1. Interstellar Medium - Wikipedia, The Free Encyclopedia In astronomy, the interstellar medium (or ISM) is the gas and dust that pervade interstellar space the matter that exists between the stars within a galaxy http://en.wikipedia.org/wiki/Interstellar_medium

Interstellar medium From Wikipedia, the free encyclopedia Jump to: navigation search "Interstellar" redirects here. For other uses, see Interstellar (disambiguation) In astronomy , the interstellar medium (or ISM ) is the gas and dust that pervade interstellar space: the matter that exists between the stars within a galaxy . The energy , in the form of electromagnetic radiation , that occupies the same volume is the interstellar radiation field The interstellar medium consists of an extremely dilute (by terrestrial standards) mixture of ions atoms molecules , larger dust grains cosmic rays , and (galactic) magnetic fields (Spitzer 1978). The matter consists of about 99% gas and 1% dust by mass . It fills interstellar space, and blends smoothly into the surrounding intergalactic medium . The ISM is usually extremely tenuous, with densities ranging from a few thousand to a few hundred million particles per cubic meter , and an average value in the Milky Way Galaxy of a million particles per cubic meter. As a result of primordial nucleosynthesis , the gas is roughly 90% hydrogen and 10% helium by number of nuclei , with additional heavier elements metals " in astronomical parlance) present in trace amounts.

2. The Interstellar Medium Approximately 99% of the mass of the interstellar medium is in the form of gas with the remainder primarily in dust. The total mass of the gas and dust in http://csep10.phys.utk.edu/astr162/lect/milkyway/ism.html

The Interstellar Medium As we have noted above, the region between the stars in a galaxy like the Milky Way is far from empty. These regions have very low densities (they constitute a vacuum far better than can be produced artificially on the surface of the Earth), but are filled with gas, dust, magnetic fields, and charged particles. This is commonly termed the interstellar medium Approximately 99% of the mass of the interstellar medium is in the form of gas with the remainder primarily in dust. The total mass of the gas and dust in the interstellar medium is about 15% of the total mass of visible matter in the Milky Way. Gas in the Interstellar Medium Of the gas in the Milky Way, 90% by mass is hydrogen, with the remainder mostly helium. The gas appears primarily in two forms Cold clouds of atomic or molecular hydrogen Hot ionized hydrogen near hot young stars The clouds of cold molecular and atomic hydrogen represent the raw material from which stars can be formed in the disk of the galaxy if they become gravitationally unstable and collapse. Although such clouds do not emit visible radiation, they can be detected by their radio frequency emission. HI and HII Regions Ionized hydrogen is produced when the ultraviolet radiation emitted copiously by hot newly-formed stars ionizes surrounding clouds of gas. The characteristic beautiful red colors of emission nebulae like the

3. What Is The Interstellar Medium? Simply put, the interstellar medium is the material which fills the space between the stars. Many people imagine outer space to be a complete vacuum, http://www-ssg.sr.unh.edu/ism/what1.html

Introduction Who What When ... Links What is the Interstellar Medium? Simply put, the interstellar medium is the material which fills the space between the stars. Many people imagine outer space to be a complete vacuum, devoid of any material. Although the interstellar regions are more devoid of matter than any vacuum artificially created on earth, there is matter in space. These regions have very low densities and consist mainly of gas (99%) and dust . In total, approximately 15% of the visible matter in the Milky Way is composed of interstellar gas and dust. Interstellar Gas: Approximately 99% of the interstellar medium is composed of interstellar gas, and of its mass, about 75% is in the form of hydrogen (either molecular or atomic), with the remaining 25% as helium. The interstellar gas consists partly of neutral atoms and molecules , as well as charged particles, such as ions and electrons . This gas is extremely dilute, with an average density of about 1 atom per cubic centimeter. (For comparison, the air we breathe has a density of approximately 30,000,000,000,000,000,000 molecules per cubic centimeter.) Even though the interstellar gas is very dilute, the amount of matter adds up over the vast distances between the stars. The interstellar gas is typically found in two forms:

