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). A Plasma lamp, illustrating some of the more complex phenomena of a plasma, including filamentation In physics and chemistry, a plasma is an ionized gas, and is usually considered to be a distinct phase of matter. ... This article describes dust in the astronomical cosmic context, of which interplanetary dust and interstellar dust are particular types. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light years in diameter and approximately 60 million light years distant. ... The distribution of ionized hydrogen (known by astronomers as H II (aitch two) from old spectroscopic terminology) in the parts of the Galactic interstellar medium visible from the Earths northern hemisphere (from the Wisconsin H-Alpha Mapper Survey) In astronomy, the interstellar medium (or ISM) is the matter and... Italic textLink titleLink titlelink titlelink titleBold text General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... An H I region is an interstellar cloud composed of warm 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 molecular hydrogen, H2. ...

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. ... Categories: Astronomy stubs | Nebulae | NGC objects ...

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 radiation can be conceptualized as a self propagating transverse oscillating wave of electric and magnetic fields. ... The 64 metre radio telescope at Parkes Observatory, New South Wales, Australia In contrast to an ordinary telescope, which produces visible light images, a radio telescope sees radio waves emitted by radio sources, typically by means of a large parabolic (dish) antenna, or arrays of them. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... Electromagnetic spectroscopy a. ... The wavelength is the distance between repeating units of a wave pattern. ...

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 metre radio telescope at Parkes Observatory, New South Wales, Australia In contrast to an ordinary telescope, which produces visible light images, a radio telescope sees radio waves emitted by radio sources, typically by means of a large parabolic (dish) antenna, or arrays of them. ...

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 only occur 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 that part of chemistry concerned with the composition, structure, properties, reactions and synthesis of organic compounds. ... 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 composed primarily of neutral hydrogen, and typically have a lower portion of heavy elements than is normal for interstellar clouds in the Milky Way. Note: This article contains special characters. ... Italic textLink titleLink titlelink titlelink titleBold text General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ...

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 later is the Magellanic Stream. Map of the local group The Local Group is the group of galaxies that includes our galaxy, the Milky Way. ... // 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

The distribution of ionized hydrogen (known by astronomers as H II (aitch two) from old spectroscopic terminology) in the parts of the Galactic interstellar medium visible from the Earths northern hemisphere (from the Wisconsin H-Alpha Mapper Survey) In astronomy, the interstellar medium (or ISM) is the matter and... This is a list of molecules that have been detected in the interstellar medium, as of 2003. ...

External links

• High Velocity Cloud — The SAO encyclopedia.