The Orion Nebula is a large, bright nebula roughly 24 light-years across and about 1350 light-years away from the solar system. It is among the brightest nebulae in the galaxy (at least viewed from Earth), so much so that it can be readily seen with the naked eye. Today the nebula is actually known as the "star" in the middle of the sword in the constellation of Orion the Hunter. Like all planetary nebulae, telescopes have produced stunningly beautiful imagery of the Orion Nebula, like this snapshot by the Hubble Telescope.
- Formation and Characteristics -
A nebula is a vast cloud of dust and gas (almost entirely hydrogen and helium) floating through space. Viewed from a distance through a suitably powerful telescope, these clouds typically take on recognizable and stunningly beautiful shapes, making them some of the most distinctive phenomena in the night sky. They are believed to be formed when a star at the end of its lifetime exhausts its hydrogen fuel supply, begins to collapse, and sheds its outer layers, throwing enough enormous amounts of matter into surrounding space. Over long periods of time, the resulting clouds can gradually coalesce into new stars, as is occurring today in the Orion Nebula and in similar locations throughout the Milky Way Galaxy.
In the case of the Orion Nebula, this process is actually going on as part of a much larger phenomenon referred to as the Orion Molecular Cloud Complex, which stretches to include the Barnard's Loop nebula, the Horsehead Nebula and the Flame Nebula, all in the same large region of space. The Orion Nebula is currently undergoing considerable star formation (i.e. it is what is known as a "stellar nursery"), including the formation of a cluster marked by four bright stars and named Trapezium. The Hubble Space Telescope has imaged a number of protoplanetary disks around young stars in the nebula, suggesting that they will one day be host to planetary systems, potentially similar to our own solar system.
Over time, stellar evolution will eventually do away with the beautiful nebula we see today. The dust and gas which creates such a spectacular light show in the night sky will either be absorbed into evolving stars, or blown away, dispersing into the interstellar medium.
- History of Observation -
The Orion Nebula has been known to humanity for a very long time. Surprisingly, early astronomical texts in Europe do not mention the nebula as a notable phenomenon between the times of Ptolemy and Galileo. This was not the case elsewhere in the world; Mayan astronomy, for example, is known to have identified the Orion Nebula as an unusual smear or smudge on the night sky rather than as the telltale prick of light of a star.
In the 17th century, as telescopes and astronomy began to rise to prominence, however, interest in the Orion Nebula in Europe returned. A number of important early astronomers, including Christiaan Huygens and Charles Messier, included the unusual feature on their star charts, and Messier named it "M-42" (the 42nd item) on his influential list of stellar phenomena. (Messier had no way of differentiating nebulae from other notable phenomena, so it appears on the list alongside distant galaxies, star clusters, and so forth.) Today the nebula is studied intensively through advanced telescopes, including from orbit, which has allowed astronomers to begin to piece together our current knowledge of it.