4. The Interstellar Medium This medium consists of neutral hydrogen gas (HI), molecular gas (mostly H2), ionized gas (HII), and dust grains. Although the interstellar medium is, http://casswww.ucsd.edu/public/tutorial/ISM.html

University of California, San Diego Gene Smith's Astronomy Tutorial The Interstellar Medium Although space is very empty and the stars in the Milky Way are very far apart, the space between the stars contains a very diffuse medium of gas and dust astronomers call the interstellar medium (ISM) . This medium consists of neutral hydrogen gas (HI), molecular gas (mostly H ), ionized gas (HII), and dust grains. Although the interstellar medium is, by several orders of magnitude, a better vacuum than any physicists can create in the laboratory there is still about of 5-10 billion M of gas and dust out there, comprising approximately 5% of the mass of visible stars in the Galaxy. Neutral Hydrogen Gas The Milky Way Galaxy is filled with a very diffuse distribution of neutral hydrogen gas which has a typical density of about 1 atom/cm g/cm ). The interstellar medium is far too cool to excite the UV or optical transitions of hydrogen, but there is a feature at 21 cm wavelength in the radio produced by the spins (magnetic fields) of the hydrogen atom's nuclear proton and orbiting electron. Because the proton and electron are spinning distributions of electric charge they create minute magnetic fields which interact, creating a small energy difference between the state in which the poles are aligned versus counter-aligned. This energy difference corresponds to the energy of radio waves at 21-centimeters. Every once in a while (about once per 500 years) hydrogen atoms will collide, exciting an atom into the higher energy spin-aligned configuration. It will take as long as 30 million years for the atom to jump back to the lower energy state via a

5. The Interstellar Medium E. L. Fitzpatrick; Hot and Cold Gas in Extragalactic SuperbubblesProbing the interstellar medium of the Superbubble LMC2 in the Large Magellanic Cloud http://www.stsci.edu/stsci/meetings/shst2/node83.html

Next: Planetary Science Up: Contents Previous: Stars, Stellar Populations, and SNRs Science with the Hubble Space Telescope II Book Editors: P. Benvenuti, F. D. Macchetto, and E. J. Schreier Electronic Editor: H. Payne The Interstellar Medium Deuterium in the Local Interstellar Medium R. Ferlet, M. Lemoine, and A. Vidal-Madjar GHRS Observations of Interstellar Deuterium toward HZ 43 W. Landsman, U. J. Sofia, P. Bergeron Boron in the Very Metal-Poor Star BD-13 3442 L. M. Rebull, D. K. Duncan, A. M. Boesgaard, C. P. Deliyannis, L. M. Hobbs, J. R. King, and S. Ryan Boron in the Galactic Halo and Disk D. K. Duncan, F. Primas, K. A. Coble, L. M. Rebull, A. M. Boesgaard, C. P. Deliyannis, L. M. Hobbs, J. R. King, and S. Ryan The GHRS and the Heliosphere GHRS Observations of Diffuse Clouds in the Local Bubble C. Gry and O. Dupin Observations of Interstellar Clouds in the Galactic Halo E. L. Fitzpatrick Hot and Cold Gas in Extragalactic Superbubbles-Probing the Interstellar Medium of the Superbubble LMC2 in the Large Magellanic Cloud A. Caulet Gas and Dust Abundances in Diffuse Halo Clouds K. R. Sembach and B. D. Savage

6. Interstellar Medium This set of notes by Nick Strobel covers the interstellar mediumthe effect of dust, emission nebulae, 21 cm radiation, mapping galactic structure, http://www.maa.mhn.de/Scholar/interstmat.html

