The Orion Nebula contains a very young open cluster , known as the Trapezium due to the asterism of its primary four stars. Two of these can be resolved into their component binary systems on nights with good seeing, giving a total of six stars. The stars of the Trapezium, along with many other stars , are still in their early years. The Trapezium may be a component of the much-larger Orion Nebula Cluster , an association of about 2, stars within a diameter of 20 light years.
Observers have long noted a distinctive greenish tint to the nebula, in addition to regions of red and areas of blue-violet. The blue-violet coloration is the reflected radiation from the massive O-class stars at the core of the nebula. The green hue was a puzzle for astronomers in the early part of the twentieth century because none of the known spectral lines at that time could explain it.
There was some speculation that the lines were caused by a new element, and the name "nebulum" was coined for this mysterious material. With better understanding of atomic physics, however, it was later determined that the green spectra was caused by a low-probability electron transition in doubly- ionized Oxygen , a so-called " forbidden transition". This radiation was all but impossible to reproduce in the laboratory because it depended on the quiescent and nearly collision-free environment found in deep space.
History The Maya of Central America have a folk tale that deals with the Orion constellation's part of the sky. Their traditional hearths include in their middle a smudge of glowing fire that corresponds with the Orion nebula. This is clear pre-telescope evidence that the Maya detected a diffuse area of the sky contrary to the pin points of stars. This nebula is currently visible to the unaided eye, yet oddly there is no mention of the nebulosity in the written astronomical records prior to the seventeenth century.
In particular, neither Ptolemy in the Almagest nor Al Sufi in his Book of Fixed Stars noted this nebula, even though they both listed patches of nebulosity elsewhere in the night sky.
Curiously this nebula was also not mentioned by Galileo, even though he made telescope observations of this part of the Orion constellation in and This has led to some speculation that a flare up of the illuminating stars may have increased the brightness of the nebula. The Orion Nebula is generally credited as being first discovered in by Nicolas-Claude Fabri de Peiresc as noted in Peiresc's own records.
This image is a digital composite of two minute exposures on hypered format Kodak PPF Pro film. The Orion Nebula is a hotbed of star formation. The stars in and near the Trapezium are young — possibly only , years old. Because of its size and mass, Theta1 C produces tremendous amounts of ultraviolet radiation, which causes nearby gas clouds to fluoresce.
Theta1 C is , times brighter than the Sun, and it produces a stellar wind that blows at 5. This tremendous wind blows planet-forming dust particles away from the surrounding stars, making it impossible for planets to form. Conditions within the Orion Nebula are incredible. A perfect storm of cosmic proportions is taking place in M Disks of dust and gas surround small, low-mass stars that produce stellar winds.
This storm will continue as long as the supermassive star continues to produce energy. No matter how much we know about the physical nature of this complex region, the Orion Nebula never fails to delight when seen for the first time or after many years. When first shown Orion, children relate the shape of this constellation to a bow tie, an hourglass, or even a butterfly.
In the latter case, the great nebula marks one of the colorful spots on its wing. When seen through a small telescope, however, it resolves into four stars called the Trapezium. The stars A, B, C, and D received their designations according to their right ascensions, not their brightnesses. Star A shines at magnitude 6. If your sky is steady, an 8-inch scope may reveal 11th-magnitude E and F. You probably will need a inch telescope to find G and H, which both glow faintly at 15th magnitude.
Who saw it first? Scientists give most of the credit to Dutch astronomer Christiaan Huygens — He was also an avid observer. Huygens built and used several long-focal-length refracting telescopes. Near the end of the 18th century, English astronomer William Herschel turned one of his first telescopes on this cosmic wonder. Herschel continued to build bigger telescopes, which culminated with a scope containing a inch mirror.
This instrument gave bright, detailed views of celestial objects but was hard to maneuver. The Orion Nebula was the last object Herschel viewed through this telescope before he retired the ungainly beast. French comet hunter Charles Messier — was the one who really put the Orion Nebula on the map.
