Most people mistake the Orion Nebula for a star in the constellation of Orion, but it is actually the most easily detectable naked-eye nebula in the entire night sky. This magnificent star-forming region is also a hugely popular deep-sky target for stargazers to explore. So, read on and find out what exactly is the Orion Nebula, where M42 is located, and lots more interesting Orion Nebula facts besides.
1: Quick Facts
Constellation: Orion
Distance: 1,300 light years
Type: Emission/Reflection Nebula
Span: 25 light years
Apparent Magnitude: +4.0
Discovery Date: 1610
The Orion Nebula, also known as M42 (Messier Object 42) or NGC 1976 (New Galactic Catalogue object 1976), was discovered in 1610 by French astronomer Peiresc Nicolas-Claude Fabri de Peiresc using the newly invented refracting telescope.
2: Located in Southern Sky
The Orion Nebula is visible, even in moderate light-pollution, and finding it is relatively easy as it is located within one of the night sky’s most prominent constellations, after which the nebula is named. Straddling the celestial equator also means that the constellation of Orion is visible from most places on the planet, or at least those located between latitudes +85° and -75°. In the Southern Hemisphere, however, the Orion constellation appears upside down, with the giant standing on his head. Interestingly, the celestial equator passes roughly through the top right star in Orion’s belt, meaning that the Orion Nebula’s location is officially in the southern celestial sphere.
3: Observed During November to April
Orion can be seen from November to April, which in the Northern Hemisphere is late autumn to early spring, and in the Southern Hemisphere is summer and autumn. Nearly everyone can recognise the three aligned stars of Orion’s belt, even if they don’t know their names (Almitak, Alnilam, and Mintaka), and hanging from this asterism is Orion’s Sword, which seems to be composed of three stars, namely 45 Orionis, Theta Orionis and Iota Orionis. The middle one, however, is where the Orion Nebula (M42) is found, with the region being illuminated by a multiple star system at its centre known as “The Trapezium”.
4: Part of Orion Molecular Cloud Complex
The Orion Molecular Cloud Complex is a vast cloud of gas and dust located within the Milky Way galaxy that contains a number of different nebulae, including the Orion Nebula (M42), the neighboring De Mairan’s Nebula (M43), the Flame Nebula (NGC 2024), the Horsehead Nebula, the Running Man Nebula, and Barnard’s Loop. This giant molecular cloud is around 240 light-years wide, 1,600 light years distant, and spans almost the entire constellation, as can be seen in the image at the top of this article. Several parts of it are also visible to the naked eye, including the part we call the Orion Nebula, which occupies just 25 light-years of the Orion Molecular Cloud, on the side facing Earth.
5: Both Reflection and Emission Nebula
The Orion Nebula is mostly composed of hydrogen, but contains some helium, carbon, nitrogen, and oxygen. It also has the distinction of being both a reflection and emission nebula, meaning that it is illuminated by the light from nearby stars, as well as being energized by radiation from stars produced within the nebula, which then heats the nebula’s surrounding gas causing it to fluoresce and glow. In fact, there are eight star clusters associated with the Orion Nebula, the brightest of which is mostly responsible for illuminating the whole of its surroundings, namely the Trapezium cluster.
6: Contains Trapezium Cluster
Near the centre of the Orion Nebula is Trapezium, which is a one million years old open cluster, making it one of youngest star clusters ever discovered. The main component of this group is the star Theta1 Orionis, which is multiple system famous for its four bright members (A, B, C, and D), which form a trapezoid shape, and were created from matter contained within the Orion Nebula. They are spaced within just 1.5 light years of each other, and together with a few fainter stars, shine with a combined visual magnitude of +4. There are, however, around one thousand stars located within the Trapezium Cluster, which occupies an area around four light-years across, or roughly the distance between the Sun and the Alpha Centauri star system.
7: Both Stellar and Planetary Formation
The Orion Nebula is actually a stellar nursery composed of gas and dust in the process of condensing into stars and planets. In fact, this is where we have learned most of what we know about star and planetary formation, and the information we accept as “obvious” about the evolution of stars was, in large part, gleaned from this source. According to some estimates, M42 contains more than 1,000 stars, with the very youngest ranging from 10,000 to 300,000 years old, and by observing them scientist have had the opportunity to study the initial formation of protoplanetary disks around some of these stars, which signal the very beginnings of solar system formation.
8: Contains an Interstellar Bow Shock
One particularly stellar object of interest is the young variable star LL Orionis, which is adrift in the Orion Nebula and forging its way through the stellar dust. Much like a ship creates waves at its front end (bow) as it moves through the water, so too does LL Orionis create a spectacular bow wave as the fast-moving stellar wind of hot gas and charged particles it produces pushes the nebula’s slow-moving cooler gas and dust aside. The size of the LL Orionis Bow Shock is around 0.5 light years across, while the star itself has around 2 solar masses, and a flow speed of between 45,000 and 180,000 mph.
9: Deep-Sky Observers Favorite
The Great Orion Nebula is one of the most popular stellar targets for amateur astronomers because of its constant evolution, and the new things you can observe every time you look at it. Therefore, you should not miss the opportunity to view the Orion Nebula through a telescope or other optical equipment. With the naked eye, for instance, M42 appears as a fuzzy patch of faint light, while 10×50 binoculars will reveal a larger, brighter image, with wings of nebulosity stretching out from its central region, and two prominent stars of the Trapezium easily visible. A 3.1-inch (80mm) telescope, on the other hand, will yield a view of the Trapezium’s four main components, while more of the stars in this group will need a 6-inch (150mm) telescope to resolve.
While the images of M42 we are used to seeing in photos reveal stunning hues of red, brown and green, seeing color is a trickier proposition as our eyes are poor at discerning color at low light levels. The human eye is much more sensitive to green light, however, and observers are more likely to see the green color emitted by oxygen ions, although some stargazers using even a small 6 inch scope have reported seeing hints of the red produced by ionized hydrogen gas.
10: Surrounded by Myriad of other Deep-Sky Objects
Surrounding M42 in Orion’s Sword is a myriad of other deep-sky objects to explore, including just south of M42 the blue-white star Iota Orionis, the brightest star in Orion’s sword, which is a triple star system that is embedded inside a nebula called NGC 1980. To the east of M42 can be found De Mairan’s Nebula (M43), which is actually part of the Orion Nebula despite having been given a unique Messier designation. Meanwhile, M42 and M43 are separated by a dark nebula region called the Fish Mouth that appears to be biting into the Trapezium cluster.
Exploring further, located at the northernmost part of Orion’s Sword is a collection of reflection nebulae (NGC 1973, NGC 1975 and NGC 1977) which are collectively called The Running Man Nebula, while further north still is a loose cluster of around 20 stars called NGC 1981. Of course, there are plenty of other fascinating objects to be seen in the area surrounding the Great Orion Nebula, making it a particularly rich target for stargazers, particularly in the wintertime when the air is cold and steady. While there is plenty to look at, though, M42 continues to be regarded as one of the night sky’s main attractions for deep sky observers.