Orion: prominent constellation home to massive stellar nurseries

Two of the brightest stars in our sky live here.
Rupendra Brahambhatt
Horsehead and Flame Nebula in the constellation Oriontriphecta/iStock

In 1979, a small ivory tablet dating back to between 32,500 and 38,000 years was discovered in a cave located in the Ach Valley, Germany. The tablet contained a carving that depicts a man-like figure with arms and legs outstretched in the same pose as the stars of the constellation Orion. Some believe that this actually represents the first-star chart, suggesting that humans knew about this vast celestial constellation of stars located on the celestial equator and containing some of the brightest stars in the night sky, around 10 of which are now thought to host exoplanets.

Orion is among the most visible constellations from the Earth, and it is home to some of the brightest stars of our sky such as Rigel and Betelgeuse. 

Orion is the 26th-largest constellation in our sky, it is home to seven main stars and numerous other celestial objects. The distance between Earth and the Orion constellation ranges from 243 to 1360 lightyears away. The closest star to our planet in the constellation is Bellatrix which is around 244 lightyears away, and the farthest star is Alnilam, located at a distance of 1,344 lightyears.

The constellation is named after the huntsman Orion, a character mentioned in Greek mythology, and this is why it is also referred to as the hunter constellation.

Where exactly can you find the Orion constellation?

Orion: prominent constellation home to massive stellar nurseries
The Trapezium inside Orion. Source: C.R. O'Dell and S.K. Wong (Rice University) and NASA/ESA

The Orion constellation is located in the southwestern sky if you are in the Northern Hemisphere or the northwestern sky if you are in the Southern Hemisphere. It is best viewed at latitudes between 85° and -75°.  with the right ascension of five hours and declination of five degrees. It is among the 15-star configurations that intersect the celestial equator. Spread over an area of about 594 square degrees, Orion is bordered by the constellations of Monoceros, Taurus, Lepus, Gemini, and Eridanus.

Belgian astronomer Eugène Joseph Delporte defined the boundaries of Orion, along with the other constellations, in 1930. The Orion constellation can be easily seen during the daytime between May and July, whereas the months between November and February are best for observing the constellation during the nights.

Messier objects in the Orion constellation

Orion: prominent constellation home to massive stellar nurseries
Messier 78. Source: Igor Chekalin/ESO

When French astronomer Charles Messier started looking for comets in the late 1700s, he came across various other celestial objects. The repeated occurrence of such objects was acting as a distraction for Messier in his search for comets. So in 1764, he started to keep a catalog of these objects, later helped by his friend and colleague Pierre François Méchain, in order to avoid mistaking them for comets. 

His initial catalog consisted of 41 entries, and his final catalog, published in 1781, contained 103 entries, along with notes on several other objects he had found. These objects were later named collectively as Messier objects. The Orion constellation also contains three such objects that go by the names Messier 78 (a reflection nebula), Messier 43 (De Mairan's Nebula), and Messier 42 (the Orion Nebula).   

Messier 78

In 1780, Pierre Méchain detected the presence of a reflection nebula in the Orion that spanned across a diameter of 10 lightyears. This vast nebula is around 1600 lightyears away from Earth, and it is home to a number of T Tauri-type stars that are believed to have formed within the last 10 million years. Although fairly bright, they are not yet hot enough for nuclear fusion reactions to having begun in their cores. It will take tens of millions of years more for them to reach full “starhood".

Messier 42

Also known as the Orion nebula, Messier 42 (M42) is located at a distance of around 1344 lightyears from the Earth, and it is also the nearest star-forming region to our planet. It is part of a much larger nebula that is known as the Orion Molecular Cloud Complex. Near the center of M42, is a young star cluster dominated by a group of four giant stars called the Trapezium because they appear in a trapezoid pattern. Ultraviolet light unleashed by these stars may be disrupting the growth of hundreds of smaller stars nearby.

With a magnitude of 5.13, the Trapezium’s Theta-1 Orionis C is the most massive member of the Trapezium. The surface temperature of Orionis C is estimated at around 44,726.85°C (45,000 Kelvin) which is more than seven times that of the Sun. 

Messier 43

Messier 43, or De Mairan's Nebula, is separated from the Orion Nebula by a dense lane of cosmic dust. The nebula was revealed as distinct from the Orion Nebula by French astronomer Jean-Jacques d'Ortous de Mairan, in 1731. The Nebula is shaped by just one star.

Both nebulas are part of the Orion Molecular Cloud Complex, a huge stellar nursery that also includes the Horsehead Nebula (Barnard 33) and the Flame Nebula (NGC 2024). 

The distance between M43 and Earth is approximately 1,600 lightyears, and according to NASA, January is the best time to view this Messier object.

Interesting facts about the Orion constellation

Orion: prominent constellation home to massive stellar nurseries
Source: Guillermo Ferla/Unsplash

Here are some exciting facts that further illustrates the significance of the star-studded Orion constellation:

  • Interestingly, the air shafts of two large pyramids located in Mexico, which are believed to be built in the second century BC, and three pyramids in the Giza plateau may be pointing towards the stars located in the Orion belt. The ancient Egyptians associated the stars of Orion with Osiris, the god of rebirth and afterlife, and believed that the gods descended from the three stars of Orion’s Belt.
  • So far, the International Astronomical Union has assigned names to 10 stars in the Orion constellation. Nine stars of these are either blue, yellow, or bluish yellow stars, but the star named Betelgeuse is a highly luminous red giant. It looks so different from the rest of the Orion stars that you can spot the difference between them even with the naked eye. Betelgeuse is also ranked as the tenth brightest star in our sky. It is more or less tied for brightness with Achernar, but because Betelgeuse is a variable whose magnitude can drop, it is usually given tenth place
  • Though Orion is named after a Greek hunter, the constellation is mentioned in several other cultures as well and goes by a number of different names. For instance, the Norse people called the belt Friggerock (Frigg’s distaff) – A distaff was part of a spinning wheel, and the name refers to the spinning wheel belonging to the goddess Frigga, and what we see as a sword hanging from the belt, they saw as the spindle. The ancient Indian Vedas described Orion as a depiction of Lord Shiva, while the Lakota people called the constellation Tayamnicankhu, and saw it as the spine of a bison. In Spanish tradition, the three stars that form the Orion belt (Alnilam, Mintaka, and Alnitak) were referred to as “Las tres Marías” ((The Three Marys).
  • The Orion constellation is also linked to the annual Orionids meteor shower that takes place every year in October. The shower is caused by the debris produced when Earth crosses the orbit of Halley’s comet. The radiant point for the Orionids is in the direction of the Orion constellation, hence the name Orionids.
  • Beta Orionis, or Rigel, is currently the seventh brightest star visible in the sky, and the brightest naked-eye star in the Orion constellation. It is a blue supergiant located about 864 lightyears from our solar system. It is also called Rigel and is thought to be anywhere from 61,500 to 363,000 times as luminous as our Sun. 

Orion may well be the oldest constellation to be recognized, and it holds various unheard mysteries within. Let us hope that with time, more and more of its valuable secrets will be revealed and help us increase our understanding of the cosmos. 

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