Interstellar Medium This set of notes by Nick Strobel covers: the interstellar mediumthe effect of dust, emission nebulae, 21 cm radiation, mapping galactic structure, and molecules.These notes will be in outline form to aid in distinguishing various concepts. As a way to condense the text down I'll often use phrases instead of complete sentences. The vocabulary terms are italicized. Contents Interstellar Medium (ISM) Dust Extinction Reddening ... Molecules Molecular clouds Photo Gallery of Nebulae (Under construction) Interstellar Medium (ISM) Index Stuff between the stars. 10-15% of the visible mass of the Galaxy. 99% of the ISM mass is gas; 1% dust. ``So what?'' Why do we worry about the interstellar medium? The interstellar medium affects starlight and stars are formed from ISM! A. Dust Dust -about the size of the wavelength blue light or smaller. Water ice, graphite (Carbon), Silicon in highly flattened flakes or needles. Effects of dust on light: Extinction Extinction dimming of starlight at all wavelengths. In 1930 R.J. Trumpler plots angular diameter of clusters vs. distance to cluster. Distance found from inverse square law of brightness. IF clusters all have nearly same linear diameter s , then the angular diameter should equal a constant size / distance ( theta = s/D ). But he found a

7. Interstellar Medium And The Milky Way This material is called the interstellar medium. The interstellar medium makes up between 10 to 15% of the visible mass of the Milky Way. http://www.astronomynotes.com/ismnotes/s2.htm

Interstellar Medium (ISM) Chapter index in this window Chapter index in separate window This material (including images) is . See my for fair use practices. Select the photographs to display the original source in another window. Most of the ground-based telescope pictures here are from the Anglo-Australian Observatory (AAO-used by permission). Links to external sites will be displayed in another window. Though the space between the stars is emptier than the best vacuums created on the Earth (those are enclosed spaces devoid of matter, not the household cleaning appliances), there is some material between the stars composed of gas and dust. This material is called the interstellar medium . The interstellar medium makes up between 10 to 15% of the visible mass of the Milky Way. About 99% of the material is gas and the rest is ``dust''. Although the dust makes up only about 1% of the interstellar medium, it has much greater effect on the starlight in the visible band-we can out see only roughly 6000 light years in the plane of the Galaxy because of the dust. Without the dust, we would be able to see through the entire 100,000 light year disk of the Galaxy. Observations of other galaxies are done by looking up or down out of the plane of the Galaxy. Dust provides a place for molecules to form. Finally, probably the most of important of all is that stars and planets form from dust-filled clouds. Therefore, let us look at the dust first and then go on to gas. The structure of the Galaxy is mapped from measurements of the gas.

8. Lecture: Interstellar Medium www.astro.virginia.edu/class/hawley/astr124/ism.html interstellar medium (ISM). http://www.astro.virginia.edu/class/hawley/astr124/ism.html

Astronomy 124 The Interstellar Medium Before we begin our extensive discussion regarding the evolution of stars, we must start with a discussion of the stuff out of which stars are made, namely the gas and dust that is present throughout the galaxy. This material is collectively known as the interstellar medium : the material between the stars. One tends to think of outer space as consisting solely of stars separated by great distances with a complete vacuum between them. While it is true that space is mostly empty, there are regions that contain considerable material. This is relative of course. By earthly standards such regions still constitute a pretty good vacuum. For example, the "typical" gas density in space is one atom per cubic centimeter. The best man-made vacuum is about 10 atoms per cubic centimeter. A cc of the air in the room has about 10 atoms in it. The interstellar medium is not uniform in density. Although on average its density is one atom per cc, it can have densities up to a thousand or a million atoms per cc. The interstellar medium is composed of two classes of material: gas and dust . Gas is composed of molecules or atoms of types of gasses, hydrogen being the most abundant. Carbon monoxide, CO, is another common form of gas, as are oxygen and nitrogen. Dust is composed of little bits of solid matter. Dust is very small, on the order of microns (10

