The Constellation of Orion is named after Orion the hunter from Greek mythology, although it is recognized by cultures all over the world and, therefore, many myths and legends are associated with it.
The constellation is home to many interesting stars and asterisms. Around 10 of these stars have been discovered to host exoplanets and there are three Messier objects located in Orion. The brightest star in Orion is Rigel, which is the seventh-brightest star in the night sky.
Orion also has famous nebulae and deep-sky objects, which we will go into more detail about later on. Orion belongs to the Orion family constellations, along with Canis Major, Canis Minor, Lepus and Monoceros.
History and Mythology of the Orion Constellation
One of the earliest depictions of Orion is a prehistoric mammoth ivory carving found in a cave in the Ach valley in West Germany in 1979. It is thought that this carving is between 32,000 to 38,000 years old. Orion can also be found in records in the ancient Babylonian star catalogs of the Late Bronze Age.
In the Ancient Near East, Orion was originally called MULSIPA.ZI.AN.NA, which means the Heavenly Shepherd or the True Shepherd of Anu. Anu was the chief god of the heavenly realms.
In ancient Egypt, Orion’s stars were thought to be a god, called Sah. Orion rises before Sirius, which is the brightest star in the night sky, so Sah was closely related to Sophet, who was the goddess who personified Sirius. In Egyptian mythology, it is also thought that the gods descended from Sirius and the Orion’s Belt asterism, which instigated the human race.
The Pyramid Connection
The pyramids of Giza Plateau mimic the alignment of the three stars that form Orion’s Belt, with the air shafts inside these pyramids pointing directly to the constellation. However, there are also two pyramids in Mexico that have been discovered to also point directly towards Orion’s Belt. These were built in the 2nd century B.C.
In Greek mythology, Orion was a strong hunter that was born to Euryale and Poseidon. One of the most well known myths is when Titan Gaia told Orion, in a fit of rage, say that he would kill every animal on Earth. Titan Gaia tried to get rid of Orion with a scorpion, which is believed to be the reason why the constellations of Orion and Scorpius are never in the sky at the same time.
The scorpion bit Orion, but Ophiuchus, the Serpent Bearer, revived him. This is believed to the reason why the constellation of Ophiuchus stands midway between Scorpius and Orion in the sky.
Location of the Orion Constellation
As we have mentioned above, the Orion constellation is the 26th largest constellation in the sky, stretching for around 594 square degrees. It is one of the brightest constellations and is therefore very easy to spot. It can also be seen all over the world, because it lies on the celestial equator.
Its right ascension is 5 hours and is declination is +5 degrees. It is visible between +85 degrees and -75 degrees and is best viewed at 9pm, during January.
The neighboring constellations to Orion are Eridanus, Gemini, Lepus, Monoceros and Taurus. Due to the fact that Orion is closely associated with Greek mythology and is known as the hunter, Orion is often depicted in star maps as facing Taurus (zodiacal constellation), who, with his two hunting dogs (Canis Major and Canis Minor), is pursuing the Pleiades sisters (represented by an open cluster) or chasing after the hare (constellation Lepus).
There are three Messier objects in the constellation of Orion. Two of them, Messier 42 and Messier 43 are nebulas and Messier 78 is a reflection nebula.
Messier 42, also known as NGC 1976 and the Orion Nebula, is located south of the Orion’s Belt asterism and is a diffuse reflection nebula. It is 1,344 light years away from Earth and is one of the brightest nebulae in the sky. With a visual magnitude of 4.0, it can be seen without binoculars.
The naked eye makes Messier 42 appear as a slightly blurred “star” in the center of Orion’s Sword asterism. It is the nearest known region of massive star formation to the Solar System and is part of the Orion Molecular Cloud Cluster.
Located in the Orion Nebula is the Trapezium or Orion Trapezium Cluster. This is a very young open cluster which is recognized by its four brightest stars that form a trapezium-shaped asterism.
The brightest star in the Orion Trapezium Cluster is Theta-1 Orionis C. It is a blue main-sequence star of spectral class O6pe V and has an apparent magnitude of 5.13. It is located 1,500 light years away from Earth and is one of the most luminous stars with a surface temperature of 45,000 K — around 7.7 times hotter than our Sun.
Messier 43, also known as NGC 1982 and De Mairan’s Nebula, is a star-forming emission-reflection nebula. It actually part of Orion Nebula, but is separated from it by a large lane of interstellar dust.
