Changes

*[[Diffuse nebulae]] - These are large but thin clouds of gas and dust.<ref name=seds-diffuse>[http://www.messier.seds.org/diffuse.html Diffuse Nebulae] from messier.seds.org</ref> These are sub classified into two types, [[emission nebula]]e and [[reflection nebula]]e. Emission nebulae, also known as H II regions, occur when high energy [[radiation]] from nearby large stars causes the nebulae to glow, normally a red color. If there are no large stars, then there may be a reflection nebulae, where the white/blue light of stars is reflected off dust.<ref name=seds-diffuse/> This produces a blue nebula. Examples include the [[Lagoon nebula]] and the [[Eagle nebula]].

*[[Diffuse nebulae]] - These are large but thin clouds of gas and dust.<ref name=seds-diffuse>[http://www.messier.seds.org/diffuse.html Diffuse Nebulae] from messier.seds.org</ref> These are sub classified into two types, [[emission nebula]]e and [[reflection nebula]]e. Emission nebulae, also known as H II regions, occur when high energy [[radiation]] from nearby large stars causes the nebulae to glow, normally a red color. If there are no large stars, then there may be a reflection nebulae, where the white/blue light of stars is reflected off dust.<ref name=seds-diffuse/> This produces a blue nebula. Examples include the [[Lagoon nebula]] and the [[Eagle nebula]].

*[[Planetary nebulae]] - These nebulae tend to be faint, fairly small (perhaps a few light years across) and are often circular or ring shaped with a shell-like structure.<ref name=seds-planetary>[http://www.messier.seds.org/planetar.html Planetary Nebulae] from messier.seds</ref> These were named "planetary nebulae" due to their resemblance to [[planet]]s when viewed through a telescope. They are often found to be expanding at a few tens of kilometres per second. Examples of planetary nebulae include the [[Ring nebula]], the [[Cat's eye nebula]] and the [[Butterfly nebula]].

*[[Planetary nebulae]] - These nebulae tend to be faint, fairly small (perhaps a few light years across) and are often circular or ring shaped with a shell-like structure.<ref name=seds-planetary>[http://www.messier.seds.org/planetar.html Planetary Nebulae] from messier.seds</ref> These were named "planetary nebulae" due to their resemblance to [[planet]]s when viewed through a telescope. They are often found to be expanding at a few tens of kilometres per second. Examples of planetary nebulae include the [[Ring nebula]], the [[Cat's eye nebula]] and the [[Butterfly nebula]].

*[[Dark nebulae]] - Also called molecular clouds, these nebulae are characterised by interstellar dust in the foreground, obscuring stars or a bright nebula in the background.<ref name=britannica-dark>[https://www.britannica.com/topic/molecular-cloud Molecular Clouds] from britannica.com</ref> Some times called absorption nebulae, dark nebulae tend to be very dense and cold. Due to their dark nature, they can only really be seen via far-infrared and [[microwave]] techniques and have a temperature of 7-15 K.,ref name=britannica-dark Well known examples include the [[Horsehead nebula]] and the [[Coalsack nebula]].

*[[Dark nebulae]] - Also called molecular clouds, these nebulae are characterised by interstellar dust in the foreground, obscuring stars or a bright nebula in the background.<ref name=britannica-dark>[https://www.britannica.com/topic/molecular-cloud Molecular Clouds] from britannica.com</ref> Some times called absorption nebulae, dark nebulae tend to be very dense and cold. Due to their dark nature, they can only really be seen via far-infrared and [[microwave]] techniques and have a temperature of 7-15 K.<ref name=britannica-dark/> Well known examples include the [[Horsehead nebula]] and the [[Coalsack nebula]].

*[[Supernova]] remnants - These are the remnants of supernovae, composed of gas emitted during the supernova explosion.<ref name=seds-supernova>[http://www.messier.seds.org/snr.html Supernova Remnants (SNR's)] from messier.seds.org</ref> They are often large and impressive. Only a handful have been observed in the [[Milky Way]], but others have been seen in other [[galaxies]]. Examples include the [[Crab Nebula|Crab nebula]] and [[SN 1604]].

*[[Supernova]] remnants - These are the remnants of supernovae, composed of gas emitted during the supernova explosion.<ref name=seds-supernova>[http://www.messier.seds.org/snr.html Supernova Remnants (SNR's)] from messier.seds.org</ref> They are often large and impressive. Only a handful have been observed in the [[Milky Way]], but others have been seen in other [[galaxies]]. Examples include the [[Crab Nebula|Crab nebula]] and [[SN 1604]].