Nebulae, named for their diffuse shape, are vast regions in space filled with interstellar material: dust and gas. The Orion Nebula was first described by French astronomer Nicolas-Claude Fabri de Peiresc in 1610, although ancient civilizations such as the Maya, for example, have records of similar objects. However, it is not possible to guarantee that it was actually the same nebula as Orion.
In fact, Galileo does not mention it, although it is known that he examined the region with his telescope and detected some stars within it (known as the Trapezium ). Nor are other notable astronomers of antiquity.
But since it can now be seen easily with the naked eye, the nebula may have increased in brightness due to the birth of new stars.
Charles Messier cataloged it in 1771 as the M42 object, a name by which it can also be searched on the web and in astronomy apps for phones.
From an astronomical point of view, nebulae such as Orion’s are important, as the stars continually form there.
Due to the force of gravity, this is where the aggregates of matter appear that later condense and constitute the seed of star systems. Inside the nebula, stars are continually forming.
The Great Orion Nebula is relatively close to the solar system, 500 parsec (1 parsec = 3.2616 light years) or 1270 light years. As we said, it is located in the belt of Orion, composed of the three bright stars diagonally in the center of the quadrilateral of the constellation.
These three stars are Mintaka, Alnilam and Alnitak, although they are colloquially called the Three Marys or Three Kings.
From Earth, the angular diameter (the size of the angle at which the object is seen from Earth) of the nebula in the sky is approximately 60 minutes of arc.
For comparison, Venus, an easily visible celestial body, ranges from 10 to 63 minutes of arc, depending on the weather, but Venus’ appearance is brighter for proximity reasons.
You can get an idea of the size of the nebula and its true brightness by comparing the distances: 1270 light years = 1.2 x 10 16 km, against a Venus-Earth distance of just 40 x 10 6 km.
How to observe the Orion Nebula?
The Orion Nebula is an emission nebula, meaning it emits light in the visible range. It is visible in the east, towards dawn from the month of July, but the best time to observe is during the northern hemisphere winter months or the southern hemisphere summer.
It is visible to the naked eye if the sky is dark and clear. And while it’s true that it might be visible from a big city, it’s best to stay as far away from light pollution as possible.
Through binoculars or a small telescope, the nebula looks like a small pearly dot, although a slight pink is sometimes seen. This is not the most common, because the eye is not as sensitive to color as photographic film.
Therefore, the viewer will not see it as in the photo shown in Figure 1. This requires larger telescopes or taking long exposure photographs, which often also undergo additional processing to bring out details.
Despite this, even if seen only through binoculars, the nebula is an image of startling beauty, all the more so knowing that the stars are rising within it now.
Finding the nebula is easy, as has been said, as Orion is one of the best known constellations. Likewise, an app like Sky Map will show your location immediately. And with modern telescopes, you can program the search to focus automatically and locate the trapezoid inside.
At the center of the Orion Nebula are four stars known as The Trapeze ( Θ-Orionis). Galileo discovered three of them in 1610, but curiously, he did not leave a record of the cloudiness that surrounded them, which Fabri de Peiresc did.
The stars that make up the trapeze are bluish white and very bright. They are also huge, between 15 and 30 times the mass of the sun.
They are relatively close: 1.5 light-years apart each separates approximately. They are part of a much larger stellar cluster , about 10 light-years across and about 2,000 stars, called the trapezoid cluster .
The trapeze can be observed with the help of a small telescope and, in very clear skies, an additional fifth star is distinguished. Larger telescopes can distinguish up to 8 stars.
The color of the Orion Nebula
To the naked eye, the nebula is whitish, although sometimes, under the right conditions, the human eye is able to detect a slight pinkish tint.
True colors are seen in images captured over long exposures and come from the energy emitted by excited gas molecules.
In fact, the stars inside the nebula have temperatures around 25,000 K. Therefore, they are able to emit enough ultraviolet radiation to ionize hydrogen, which is the major component in the region.
The combination of wavelengths emitted by the molecular excitation of the gas (in red, blue and violet) produces the distinct pink color.
In some photographs, green areas were also observed, corresponding to different energy transitions that only occur in places with the physical conditions of the nebula.
Resources and data
Due to the great stellar activity inland, the Orion Nebula is of great astronomical interest. Inside, there are a large number of stars forming, called protostars.
Since this is a very brief stage in a star’s life, it’s not easy to find protostars to study. And since the great Orion nebula is far from the plane of the galaxy, what it contains is not easily confused with other objects.
For all these reasons, astronomers and astrophysicists have studied it extensively.
Facts about the Orion Nebula
-The age of the nebula is estimated to be less than 2 million years, which is the same age as the stars of the clusters that form it.
-Hydrogen is the most abundant element in the nebula and therefore we see it as reddish or pink because the red light from the hydrogen emission lines is the most intense.
-Stars are surrounded by bright filaments that extend to distances of 8 parsecs. Some of these filaments are meeting fronts between particles that move slowly with others that move more slowly.
-In the interior of the nebula, stars with protoplanetary disks and brown dwarfs, among other objects, were detected.
The proplyds are composed of material which is around newly formed stars , and gives rise to planetary systems as ours.
About 85% of the stars in the nebula are surrounded by disks of gas and dust, although that doesn’t necessarily mean they develop a planetary system like ours.
Brown dwarfs , on the other hand, are bodies halfway between stars and planets, because they didn’t have enough mass to create the fusion reactor that gives rise to a star.
Given the high stellar birth rate, there are numerous brown dwarfs in the great Orion nebula.
-The Orion Nebula is a visible part of the large Orion Molecular Cloud or Orion Molecular Complex, which groups different types of nebulae and other astronomical objects, such as the Barnard loop (in the shape of a horn in the image below) and the known dark horse head nebula.
The Orion nebula is gradually dispersing and is expected to be extinguished in a few hundred thousand years, a blink of an eye from the universe’s point of view. There is still time to enjoy such a spectacular celestial phenomenon.
The following diagram shows the structure of the Great Orion Nebula and adjacent regions.
Using infrared shots, the structure is much better distinguished as gas and dust are transparent at these wavelengths, while visible light is fully dispersed or absorbed.
The trapeze stars, already described, have been shifted to the left in the image.
Within the nebula, the outer molecular cloud is also distinguished and, within it, the following objects, visible in the infrared:
-The Becklin-Neugebauer object, visible in the infrared, is an intermediate-mass protostar, that is, a star at a very early stage that has not yet been incorporated into the main sequence.
– Masers or natural sources of microwave emission are typical formations of molecular clouds.
-The Kleinmann-Low Nebula, a very active star-forming region in the heart of the Orion nebula. It contains a star cluster surrounded by dust and gas that also includes protoplanetary disks.