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The history of nebulae begins shortly after the invention of the [[telescope]]. In 1610,  Nicolas-Claude Fabri de Peiresc first observed the [[Orion nebula]].<ref name=britannica>[https://www.britannica.com/topic/nebula#ref61216 Nebula] from britannica.com</ref> He was the first to notice that the nebula was not a [[star]] as it appears to the naked eye. Later in 1656, [[Christiaan Huygens]] described the inner regions of the nebula and that there was in fact 4 stars at the centre Orion nebula.

The history of nebulae begins shortly after the invention of the [[telescope]]. In 1610,  Nicolas-Claude Fabri de Peiresc first observed the [[Orion nebula]].<ref name=britannica>[https://www.britannica.com/topic/nebula#ref61216 Nebula] from britannica.com</ref> He was the first to notice that the nebula was not a [[star]] as it appears to the naked eye. Later in 1656, [[Christiaan Huygens]] described the inner regions of the nebula and that there was in fact 4 stars at the centre Orion nebula.

Later on in the 18^th century, [[astronomer]]s were searching for [[comet]]s in the night sky. At that time, both nebulae and comets appeared as fuzzy region when viewed through their telescopes. As a result some astronomers mistook nebulae for comets. To counter this, astronomers began to catalogue nebulae to avoid confusion. The most well known catalogue is the [[Messier catalogue]], a collection of over 100 objects noted by [[Charles Messier]] and published in 1781.<ref name=britannica/> It is important to note that not all these objects are nebulae. Some objects like [[galaxies]] were originally referred to as nebulae as they possess a similar appearance through the telescopes available at that time.

Later on in the 18^th century, [[astronomer]]s were searching for [[comet]]s in the night sky. At that time, both nebulae and comets appeared as fuzzy region when viewed through their telescopes. As a result, some astronomers mistook nebulae for comets. To counter this, astronomers began to catalogue nebulae to avoid confusion. The most well known catalogue is the [[Messier catalogue]], a collection of over 100 objects noted by [[Charles Messier]] and published in 1781.<ref name=britannica/> It is important to note that not all these objects are nebulae. Some objects like [[galaxies]] were originally referred to as nebulae as they possess a similar appearance through the telescopes available at that time.

In the 19^th century, the astronomer [[William Herschel]] and his son [[John Herschel]] discovered thousands of nebulae, far more than anyone else.<ref name=britannica/> In the years between 1786 and 1802, William Herschel with help from his sister Caroline discovered at least 2,500 clusters, nebulae and [[galaxies]]. John Herschel discovered a further 1,700 objects. These discoveries form a major components of the [[New General Catalogue]] created by John Dreyer in 1888.<ref name=britannica/> Together, these form 4,630 of the 7,840 objects in the catalogue.<ref>[https://www.space.com/17432-william-herschel.html William Herschel] from space.com</ref>

In the 19^th century, the astronomer [[William Herschel]] and his son [[John Herschel]] discovered thousands of nebulae, far more than anyone else.<ref name=britannica/> In the years between 1786 and 1802, William Herschel with help from his sister Caroline discovered at least 2,500 clusters, nebulae and [[galaxies]]. John Herschel discovered a further 1,700 objects. These discoveries form a major components of the [[New General Catalogue]] created by John Dreyer in 1888.<ref name=britannica/> Together, these form 4,630 of the 7,840 objects in the catalogue.<ref>[https://www.space.com/17432-william-herschel.html William Herschel] from space.com</ref>

Nebulae come in a variety of shapes and size, ranging from less than 1 [[light year]] across to hundreds of light years across. There are several different classifications of nebulae including [[diffuse nebulae]], [[planetary nebulae]] and [[dark nebulae]]. Diffuse nebulae are further split up into [[emission nebula]]e and [[reflection nebula]]e. All nebulae however consist of large clouds of gas and dust. Temperatures inside nebulae vary depending on the type but can be anywhere from 10 [[Kelvin|K]] to as high as 10 million K.<ref name=britannica/> Large nebulae can contain over ten thousand [[solar mass]]es of material.<ref name=aig-splendor/>

Nebulae come in a variety of shapes and size, ranging from less than 1 [[light year]] across to hundreds of light years across. There are several different classifications of nebulae including [[diffuse nebulae]], [[planetary nebulae]] and [[dark nebulae]]. Diffuse nebulae are further split up into [[emission nebula]]e and [[reflection nebula]]e. All nebulae however consist of large clouds of gas and dust. Temperatures inside nebulae vary depending on the type but can be anywhere from 10 [[Kelvin|K]] to as high as 10 million K.<ref name=britannica/> Large nebulae can contain over ten thousand [[solar mass]]es of material.<ref name=aig-splendor/>

Most nebulae have a very similar composition, with around 90% of the [[atom]]s in the nebulae being [[hydrogen]] and much of the remaining 10% being [[helium]].<ref name=britannica/> This lead to nebulae containing [[ionization|ionized]] hydrogen being called "H II regions," as "H II" is commonly used to denote to singly ionized hydrogen in astronomy. Other elements like [[nitrogen]], [[oxygen]] and [[neon]] are often found as well at around two parts per thousand.<ref name=britannica/> Compounds and [[organic molecule]]s such as [[cyanide|hydrogen cyanide]], [[formaldehyde]] and [[methanol]] have also been observed in the [[Orion nebula]].<ref name=herschel/> Interstellar dust composed of [[carbon]] and [[silicate]]s accounts for a fraction (0.7%) of the material in nebulae.<ref name=britannica/> Typical densities in nebulae vary from hundreds to millions of hydrogen atoms per cubic centimetre.

Most nebulae have a very similar composition, with around 90% of the [[atom]]s in the nebulae being [[hydrogen]] and much of the remaining 10% being [[helium]].<ref name=britannica/> This led to nebulae containing [[ionization|ionized]] hydrogen being called "H II regions," as "H II" is commonly used to denote to singly ionized hydrogen in astronomy. Other elements like [[nitrogen]], [[oxygen]] and [[neon]] are often found as well at around two parts per thousand.<ref name=britannica/> Compounds and [[organic molecule]]s such as [[cyanide|hydrogen cyanide]], [[formaldehyde]] and [[methanol]] have also been observed in the [[Orion nebula]].<ref name=herschel/> Interstellar dust composed of [[carbon]] and [[silicate]]s accounts for a fraction (0.7%) of the material in nebulae.<ref name=britannica/> Typical densities in nebulae vary from hundreds to millions of hydrogen atoms per cubic centimetre.

==Classification==

==Classification==