[[Image:Barnard 68.jpg|thumb|500pix.jpg|left|Molekularni oblak [[Barnard 68]], oko 500 svetlosnih godina udaljen i 0,5 svetlosnih godina u prečniku.]]
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Unutar [[Milky Way|Mlečnog puta]], molecular gas clouds account for less than one percent of the volume of the [[interstellar medium]] (ISM), yet it is also the densest part of the medium, comprising roughly half of the total gas mass interior to the [[Sun]]'s galactic orbit. The bulk of the molecular gas is contained in a ring between {{convert|3.5|and|7.5|kpc|ly|lk=on|abbr = off}} from the center of the Milky Way (the Sun is about 8.5 kiloparsecs from the center).<ref name="ferriere2001">{{cite journal | author=Ferriere, D. | title= The Interstellar Environment of our Galaxy | journal=Reviews of Modern Physics | date=2001| volume=73 | issue=4 | pages= 1031–1066 | doi = 10.1103/RevModPhys.73.1031 | bibcode=2001RvMP...73.1031F|arxiv = astro-ph/0106359 | s2cid= 16232084 }}</ref> Large scale CO maps of the galaxy show that the position of this gas correlates with the spiral arms of the galaxy.<ref>{{cite journal | author=Dame | title=A composite CO survey of the entire Milky Way | journal=Astrophysical Journal | date=1987| volume=322 | pages= 706–720 | doi = 10.1086/165766 | last2=Ungerechts | first2=H. | last3=Cohen | first3=R. S. | last4=De Geus | first4=E. J. | last5=Grenier | first5=I. A. | last6=May | first6=J. | last7=Murphy | first7=D. C. | last8=Nyman | first8=L.-A. | last9=Thaddeus | first9=P. | bibcode=1987ApJ...322..706D | hdl=1887/6534 | display-authors=1| url=https://openaccess.leidenuniv.nl/bitstream/handle/1887/6534/ApJ_322_706_720.pdf?sequence=1 }}</ref> That molecular gas occurs predominantly in the spiral arms suggests that molecular clouds must form and dissociate on a timescale shorter than 10 million years—the time it takes for material to pass through the arm region.<ref name="williams2000">{{cite conference | first1 = J. P. | last1 = Williams | last2 = Blitz | first2 = L. | last3 = McKee | first3 = C. F. | title = The Structure and Evolution of Molecular Clouds: from Clumps to Cores to the IMF | book-title = Protostars and Planets IV | pages = 97 | publisher = Tucson: University of Arizona Press | date = 2000 | arxiv = astro-ph/9902246 |bibcode = 2000prpl.conf...97W }}</ref>▼
▲Unutar [[Milky Way|Mlečnog puta]], molecularoblaci gasmolekularnih cloudsgasova accountčine formanje lessod thanjednog oneprocenta percent of the volume of thezapremine [[interstellar medium|međuzvezdanog medijuma]] ({{jez-eng-lat|interstellar medium - ISM}}), yetali itje isto alsoistovremeno thei densestnajgušći partdeo of the mediummedijuma, comprisingkoji roughlyobuhvata halfpribližno ofpolovinu theukupne totalunutrašnjosti gasgasne massmase interior to theu [[Sun|Sunčevoj]]'sgalacticgalaktičkoj orbitorbiti. TheGlavnina bulkmolekularnog ofgasa thesadržana molecularje gasu isprstenu containedizmeđu in3,5 ai ring7,5 betweenkiloparseka {{convert|3(110.5|and|7.5|kpc|ly|lk=on|abbr000 =i off}}240.000 from[[svetlosna thegodina|svetlosnih centergodina]]) ofod thecentra MilkyMlečnog Wayputa (theSunce Sunje isudaljeno aboutoko 8.,5 kiloparsecskiloparseka from theod centercentra).<ref name="ferriere2001">{{cite journal | author=Ferriere, D. | title= The Interstellar Environment of our Galaxy | journal=Reviews of Modern Physics | date=2001| volume=73 | issue=4 | pages= 1031–1066 | doi = 10.1103/RevModPhys.73.1031 | bibcode=2001RvMP...73.1031F |arxiv = astro-ph/0106359 | s2cid= 16232084 }}</ref> Large scaleKarte -{CO}- mapsvelikih ofrazmera theu galaxygalaksiji showpokazuju thatda theje positionpoložaj ofovog thisgasa gasu correlateskorelaciji withsa thespiralnim spiral arms of thekrakovima galaxygalaksije.<ref>{{cite journal | author=Dame | title=A composite CO survey of the entire Milky Way | journal=Astrophysical Journal | date=1987| volume=322 | pages= 706–720 | doi = 10.1086/165766 | last2=Ungerechts | first2=H. | last3=Cohen | first3=R. S. | last4=De Geus | first4=E. J. | last5=Grenier | first5=I. A. | last6=May | first6=J. | last7=Murphy | first7=D. C. | last8=Nyman | first8=L.