[7] The Orion Nebula is one of the most scrutinized and photographed objects in the night sky and is among the most intensely studied celestial features.

[8] The nebula has revealed much about the process of how stars and planetary systems are formed from collapsing clouds of gas and dust.

[11] Observers have long noted a distinctive greenish tint to the nebula, in addition to regions of red and of blue-violet.

The green hue was a puzzle for astronomers in the early part of the 20th century because none of the known spectral lines at that time could explain it.

This radiation was impossible to reproduce in the laboratory at the time, because it depended on the quiescent and nearly collision-free environment found in the high vacuum of deep space.

[12] There has been speculation that the Mayans of Central America may have described the nebula within their "Three Hearthstones" creation myth; if so, the three would correspond to two stars at the base of Orion, Rigel and Saiph, and another, Alnitak at the southern (left) tip of the "hunter's belt", which together form the vertices of a nearly perfect equilateral triangle, the same shape as traditional Mayan hearths.

[13] Neither Ptolemy's Almagest nor al Sufi's Book of Fixed Stars noted this nebula, even though they both listed patches of nebulosity elsewhere in the night sky; nor did Galileo mention it, even though he also made telescopic observations surrounding it in 1610 and 1617.

[16] The first discovery of the diffuse nebulous nature of the Orion Nebula is generally credited to French astronomer Nicolas-Claude Fabri de Peiresc, on November 26, 1610, when he recorded observing it with a refracting telescope purchased by his patron Guillaume du Vair.

[21] [22])[non-primary source needed] The nebula was independently "discovered" (though visible to the naked eye) by several other prominent astronomers in the following years, including by Giovanni Battista Hodierna (whose sketch was the first published in De systemate orbis cometici, deque admirandis coeli characteribus).

[23] In 1659, Dutch scientist Christiaan Huygens published the first detailed drawing of the central region of the nebula in Systema Saturnium.

[27] In 1902, Vogel and Eberhard discovered differing velocities within the nebula, and by 1914 astronomers at Marseille had used the interferometer to detect rotation and irregular motions.

[30] In 2005, the Advanced Camera for Surveys instrument of the Hubble Space Telescope finished capturing the most detailed image of the nebula yet taken.

[31] A year later, scientists working with the HST announced the first ever masses of a pair of eclipsing binary brown dwarfs, 2MASS J05352184–0546085.

[34] [35] The current astronomical model for the nebula consists of an ionized (H II) region, roughly centered on Theta1 Orionis C, which lies on the side of an elongated molecular cloud in a cavity formed by the massive young stars.

The dark bay that extends from the north into the bright region is known as "Sinus Magnus",[40] also called the "Fish's Mouth".

In 1979 observations with the Lallemand electronic camera at the Pic-du-Midi Observatory showed six unresolved high-ionization sources near the Trapezium Cluster.

[43] In 1993 observations with the Hubble Space Telescope have yielded the major confirmation of protoplanetary disks within the Orion Nebula, which have been dubbed proplyds.

Recent infrared observations show that protoplanetary disks in the Orion Nebula contain dust grains that are growing, beginning the process of forming planetesimals.

[30] Since proplyds are found very close to the Trapezium group, it can be argued that those stars are much younger than the rest of the cluster members.

Each bullet is ten times the diameter of Pluto's orbit and tipped with iron atoms glowing in the infrared.

Whether due to collisions with a spiral arm, or through the shock wave emitted from supernovae, the atoms are precipitated into heavier molecules and the result is a molecular cloud.

This presages the formation of stars within the cloud, usually thought to be within a period of 10–30 million years, as regions pass the Jeans mass and the destabilized volumes collapse into disks.

Over time the ultraviolet light from the massive stars at the center of the nebula will push away the surrounding gas and dust in a process called photoevaporation.

This process is responsible for creating the interior cavity of the nebula, allowing the stars at the core to be viewed from Earth.