Messier 43 has an apparent magnitude of 9.0 and is located 1,600 light years away from us. It is also located at around seven arcminutes north of the Trapezium cluster.
Messier 78, also known as NGC 2068, is a reflection nebula that surrounds two 10th magnitude stars and can be easily be found in a small telescope. It contains around 45 T-Tauri type variable stars, which are young stars still in the process of formation.
Messier 78 is 1,350 light years away from us and has an apparent magnitude of 8.3 and a radius of 5 light years.
Orion is home to many bright stars, some of which are the brightest stars in the night sky. The brightest star in Orion is Rigel, which is closely followed by Betelgeuse.
Rigel, also known as Beta Orionis, is the seventh-brightest star in the night sky and is a massive blue-white supergiant variable star. It appears as a single star, but is actually a star system that contains four stars.
The primary star, Rigel, is an Alpha Cygni variable star. It is around 61,500 and up to 363,000 times brighter than our Sun and has an apparent magnitude ranging from 0.05 to 0.18.
Rigel is located around 860 light years away from Earth and has a 7,000% of our Sun’s radius and 2,100 % of its mass. As years go on, Rigel will expand to an even greater size and transcend into a red supergiant, possibly exploding into a Supernova one day.
Rigel is occasionally outshone by Betelgeuse, although it is the brightest star in Orion. Alongside Betelgeuse, Bellatrix and Alnilam, Rigel makes up the navigational stars of the Orion constellation.
Betelgeuse, also known as Alpha Orionis, is the second brightest star in Orion and occasionally outshines Rigel. It has an apparent magnitude of +0.0 and +1.13, which varies because it is a red supergiant semi-regular variable star. It is the ninth brightest star in the night sky and has the widest range of varying magnitude out of any first-magnitude star.
Betelgeuse’s brightness ranges from 90,000 to 150,000 times that of our Sun and has a radius of around 88.700% of our Sun’s radius and 1,160% of its mass. It is located at around 640 light years away from Earth. Betegeuse is cooler than our Sun thanks to it’s size, with a temperature of around 3,500 K.
It is surrounded by an intricate envelope that is around 250 times its size. The envelope is made up of its lost mass, as Betelgeuse loses around 1 solar mass every 10,000 years.
Bellatrix, also known as Gamma Orionis, is the third brightest star in Orion and varies in being the 27th and the 25th brightest star in the night sky. It has an apparent magnitude of 1.59 and 1.64, being a slightly variable star.
It is a blue star located at around 250 light years away from Earth and is around 9.211 times brighter than our Sun. Bellatrix also has around 575% of our Sun’s radius and around 860% of our Sun’s mass.
Mintaka, also known as Delta Orionis, is the seventh brightest star in Orion and the 73rd brightest star in the night sky. Along with Alnilam and Alnitak, it is one of the famous three belt stars that form Orion’s Belt. It is the smallest and least massive star in Orion’s Belt.
Located 1,200 light years away from us, Mintaka is a multiple star system and it’s primary component, Mintaka A, is a blue giant star that is around 190,000 times brighter than our Sun. It is 5.1 times hotter than our Sun, with a temperature of 29,500 K and around 20 times bigger than our Sun. It has around 24 solar masses and a radius of about 16.5 times that of our Sun.
Alnilam, also known as Epsilon Orionis, is one of the three stars that form Orion’s Belt. It is the 4th brightest star in Orion, and the 29th brightest star in the night sky. It is a bright blue supergiant star and the biggest and most massive star of the Belt, situated in the middle. Alnilam is also an Alpha Cygni variable star with a brightness that varies from magnitude 1.64 to -1.74.
Alnilam is located around 1,975 light years away from us and is around 537,000 times brighter than our Sun. It is also more than 30 times bigger and has around 4.000% of its mass. It illuminates a molecular cloud that surrounds it, NGC 1990.
Alnitak, also known as Zeta Orionis, is another of the three stars that form Orion’s Belt. It is a triple star system with the primary star, Alnitak, being the 5th brightest star in Orion, and the 31st brightest star in the night sky.
Alnitak is a blue supergiant star with an apparent magnitude of 2.0. It is located 1,260 light years away from us and is 250,000 times brighter than our Sun. Alnitak has 33 solar masses, and a radius of around 20 times that of the Sun.
It is the second most massive and the second-biggest star in Orion’s Belt. Alnitak is also a fast-spinning star, having a rotational velocity of around 110 km/68 mi per second.