9. Astronomy HyperText Book: Interstellar Medium The interstellar medium (ISM) is the stuff between the stars. Most of this stuff consists of gas and dust . The gas content of the ISM continually decreases http://zebu.uoregon.edu/textbook/ism.html

Much Still Under Development The Interstellar Medium (ISM) is the stuff between the stars. Most of this stuff consists of gas and dust . The gas content of the ISM continually decreases with time as new generations of stars form from the collapse of giant molecular clouds. The collapse and fragementation of these clouds give rise to the formation of stellar clusters . Since the mass function of star formation strongly favors the formation of low mass stars, then each new star formation locks up available ISM gas into a reservoir of unevolving low mass stars. Click here for a schematic representation of the form of the mass function. The dust particles are sufficiently small that they scatter short wavelength light more efficiently than long wavelength light. In fact, blue photons are scattered about 10 times more efficiently than red photons. Basic Principle of Photon Scattering Audio Narration is available No Scattering: Photon Source and Detector Audio Narration is available For optical photons, scattering goes as wavelength to the -4 power. In the case of blue photons compared to red photons, this means that blue photons are about 10 times more likely to get scattered than red photons. This is shown in the next animation. Watch the blue photons scatter away from the detector Audio Narration is available Here we see that only the red photon survives the scattering network to reach the detector Interstellar dust make stars appear redder than they really are Audio Narration is available

10. Douglas McGonagle Ph.D. Thesis Nitrogen Chemistry in the interstellar medium. by. Douglas McGonagle. Department of Physics and Astronomy B.A., University of Massachusetts, Amherst http://www.astro.umass.edu/theses/mcg/thesis.html

Nitrogen Chemistry in the Interstellar Medium by Douglas McGonagle Department of Physics and Astronomy B.A., University of Massachusetts, Amherst Ph.D., University of Massachusetts, Amherst Committee Chair: William Irvine Committee Members: C. Read Predmore F. Peter Schloerb Mark Heyer Charles Dickinson, Outside Member Department Chair: John F. Dubach Abstract We have carried out radio observations for the interstellar molecules NO, NS, and HCCN in order to investigate the role of nitrogen in the chemistry of the interstellar medium (ISM). Abundances of these species and implications for chemistry models are discussed. In addition, we have conducted a spectral line survey towards the star forming region Orion(KL) over the frequency range 160-170 GHz, which revealed a large number of spectral features arising from such nitrogen-bearing molecules as NS, HNCO, HCCCN, CH CN, CH CHCN, and CH CH CN. The first detection of interstellar nitric oxide (NO) in the cold dark cloud L134N is reported, and we also confirm the subsequent detection towards TMC-1. The inferred NO fractional abundance relative to molecular hydrogen for L134N is f towards the position of peak SO emission in that cloud. The inferred fractional abundance for TMC-1 is f

11. ADC Quick Reference: Interstellar Medium (ISM) This quick reference page is designed to point the user toward some of the more frequently used ADC dataset holdings regarding the interstellar medium (ISM) http://adc.astro.umd.edu/adc/quick_ref/ref_ism.html

Astronomical Data Center ADC Quick Reference Page: INTERSTELLAR MEDIUM (ISM) in our GALAXY How to use this Page This page contains links to data pertaining to the following subjects: Interstellar Dust Diffuse H I Warm Ionized Medium (WIM) Hot Ionized Medium (HIM) ... Cosmic Rays Find the topic of interest to you and click on any of the references listed. References listed on a yellow background are ADC holdings, and the hyperlink will transfer you to the ADC documentation on that reference, and give you the option of pre-viewing the data product using the ADC Viewer software, or downloading the product through FTP. Also included on this page are links to selected external (non-ADC) resources which may be of interest. These are labelled as 'External links' or 'Additional Websites'. The ADC is not responsible for the content of external sites linked from this page. This quick reference page is designed to point the user toward some of the more frequently used ADC dataset holdings regarding the interstellar medium (ISM). The references listed here constitute only a small fraction of the total references available; if you do not see a topic or reference covered here, you may perform a search of the complete ADC holdings: [Search ADC Archives] INTERSTELLAR DUST Extinction/Reddening 2088B uvby-Beta Data for Local Interstellar Reddening Map (Perry+ 1982) 2062 Catalogue of Extinction Data (Neckel+ 1980) 2114 UV Interstellar Extinction Excesses for 1415 Stars (Savage+ 1985) 2175 Catalogue of 166 Ultraviolet Extinction Curves (Krelowski+ 1992) ... J/A+A/275/549 Environ. dependence of interstellar extinction (Jenniskens+ 1993)