-A. | last9=Thaddeus | first9=P. | bibcode=1987ApJ...322..706D | hdl=1887/6534 | display-authors=1| url=https://openaccess.leidenuniv.nl/bitstream/handle/1887/6534/ApJ_322_706_720.pdf?sequence=1 }}</ref> ThatDa molecularse molekularni gas occurspretežno predominantlyjavlja inu thespiralnim spiralkrakovima, armssugeriše suggestsse thatda molecularse cloudsmolekularni mustoblaci formmoraju andformirati dissociatei onrazdvojiti au timescalevremenskom shorterokviru thankraćem od 10 millionmiliona years—thegodina time- itvremenu takeskoje forje materialpotrebno toda passmaterijal throughprođe thekroz armregion regionkraka.<ref name="williams2000">{{cite conference | first1 = J. P. | last1 = Williams | last2 = Blitz | first2 = L. | last3 = McKee | first3 = C. F. | title = The Structure and Evolution of Molecular Clouds: from Clumps to Cores to the IMF | book-title = Protostars and Planets IV | pages = 97 | publisher = Tucson: University of Arizona Press | date = 2000 | arxiv = astro-ph/9902246 |bibcode = 2000prpl.conf...97W }}</ref>
[[File:Violent birth announcement from an infant star.jpg|thumb|Circinus molecular cloud has a mass around 250,000 times that of the Sun.<ref>{{cite news|title=Violent birth announcement from an infant star|url=http://www.spacetelescope.org/images/potw1421a/|access-date=27 May 2014|newspaper=ESA/Hubble Picture of the Week}}</ref>]]▼
Vertically to the plane of the galaxy, the molecular gas inhabits the narrow midplane of the galactic disc with a characteristic [[scale height]], ''Z'', of approximately 50 to 75 parsecs, much thinner than the warm [[atom]]ic (''Z ''from 130 to 400 parsecs) and warm [[ion]]ized (''Z ''around 1000 parsecs) gaseous [[Interstellar medium#Interstellar matter|components of the ISM]].<ref>{{cite journal | author=Cox, D. | date=2005 | title=The Three-Phase Interstellar Medium Revisited | journal=Annual Review of Astronomy and Astrophysics | volume=43 | issue=1 | pages=337–385 | doi=10.1146/annurev.astro.43.072103.150615 | bibcode=2005ARA&A..43..337C}}</ref> The exception to the ionized-gas distribution are [[H II region]]s, which are bubbles of hot ionized gas created in molecular clouds by the intense radiation given off by [[OB star|young massive stars]] and as such they have approximately the same vertical distribution as the molecular gas.▼
▲[[File:Violent birth announcement from an infant star.jpg|thumb|CircinusMolekularni molecularoblak cloud[[Шестар has(сазвежђе)|Šestara]] aima massmasu aroundoko 250,.000 timesputa thatveću ofod themase SunSunca.<ref>{{cite news|title=Violent birth announcement from an infant star|url=http://www.spacetelescope.org/images/potw1421a/|access-date=27 May 2014|newspaper=ESA/Hubble Picture of the Week}}</ref>]]
This distribution of molecular gas is averaged out over large distances; however, the small scale distribution of the gas is highly irregular with most of it concentrated in discrete clouds and cloud complexes.<ref name="ferriere2001" />
▲VerticallyVertikalno tou theodnosu planena of theravan galaxygalaksije, the molecularmolekularni gas inhabitsnaseljava theusku narrowsrednju midplaneravan ofgalaktičkog thediska galactic disc with a characteristickarakteristične [[scale height|skale visine]], ''Z'',ofod approximatelypribližno 50 todo 75 parsecsparseka, muchmnogo thinnertanje thanod the warmtople [[atom]]icske (''Z''from od 130 todo 400 parsecs parseka) andi warmtople [[ionjon]]izedizovane (''Z''around oko 1000 parsecs parseka) gaseousgasovite [[Interstellar medium#Interstellar matter|components of thekomponente ISM]].<ref>{{cite journal | author=Cox, D. | date=2005 | title=The Three-Phase Interstellar Medium Revisited | journal=Annual Review of Astronomy and Astrophysics | volume=43 | issue=1 | pages=337–385 | doi=10.1146/annurev.astro.43.072103.150615 | bibcode=2005ARA&A..43..337C}}</ref> TheIzuzetak exceptionod todistribucije thejonizovanog ionized-gasgasa distribution aresu [[HII regioni|regioni -{H II region}-]]s, whichkoji aresu bubblesmehuri ofvrućeg hotjonizovanog ionizedgasa gasstvoreni createdu inmolekularnim molecularoblacima cloudsintenzivnim byzračenjem thekoje intense radiation given off bydaju [[OB star|youngmlade massivemasivne starszvezde]] and as such theyi havekao approximatelytakvi theimaju samepribližno verticalistu distributionvertikalnu asdistribuciju thekao molecularmolekularni gas.
Ova raspodela molekularnog gasa je prosečena na velikim udaljenostima; međutim, distribucija gasa u malim razmerama je vrlo nepravilna, s tim što je većina koncentrisana u diskretnim oblacima i oblačnim kompleksima.<ref name="ferriere2001" />