In , Messier spotted what would become known as the Crab Nebula. He made it the first entry — M1 — in his now-famous catalog of deep-sky objects.
By , Messier had developed a list of 41 objects he wanted to publish. As always, reality is more complex than it seems at first glance. Greek mythology provides many stories about Orion the Hunter.
One myth says that the gods placed Orion in the sky as a punishment for his arrogance. Another declares Orion was in love with the beautiful goddess Diana.
Another story claims Orion threatened to kill all animal life on Earth. To prevent this, the Earth goddess, Gaia, sent a scorpion that stung Orion on the heel, killing him.
Regretting her actions, Gaia placed Orion opposite Scorpius the Scorpion in the sky so Orion could never be harmed again. Any star chart shows this arrangement. The ancient Egyptians saw Orion as the god Osiris, the husband of Isis. Seth killed his brother Osiris in an ancient rivalry. To make certain the job was complete, Seth chopped Osiris into 14 pieces and scattered them throughout Egypt. Isis recovered all but one part and placed Osiris in the sky as the constellation Orion , where he could be seen by all.
Orion was also identified with Unas, the last Pharaoh of the Fifth Dynasty, who was said to have eaten the flesh of his enemies and devoured the gods themselves to become great and bring inheritance of his power.
According to myth, Unas travels through the sky to become the star Sabu, or Orion. Because pharaohs were believed to be transformed into Osiris after their passing, some of the greatest pyramids — the ones at Giza — were built to mirror the pattern of the stars in the constellation.
Also captured is the red supergiant Betelgeuse top left and the famous belt of Orion composed of the OB stars Alnitak, Alnilam and Mintaka. To the bottom right can be found the star Rigel.
The photograph appeared as the Astronomy Picture of the Day on October 23, In Hungarian mythology, Orion is identified with Nimrod, a famous hunter and father of Hunor and Magor, the two twins also known as Hun ad Hungarian.
The Chinese knew the constellation as Shen, a great hunter or warrior. Another ancient legend dates back to the second millennium BC. The Hittites a Bronze Age people of Anatolia, the region comprising most of present-day Turkey associated the constellation with Aqhat, a famous mythical hunter. The war goddess Anat fell in love with him, but after he refused to lend her his bow, she tried to steal it.
However, the man she sent to get the bow botched the assignment pretty badly, doing away with Aqhat and dropping the bow into the sea. This is why, according to the myth, the constellation drops below the horizon for two months in the spring. Rigel is the brightest star in the constellation.
With an apparent magnitude of 0. Even though it does not have the designation alpha, it is almost always brighter than Betelgeuse , Alpha Orionis. Rigel is really a star system composed of three stars. It has been a known visual binary since , possibly even earlier, when F. Struve first measured it. Rigel is surrounded by a shell of expelled gas.
Rigel is a blue supergiant. It belongs to the spectral type B8lab and is It has 85, times the luminosity of the Sun and 17 solar masses. It is classified as a slightly irregular variable star, with its luminosity varying from 0. The primary component in the system, Rigel A, is times brighter than Rigel B, which is itself a spectroscopic binary star. Rigel B has a magnitude of 6. It consists of a pair of B9V class main sequence stars that orbit a common centre of gravity every 9.
Rigel, Beta Orionis, is associated with several nearby dust clouds which it illuminates. The most famous one is IC , also known as the Witch Head Nebula , a faint reflection nebula located about 2. Rigel is a member of the Taurus-Orion R1 Association. It was considered by some to be an outlying member of the Orion OB1 Association, a group of several dozen hot giants belonging to the spectral types O and B, located in the Orion Molecular Cloud Complex.