12. The Magnetized Interstellar Medium The Magnetized interstellar medium conference was hold in Antalya, Turkey, on 812 September 2003, supported by the Max-Planck-Institut für Radioastronomie http://www.mpifr-bonn.mpg.de/div/konti/antalya/

Home Proceedings Antalya 8-12 September 2003, Antalya, Turkey The Magnetized Interstellar Medium conference was hold in Antalya, Turkey, on 8-12 September 2003, supported by the Max-Planck-Institut für Radioastronomie and the Akdeniz University. Proceedings are now being printed. Scientific Committee R. Wielebinski (MPIfR, chair), A. Alpar (Sabancý University), R. Beck (MPIfR), B. Gaensler (Harvard University), J.L. Han (NAO/CAS Beijing), T.L. Landecker (DRAO), M.E. Özel (Abant Ýzzet Baysal University), W. Reich (MPIfR), A.R. Taylor (University of Calgary), M. Urbanik (Jagiellonian University), B. Uyanýker (MPIfR) Local Committee Z. Aslan (Akdeniz University), B. Uyanýker (MPIfR), A. Yar-Uyanýker (MPIfR), W. Reich (MPIfR), P. Reich (MPIfR) The meeting will take place at the Antalya Sheraton Hotel Antalya web site Places to see Weather in Antalya Turkish National Observatory Max-Planck Institut f ür Radioastronomie

13. Interstellar Probe Interstellar Probe. Exploring the interstellar medium and the Boundaries of the Heliosphere. Interstellar Probe Report Interstellar Probe Overview http://interstellar.jpl.nasa.gov/

Interstellar Probe Exploring the Interstellar Medium and the Boundaries of the Heliosphere Interstellar Probe Report Interstellar Probe Overview Related Links For more information regarding this website and the Interstellar Probe Project, please contact Dr. Paulett Liewer This site was last updated: February 5, 2002.

14. THE INTERSTELLAR MEDIUM 98-Aug-24-1545 The interstellar medium is an excellent vacuum but there is about one atom per cm3 and a thousand or so specks of dust per cubic kilometer. http://www.physics.uq.edu.au/people/ross/phys2080/ism/ism.htm

THE INTERSTELLAR MEDIUM So far we have talked about stars in the solar neighborhood. But where did they come from, especially the luminous ones which were not here when the dinosaurs ruled the earth? Is there something between the stars? The answer is yes. The interstellar medium is an excellent vacuum but there is about one atom per cm and a thousand or so specks of dust per cubic kilometer. Not much, but space is big. [Earth atmospheric atom density at sea level is 10 cm The gas is primarily H ("X") and He ("Y") and the dust probably H and anything left over such as C,N,O,Mg,Si,Fe... ("Z"). INTERSTELLAR DUST About one percent of the mass of the interstellar medium is in the form of solid (frozen) material called interstellar dust or grains or sometimes cosmic dust. A typical grain might be 50 nm across (vision peaks at 555 nm) and weigh in at a billion atoms. Why talk about dust before gas? Because the dust is what we "see" or more precisely obscures what we expect to see. If you look at the Milky Way you often see spaces that were originally suspected of being holes or tunnels in the galaxy. But how come all these "tunnels" point to earth? Clouds of dust between us and the rest of the milky way explains this and if you look just below kappa Crucis you can see the Coalsack, a remarkable "hole" in the Milky Way. The thing to know is that the predominant gas is completely transparent while dust is very efficient at blocking light. DARK NEBULAE The Milky Way has numerous dark patches and lanes caused by dust blocking the light behind them. In fact you could read a book by the light of the Milky Way if it were not for this obscuration. Some dark nebulae have been named, the Coalsack, the Emu, the Horsehead. The North America nebula is actually an opening in a dusty region. Many gaseous nebulae have associated dust lanes and sometimes small dark regions called Bok globules, possible protostar nurseries, overlie brighter nebulae. Evidently the interstellar medium has large density fluctuations.

