The Orion Nebula is a famous diffuse emission/reflection nebula located in the constellation Orion. It is also known as Messier 42 (M42) or the Great Orion Nebula. Its designation in the New General Catalogue is NGC 1976. The brightest stars in the nebula form an asterism known as the Trapezium Cluster, and are responsible for most of the nebula’s glow.
The Orion Nebula is one of the brightest nebulae in the night sky and, lying at a distance of 1,344 light years, it is the nearest region of massive star formation to Earth. It can be seen without binoculars, and its brightness and proximity make M42 one of the most studied objects in the night sky.
The nebulous region of M42 is easily seen through binoculars or a small telescope.
The best time of year to observe the nebula is the winter, during the months of December and January, when Orion constellation is high in the sky.
Astronomers studying the nebula have learned a lot about the formation of stars and planetary systems from collapsing dust and gas clouds, and they have observed the effects of massive stars photo-ionizing the clouds in the nebula.
They have also discovered what they believe are some of the younger protostars ever found.
The Orion Nebula spans a degree in the sky, and includes stellar associations, reflection nebulae, dust and gas clouds, and ionized volumes of gas.
FACTS AND LOCATION
The Orion Nebula lies at a distance of 1,344 light years (400 parsecs) from Earth, and can be found in the constellation Orion, to the south of Orion’s Belt, one of the best known asterisms in the night sky.
The nebula is located in the sword of Orion and appears as the middle, slightly fuzzy-looking “star” in the sword to the naked eye. Binoculars and small telescopes reveal a cloudy patch of light.
Orion’s Sword can be found by locating the three stars of Orion’s Belt, and then following the curved line of stars that appear to be hanging from the Hunter’s belt. These stars mark Orion’s Sword, and the Orion Nebula appears as the middle star in the sword when seen without binoculars.
Messier 42 is about 24 light years across and has an estimated mass approximately 2,000 times that of the Sun. It is the brighest part of a huge star-forming region, and the nearest region of massive star formation to Earth. The nebula is believed to contain more than 1,000 young stars, and about 700 stars that are still in various phases of formation.
M42 is part of a much larger nebulous region known as the Orion Molecular Cloud Complex, which extends across the Orion constellation and includes a number of famous deep sky objects, among them Barnard’s Loop, the Flame Nebula, the Horsehead Nebula, Messier 43, and Messier 78.
The Orion Nebula was first discovered by the French astronomer Nicolas-Claude Fabri de Peiresc on November 26, 1610. He observed the nebulous region using a refracting telescope.
In 1619, the Swiss Jesuit astronomer and mathematician Johann Baptist Cysat observed the nebula and compared it to a bright comet discovered in 1618. This was the first published observation of the Orion Nebula. The first published sketch was made by the Dutch astronomer and physicist Christiaan Huygens in 1659.
The nebula is home to a well-known young open star cluster, the Trapezium Cluster.
Charles Messier observed the Orion Nebula on March 4, 1769. He also noted three stars belonging to the Trapezium Cluster. When he published the first edition of his catalogue in 1774, the nebula was listed as the 42nd object. It is still known as Messier 42.
The credit for the first ever instance of astrophotography of the nebula – of any nebula – goes to the American doctor, amateur astronomer and astrophotography pioneer Henry Draper, who photographed Messier 42 using an 11-inch refractor to make a 51-minute exposure of the nebula on September 30, 1880.
The Orion Nebula was first observed by the Hubble Space Telescope in 1993, and has been a frequent target since.
Orion Nebula – Messier 42
Coordinates: 05h35m17.3s (right ascension), -05°23’28” (declination)
Visual magnitude: +4.0
Absolute magnitude: -4.1
Apparent dimensions: 65×60 arc minutes
Radius: 12 light years
Designations: Messier 42 (M42), NGC 1976, LBN 974, Sharpless 281
The Trapezium Cluster is a young open cluster located in the Orion Nebula. The brightest four stars in the cluster form an asterism shaped like a trapezium, a quadrilateral with a pair of parallel sides. In a 5-inch telescope, six stars can be observed in good viewing conditions.
The cluster was formed directly out of the Orion Nebula, within the edge of the Orion Molecular Cloud.
The Trapezium Cluster was discovered by the Italian mathematician, philosopher, astronomer and physicist Galileo Galilei on February 4, 1617. He spotted three of the brightest stars in the cluster, but did not see the nebulosity that surrounds them. The fourth of the main stars was not observed until 1673, and the remaining components were discovered later, totalling eight by 1888, with several of the stars revealed to be binary systems later.
The asterism was named the Trapezium Cluster by the Swiss-American astronomer Robert Julius Trumpler in 1931.
Of the four main stars in the cluster, two can be resolved into binary systems, making a total of six stars. The stars are quite young and still in an early stage of evolution. They have an estimated age of a little more than 100,000 years.
The brightest star in the cluster, Theta-1 Orionis C, has an apparent visual magnitude of 5.13. Both this star and the second brightest star are classified as eclipsing binary systems.
The brightest stars in the cluster are between 15 and 30 times as massive as the Sun and lie within 1.5 light years of each other. They illuminate the surrounding nebulous region.
About half the member stars have evaporating circumstellar disks, which means that planetary systems may soon form in their orbits.
The Trapezium Cluster is suspected to be a component of the Orion Nebula Cluster, a larger association of about 2,000 stars spanning an area approximately 20 light years in diameter.
In 2012, a team of astronomers suggested that the cluster may contain an intermediate black hole, more than 100 times as massive as the Sun, at its centre.