Saiph, also known as Kappa Orionis, is the sixth brightest star in Orion and a supergiant star with a slightly variable star of magnitude 2.09, varying by about 0.4 magnitudes. It is one of the four stars that comprise Orion’s main quadrangle and is a supernova candidate that will explode in the near future.
Saiph is located at around 650 light years away from Earth. It is 56,881 times brighter than our Sun, has 15.50 times its mass and 22.2 times its radius. It is hotter than Rigel, with a surface temperature of around 26,500 K.
Meissa, also known as Lambda Orionis, is the eighth brightest in Orion and is a multiple star system. It is located around 1,100 light years away from us and has an apparent magnitude of 3.33. Its primary star, Meissa, is a giant star which is 165,000 times brighter than our Sun. It also has 27.9 times its mass and 10.0 times its radius.
Meissa is also the dominant member of the Collinder 69 cluster, which is a 5-million-year-old-star forming region. The ultraviolet energy radiating from Meissa is creating the Sh2-264 H II region in the neighboring volume of space.
Asterisms In The Orion Constellation
There are five famous asterisms of Orion — Belt, Sword, Head, Club and Shield. As we have mentioned above, the stars making up the Belt are Mintaka, Alnilam and Alnitak.
The Orion’s Sword asterism contains the Orion Nebula, which is also known as Messier 43 nebula, as well as the Running Man Nebula and the stars Theta Orionis, Iota Orionis and 42 Orionis.
The Orion’s Head asterism is made up of three stars — Meissa — Lambda Orionis — and Phi-1 and Phi-2.
The Orion’s Club asterism is north from Betelgeuse, made up of Mu Orionis, Nu, Xi, Chi1 and Chi2. East of Chi1 is the Mira-type variable red giant star – U Orionis.
Orion’s Shield is made up of six stars, all of which are situated west from Bellatrix. They are known as Pi Orionis — Pi1, P2, P3, P4, P5 and P6.
Deep Sky Objects
The most common deep sky objects of Orion are the nebulae. There are also clusters and meteor showers that are well known.
We have mentioned the Messier nebulae above, but here are some of the other well known nebulae.
The Horsehead Nebula, also known as Barnard 33, is a dark nebula located south of Alnitak, in the bright emission nebula IC 434. It is also located around 1,375 light years away from us and is part of the Orion Molecular Cloud Complex.
The Horsehead Nebula was first discovered in 1888 by Williamina Fleming. It received it’s name thanks to the the shape of its dark dust clouds and gases which resembled the head of a horse.
Barnard’s Loop is an emission nebula and is also part of the Orion Molecular Cloud Complex. It has an apparent magnitude of 5 and is around 150 light-years in radius, covering much of the constellation of Orion. It appears as a large arc centered on Messier 42 and is around 1,600 light years away from Earth.
Many think that the Barnard’s Loop nebula was formed in a supernova explosion around 2 million years ago. It is named after E.E. Barnard, who was the astrophotographer who photographed the nebula and published a description in 1894.
The Flame Nebula
The Flame Nebula is also an emission nebula and is located around 1,300 light years away from Earth. It is part of the Orion Molecular Cloud Complex and is is illuminated by the hot blue supergiant Alnitak. It has a magnitude of 2.0.
The Flame Nebula is very interesting to look at. Alnitak emits ultraviolet light into the nebula, knocking electrons from the hydrogen gas clouds inside the nebula. The glow of the nebula is the result of the electrons and ionized hydrogen recombining.
NGC 2023 is a reflection nebula that is lit by the B star HD 37903. It is among the brightest sources of fluorescent molecular hydrogen and is among the largest reflection nebulae in the sky. NGC 2023 can be found a third of a degree from the Horsehead Nebula. It is 4 light years in diameter and is located around 1,467 light years away from Earth.
Monkey Head Nebula
Monkey Head Nebula, also known as NGC 2174, is an emission nebula classified as an H II region. It is believed to have formed through hierarchical collapse, which is when dense regions within molecular clouds collapse and form stars.
The Monkey Head Nebula is located around 6,400 light years away from us and has an apparent magnitude of 6.8. It is also associated with the open cluster NGC 2175 which is also located in Orion.
The 37 Cluster – NGC 2169
NGC 2169 is an open star cluster that has an apparent magnitude of 5.9. It is located around 3,600 light years away and consists of around 30 young stars, which are around eight million years old. It is just under seven arc minutes in diameter and is called the 37 cluster since it resembles the number 37.