15. American Scientist Online Articles in category interstellar medium. An asterisk (*) denotes content restricted to members and subscribers. Type, Title, Author, Issue Date http://www.americanscientist.org/template/AssetsInCategory/categoryid/705

Home Current Issue Archives Bookshelf ... Subscribe In This Section Search Book Reviews by Issue Issue Index Topical Index ... Classics Site Search Advanced Search Visitor Login Username Password Help with login Forgot your password? Change your username Articles in category: Interstellar Medium An asterisk (*) denotes content restricted to members and subscribers. Type Title Author Issue Date Feature Article The Galactic Environment of the Sun Priscilla Frisch January-February 2000 ADVERTISEMENTS About American Scientist Site Map Text Archive ... Contact Us

16. Interstellar Medium: Cold Maps of interstellar reddening demonstrated that the interstellar medium is composed mostly of hydrogen and helium gas (99%) and traces of dust. http://abyss.uoregon.edu/~js/ast122/lectures/lec22.html

Interstellar Medium When one looks up into the night sky we only see stars and the occasional planet. Most of outer space is empty, meaning that the density of atoms is much lower than even the best vacuums in our labs. Deep imaging of the skies showed that there are numerous regions where interstellar matter, in the form of gas and dust, collects to form clouds and nebula. Since these clouds are diffuse, they are difficult to see with the naked eye. The first indication that there was interstellar gas and dust was dark lanes in the Milky Way. Since we live in a disk galaxy, then looking outward we see a band of light in the sky which, if magnified, breaks down into the many stars in our Galaxy. A deep photo of the Milky Way shows that there are dark regions or lanes. We understand now that there is gas and dust blocking the starlight which produces these dark lanes, such as the CoalSack Nebula . In fact, most of our Galaxy is blocked from our view by patches of gas and dust Interstellar Extinction Astrophotograph in the 19th century showed that the dark lanes or holes in the Milky Way did not have sharp edges. That, in fact, detail studies of star clusters at various distances from us showed that the intensity of light from remote stars is reduced as it passes through the sparse material of the interstellar medium. Herschel tried to use star counts to measure the size of the Galaxy and where our position is within it. His result was the diagram below, but what he really discovered was that interstellar extinction limits our line of sight.

17. Interstellar Medium interstellar medium. in order for an interstellar cloud to collapse gravitationally, it must. A not have any spin. B have a very large mass. http://webs.wichita.edu/astronomy/Testbank/ism.htm

Interstellar medium in order for an interstellar cloud to collapse gravitationally, it must A not have any spin. B have a very large mass. C be made mostly of hydrogen. D have a low internal pressure compared to its gravity. E have a high internal pressure compared to its gravity. 21-cm radiation has yielded important information about A the density of helium in the universe B the physical structure of our galaxy C the prevalence of water in the universe D the spin-flip propensities of methyl alcohol (ch2oh) dark clouds are best studied through examination of A interstellar absorption lines in the spectra of distant stars B Balmer emission lines C radio waves emitted by molecules D ultraviolet radiation emitted by the gas interstellar molecules are most abundant in A dark clouds B emission nebulae C reflection nebulae D between spiral arms interstellar 21-cm radiation is emitted by A water B methyl alcohol C helium D hydrogen most interstellar molecules reveal their presence by radiating A infrared wavelengths B ultraviolet wavelengths C x-rays D radio wavelengths the 21-centimeter line arises from which of the following?

