars. If Betelgeuse were located in the same position as the Sun, its surface would extend past the orbit of Mars.
The gamma star in Orion is named Bellatrix, a queen of the Amazons in Greek mythology. Bellatrix is a second-magnitude star estimated to be 240 light years from Earth. Bisecting the constellation of Orion is the Belt, made up of three second-magnitude stars named Mintaka, Alnilam and Alnitak. These stars are occasionally called the three kings. Mintaka lies almost exactly on the celestial equator. Directly south of Orion’s Belt is a group of three stars referred to as Orion’s Sword; the middle “star” of the Sword is actually the Orion Nebula, discussed in the next section.
Deep Sky Objects
Orion contains several deep sky objects, the most famous of which are M42 and nearby M43. Together, M42 and M43 comprise the Great Orion Nebula, located approximately 1,400 light years from Earth. To the naked eye, the Orion Nebula appears as a fuzzy star in the middle of Orion’s Sword. A pair of binoculars reveals a blue cloud containing several tiny stars. These stars are sometimes called the Trapezium and are believed to be only a few million years old – extremely young in stellar terms. In a telescope, the Orion Nebula is a truly magnificent site. The other Messier object in Orion is M78, a diffuse reflection nebula located about 1,600 light years away.
To the southeast of Orion’s belt is another famous deep sky object known as the Horsehead Nebula (official designation: International Catalog 434). Unlike the bright Orion Nebula, however, the Horsehead Nebula is a dark dust cloud, which causes it to stand out in stark contrast against its brighter surroundings. The stunning images of the Horsehead Nebula are obtained by the Hubble Space Telescope or long exposure photography; a telescopic view of this object appears far less impressive.