However, the star is too close to us to be a real member of that particular stellar association. Rigel is only about 10 million years old. Eventually, it will grow into a red supergiant, one very similar to Betelgeuse. Betelgeuse is the second brightest star in Orion and the eighth brightest star in the sky. It is a red supergiant, belonging to the spectral class M2lab. The suffix -ab indicates that Betelgeuse is classified as an intermediate luminous supergiant, one not as bright as others such as Deneb in the constellation Cygnus.
Some recent findings, however, suggest that the star emits more light than , Suns, which would in fact make it more luminous than most stars in its class, so the classification is likely outdated. The star has an apparent magnitude of 0. Betelgeuse is one of the most luminous stars known. It has an absolute magnitude of Betelgeuse, or Alpha Orionis , is also one of the largest stars known, with an apparent diameter between 0. It is difficult to get an accurate measurement because the star appears to change shape from time to time and, as a result of a huge mass loss, it has a large envelope surrounding it.
Alpha Orionis is classified as a semi-regular variable star. Its apparent magnitude varies from 0. This, however, only happens very rarely. Betelgeuse is believed to be about 10 million years old, which is not much for a red supergiant, but the star is thought to have evolved very rapidly because of its enormous mass. It will likely end its life as a supernova in the next million years. When it does, it will be easy to find in the sky, not just at night, but also in broad daylight.
At its current distance from the solar system, the supernova would shine brighter than the Moon and be the brightest ever recorded supernova in history. The origin of the name Betelgeuse is not entirely certain. Betelgeuse is part of two prominent winter asterisms: the Winter Triangle and the Winter Hexagon. The stars of the Winter Triangle and the Winter Hexagon. The other two stars forming the Winter Triangle , also known as the Great Southern Triangle, are Sirius and Procyon , the brightest stars in the constellations Canis Major and Canis Minor respectively.
Bellatrix , sometimes also known as the Amazon Star, is the third brightest star in Orion and the 27th brightest star in the sky, only slightly dimmer than Castor in Gemini. Bellatrix is a hot, luminous blue-white giant star, classified as an eruptive variable. Its magnitude varies between 1. The star belongs to the spectral class B2 III. It is one of the hotter stars visible to the unaided eye. It emits about 6, times more light than the Sun and has eight or nine solar masses.
Within a few million years, Bellatrix will become an orange giant and eventually a massive white dwarf. Before its own variability was confirmed, Gamma Orionis was used as a standard for stellar luminosity, one against which other stars were compared and checked for variability. Otherwise known as the Belt of Orion, these three blue supergiant stars are hotter and much more massive than the Sun. They lie about 1, light-years away.
Mintaka, Delta Orionis, is the westernmost of the three stars in the Belt of Orion. It is the right-most star when observed from the Northern Hemisphere, facing south. Mintaka is a multiple star, classified as an eclipsing binary variable. The primary component is a double star consisting of a class B giant and a hot class O star which orbit each other every 5. Mintaka is approximately light years distant. Its brightest components are both roughly 90, times as luminous as our Sun and have more than 20 solar masses.
They will both end their lives as supernovae. In the order of brightness, the apparent magnitudes of the components are 2. It is the closest bright star to the celestial equator: it rises and sets almost exactly east and west. Alnilam, Epsilon Orionis, is a hot, bright blue supergiant. It has an apparent magnitude of 1. It belongs to the spectral class B0. It is the fourth brightest star in the Orion constellation and the 30th brightest star in the night sky. It radiates about , solar luminosities.
Alnilam is surrounded by the reflection nebula NGC , a molecular cloud illuminated by the light emitted by the star. It is losing mass and its internal hydrogen fusion is shutting down. Alnilam will soon evolve into a red supergiant, one much brighter than Betelgeuse , and eventually go out as a supernova. Alnitak, Zeta Orionis, is a multiple star system in Orion, approximately light years distant. The brightest component in the system, Alnitak A, is yet another hot, blue supergiant, one with an absolute magnitude of The star has a visual magnitude of 2.
It is the brightest O class star known. It is in fact a close binary star, composed of the O9.
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