18. The Violent Interstellar Medium Of Nearby Dwarf Galaxies The Violent interstellar medium of Nearby Dwarf Galaxies. http://www.atnf.csiro.au/pasa/16_1/walter/paper/

The Violent Interstellar Medium of Nearby Dwarf Galaxies Fabian Walter, PASA, 16 (1), 106 The html and gzipped postscript versions of this paper are in preprint form. To access the final published version, download the pdf file Next Section: On Holes and Shells Contents Page: Volume 16, Number 1 The Violent Interstellar Medium of Nearby Dwarf Galaxies Fabian Walter Radioastronomisches Institut, Bonn, Germany E-mail: walter@astro.uni-bonn.de Abstract: High resolution H I Keywords: galaxies: individual (IC 2574, Holmberg II, DDO 47, NGC 3077), ISM: kinematic and dynamics, ISM: structure, radio lines: ISM, X-rays: ISM On Holes and Shells in Galaxies Holes in Dwarfs vs. Holes in Spirals So, what created the holes? The case of the Supergiant shell in IC2574 ... Astronomical Society of Australia

19. Notes On The Interstellar Medium For Asph 503 This page gives links that are useful for the students in ASPH503, the interstellar medium course here at U of Calgary. Below are links to PDF forms of my http://www.iras.ucalgary.ca/~volk/asph503.html

This page gives links that are useful for the students in ASPH503, the Interstellar Medium course here at U of Calgary. Below are links to PDF forms of my class notes; the PDF conversion is not always 100% correct for some reason that I have not been able to determine. However I think the files can be printed if desired. PDF (portable document format) is from Adobe Systems, and the Adobe Acrobat reader is needed to view them. The notes more or less replace a textbook, since the field is moving so rapidly and all the available textbooks that I know of are out of date. I have much more emphasis on molecular cloud properties and star formation than is normal in ISM textbooks, since these areas are two of the currently most active aspects of ISM research. The same is true of extragalactic ISM research, but there I was only able to put in a small amount of material mostly for comparison with the situation in the Galaxy. One thing that I could not make for the notes was a copy of the Columbia CO map of the Galaxy by Dame et al. This is refered to in the notes and there are some filler pages where I photocopied the original large-scale map from T. M. Dame et al. (1987; ApJ, 322, 706-720). A nice colour poster of this map is available from Dr. Dame. Some WWW images from the poster are found at this link These notes are free for the downloading, but I stress that they are by no means perfect or even polished. Some parts of them may reflect my ignorance rather than my knowledge. It was educational for me to put the notes together; things have changed a lot since I took this sort of course in 1981.

20. APOD: 2002 February 10 - The Local Interstellar Cloud In the disk of our Milky Way Galaxy about 10 percent of visible matter is in the form of gas, called the interstellar medium (ISM). The ISM is not uniform, http://apod.nasa.gov/apod/ap020210.html

Astronomy Picture of the Day Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2002 February 10 The Local Interstellar Cloud Linda Huff ( American Scientist Priscilla Frisch U. Chicago Explanation: The stars are not alone. In the disk of our Milky Way Galaxy about 10 percent of visible matter is in the form of gas, called the interstellar medium (ISM). The ISM is not uniform, and shows patchiness even near our Sun . It can be quite difficult to detect the local ISM because it is so tenuous and emits so little light. This mostly hydrogen gas, however, absorbs some very specific colors that can be detected in the light of the nearest stars . A working map of the local ISM within 10 light-years based on recent observations is shown above . These observations show that our Sun is moving through a Local Interstellar Cloud as this cloud flows outwards from the Scorpius-Centaurus Association star forming region. Our Sun may exit the Local Interstellar Cloud during the next 10,000 years. Much remains unknown about the local

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