Interstellar cloud is the generic name given to an accumulation of gas, plasma and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium. Depending on the density, size and temperature of a given cloud, the hydrogen in it can be neutral (H I regions), ionized (H II regions) (ie. a plasma), or molecular (molecular clouds). Neutral and ionized clouds are sometimes also called diffuse clouds, while molecular clouds are sometimes also referred to as dense clouds. For other uses, see Plasma. ... “Space dust” redirects here. ... For other uses, see Galaxy (disambiguation). ... The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ... For other uses, see Density (disambiguation). ... This article is about the chemistry of hydrogen. ... An H I region (pronounced aitch one region) is an interstellar cloud composed of neutral atomic hydrogen (H1). ... NGC 604, a giant H II region in the Triangulum Galaxy. ... A molecular cloud is a type of interstellar cloud whose density and size permits the formation of molecules, most commonly molecular hydrogen (H2). ... Ionization is the physical process of converting an atom or molecule into an ion by changing the difference between the number of protons and electrons. ...

Over 200 newly formed stars are scattered within a cavern-like, gaseous, interstellar cloud (NGC 604). The stars irradiate the gas with energetic ultraviolet light stripping electrons from atoms and exciting them—producing a characteristic nebular glow.

The nebula cataloged as NGC 604 is a giant star forming region, 1500 light years across, in the nearby spiral galaxy, M33. ... The nebula cataloged as NGC 604 is a giant star forming region, 1500 light years across, in the nearby spiral galaxy, M33. ... This article is about the astronomical object. ... Categories: Astronomy stubs | Nebulae | NGC objects ... Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ... For other uses, see Electron (disambiguation). ... Properties For other meanings of Atom, see Atom (disambiguation). ... The Triangulum Emission Nebula NGC 604 The Pillars of Creation from the Eagle Nebula For other uses, see Nebula (disambiguation). ...

Chemical compositions

Analysing the composition of interstellar clouds is achieved by studying electromagnetic radiation that we receive from them. Large radio telescopes scan the intensity in the sky of particular frequencies of electromagnetic radiation which are characteristic of certain molecules' spectra. Some interstellar clouds are cold and tend to give out EM radiation of large wavelengths. We can produce a map of the abundance of these molecules to produce an understanding of the varying composition of the clouds. In hot clouds, there are often ions of many elements, whose spectra can be seen in visible and ultraviolet light. Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... The 64 meter radio telescope at Parkes Observatory A radio telescope is a form of directional radio antenna used in radio astronomy and in tracking and collecting data from satellites and space probes. ... For other uses, see Frequency (disambiguation). ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... Electromagnetic spectroscopy a. ... For other uses, see Wavelength (disambiguation). ... The periodic table of the chemical elements A chemical element, or element, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ...

Radio telescopes can also scan over the frequencies from one point in the map, recording the intensities of each type of molecule. Peaks of frequencies mean that an abundance of that molecule or atom is present in the cloud. The height of the peak is proportional to the relative percentage that it makes up. The 64 meter radio telescope at Parkes Observatory A radio telescope is a form of directional radio antenna used in radio astronomy and in tracking and collecting data from satellites and space probes. ...

Unexpected chemicals detected in interstellar clouds

Until recently the rates of reactions in interstellar clouds were expected to be very slow, with minimal products being produced due to the low temperature and density of the clouds. However, large organic molecules were observed in the spectra that scientists would not have expected to find under these conditions. The reactions needed to create them normally occur only at much higher temperatures and pressures. The fact that they were found indicates that these chemical reactions in interstellar clouds take place faster than suspected. These reactions are studied in the CRESU experiment. Organic chemistry is a specific discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of chemical compounds consisting primarily of carbon and hydrogen, which may contain any number of other elements, including nitrogen, oxygen, halogens as well... This article is about the profession. ... For other uses, see Chemical reaction (disambiguation). ... The CRESU experiment (meaning Cinétique de Réaction en Ecoulement Supersonique Uniforme, or Reaction Kinetics in Uniform Supersonic Flow) is an experiment investigating chemical reactions taking place at very low temperatures. ...

High-velocity cloud

These interstellar clouds possess a velocity higher than can be explained by the rotation of the Milky Way. They are detected primarily in the 21 cm line of neutral hydrogen, and typically have a lower portion of heavy elements than is normal for interstellar clouds in the Milky Way. For other uses, see Milky Way (disambiguation). ... This article or section does not adequately cite its references or sources. ... This article is about the chemistry of hydrogen. ...

Theories intended to explain these unusual clouds include materials left over from the formation of our galaxy, or tidally-displaced matter drawn away from other galaxies or members of the Local Group. An example of the latter is the Magellanic Stream. Comet Shoemaker-Levy 9 after breaking up under the influence of Jupiters tidal forces. ... This article is about matter in physics and chemistry. ... A member of the Local Group of galaxies, irregular galaxy Sextans A is 4. ... // Introduction Hierarchical Clustering tells us that galaxies are built up over time from collisions of smaller galaxies. ...

High-velocity clouds are identified with a HVC prefix, as with HVC 127-41-330. HVC 127-41-330 is a high velocity cloud located at that galactic longitude, latitude, and velocity towards Earth. ...

See also

• Interstellar medium
• List of molecules in interstellar space
• Nebula

The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ... This is a list of molecules that have been detected in the interstellar medium, grouped by the number of component atoms. ... The Triangulum Emission Nebula NGC 604 The Pillars of Creation from the Eagle Nebula For other uses, see Nebula (disambiguation). ...

External links

• High Velocity Cloud — The Swinburne Astronomy Online (SAO]] encyclopedia.