Orion Trapezium Cluster
The Orion Trapezium Cluster is a young, tight, open cluster situated in the middle of the Orion Nebula. It was first discovered by Galileo Galilei in 1617 and is 47 arcseconds in size with an apparent magnitude of 4.0.
The brightest star in the Orion Trapezium Cluster is Theta-1 C Orionis, which is a blue main-sequence star of spectral class O6pe V. It has an apparent magnitude of 5.13, and it is around 1,500 light years away from us. Just five of the brightest stars in the Trapezium emit most of the light that illuminates the surrounding nebula.
Orion Molecular Cloud Complex
The Orion Molecular Cloud Complex, also known as Orion Complex, is between 1,500 and 1,600 light years away from us and can be seen with the naked eye. It is compromised of large group of dark clouds, emission nebulae, reflection nebulae, H II regions and young stars.
The Orion Complex is also home to the majority of the well-known deep sky objects in Orion, such as Messier 43, Messier 78, Barnard’s Loop, the Flame Nebula, the Horsehead Nebula and Orion Nebula.
The Orionid meteor shower reaches its peak at around 20 October each year. There are around 20 meteors per hour during this time. It’s radiant appears to be the constellation of Orion and the shower’s parent body appears to be Halley’s Comet.
Orion is often used as a navigation aid to help find other stars. Rigel, Betelgeuse, Bellatrix and Alnilam are used at the navigational stars of the Orion constellation because of their brightness and simplicity to recognize.
An extended imaginary line from Orion’s Belt asterism southeastwards points towards Sirius, the brightest star in the sky. The star Aldebaran can be found northwestward and is the brightest star in the constellation of Taurus.
An imaginary line extended from Rigel through Betelgeuse points towards Castor and Pollux, which are the brightest stars of the Gemini constellation. Rigel is also part of the Winter Circle asterism and Betelgeuse is part of the Winter Triangle asterism, which both mark the center of the Winer Hexagon.
An imaginary line that is drawn eastward across the two shoulders of Orion, marked by Bellatrix and Betelgeuse, shows the direction of Procyon. This is the brightest star in the constellation of Canis Minor.
Due to the effects of the Earth’s axis, the Orion constellation will not always lie on the celestial equator. Orion currently lies south of the ecliptic, but as time goes on, Orion will be moved further south. It is thought that by AD 14,000, Orion will be so far south that it will become invisible from the latitude of Great Britain.
Extra Facts On The Orion Constellation
- In China, Orion is seen as one of the 28 lunar mansions and is known as Shen.
- In India, the cosmic dancer Nataraja is seen in the Orion constellation.
- Orion’s belt is known as Frigg’s Distaff in Scandinavian tradition.
- In Hungarian tradition, Orion is known as the “magic Archer” and is called Nimrod
- In Aramea, the Nephilim, the offspring of the “sons of God”, were said to be Orion’s descendants.
- Orion was known as al-Jabbar, “the giant”, in medieval Muslim astronomy.
- In Finland, Orion’s belt and the stars below it are known as Väinämöisen viikate.
- The Seri people of northwestern Mexico call the three stars in the belt of Orion Hapj (a name denoting a hunter) which consists of three stars: Hap (mule deer), Haamoja (pronghorn), and Mojet (bighorn sheep).
- The seven primary stars of Orion make up the Polynesian constellation Heiheionakeiki which represents a child’s string figure similar to a cat’s cradle.
Some Images created with the NightVision app – https://www.nvastro.com/nvj.html
Some Images created with the Stelvision Sky Map https://www.stelvision.com/en/sky-map/
Orion 1 – https://astrobackyard.com/orion-constellation/
Orion 2 – https://www.space.com/23966-orion-constellation-weekend-stargazing.html
Messier 42 – https://en.wikipedia.org/wiki/Orion_Nebula
Orion 3 – https://www.spacetelescope.org/images/opo0205b/
Orion 4 – https://starregistration.net/constellations/orion-constellation.html
Messier 43 – https://en.wikipedia.org/wiki/Messier_43
Rigel – https://earthsky.org/brightest-stars/blue-white-rigel-is-orions-brightest-star
Betelgeuse – https://www.sciencefocus.com/news/is-the-betelgeuse-star-about-to-explode/
Bellatrix – http://www.astronomytrek.com/star-facts-bellatrix/
Mintaka – https://en.wikipedia.org/wiki/Mintaka
Horsehead Nebula – https://en.wikipedia.org/wiki/Horsehead_Nebula
The Flame Nebula – http://annesastronomynews.com/photo-gallery-ii/nebulae-clouds/the-flame-nebula/