1. Interstellar Medium Learning Pages After you have learned the basics, move on to The interstellar medium In Depth. http://www-ssg.sr.unh.edu/tof/Outreach/Interstellar/

Although the subject may sound INTIMIDATING... It does not have to be. Begin here with the basics: After you have learned the basics, move on to...

2. The Local Interstellar Medium Introduction the Local interstellar medium. Overall Picture. Opacity of the ISM By the "Local interstellar medium (LISM)", we mean the gas occupying the space between the stars out http://spacsun.rice.edu/~twg/lism.html

3. The Interstellar Medium Gas in the interstellar medium. Of the gas in the Milky Way, 90% by mass is hydrogen,with the remainder mostly helium. Dust in the interstellar medium. 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

4. Astronomy Supplement - The Interstellar Medium Astronomy Supplement 16. The interstellar medium. Latest Modification October 26, 1998. Table of Contents. 16.1. Mass Loss by the Sun and Stars. 16.1.1. The Solar Wind. 16.1.2. Mass Loss by Stellar http://www.physics.gmu.edu/classinfo/astr103/CourseNotes/ECText/ch16_txt.htm

Astronomy Supplement 16. The Interstellar Medium Latest Modification: October 26, 1998 Table of Contents 16.1. Mass Loss by the Sun and Stars 16.1.1. The Solar Wind 16.1.2. Mass Loss by Stellar Winds 16.2. Explosive Variable Stars 16.2.1. Planetary Nebulae 16.2.2. Novae 16.2.3. Supernovae Box 16.1. - The Crab Nebula and Pulsar 16.3. Interstellar Matter 16.3.1. Interstellar Gas 16.3.2. The 21-CM Line Biography - Karl Guthe Jansky (1905-1950) 16.3.3. Interstellar Molecules 16.3.4. Interstellar Dust 16.4. Interstellar Clouds 16.4.1. Diffuse and Dark Clouds 16.4.2. Obscuring Effect of Interstellar Clouds 16.4.3. Carbon Monoxide in Dark Clouds 16.4.4. Interstellar Masers, Dark Clouds with Energy Sources 16.5. Emission Nebulae 16.5.1. H II Regions 16.5.2. What Type of Interstellar Medium Surrounds the Sun? If you exhale your breath once and let it expand into an evacuated cubical enclosure 1 kilometer on a side, the resulting density of your breath will exceed the density in most parts of the interstellar medium. Although this suggests that interstellar space is nearly a vacuum, there is a significant amount of matter lying between the stars because of the vast volume of space. Interstellar matter is primarily a gas, in which hydrogen is the chief component. In regions near very luminous, hot stars the gas is ionized, whereas in other regions it is so cold that molecules exist in it. Thus the interstellar medium is far from uniform in its properties. Mixed with the interstellar gas is a very fine dust, whose grains are about the size of the particles that are seen as small flashes in a shaft of light coming through a window. Interstellar dust, however, has a very different chemical composition and origin than particles of Earth dust.

5. The Interstellar Medium (ISM) The interstellar medium (ISM). The interstellar medium represents theraw material for forming future generations of stars. Nebulae. http://pegasus.phast.umass.edu/a100/handouts/ism.html

The Interstellar Medium (ISM) Gas and Dust between the stars accounts for 2030% of the mass of our Galaxy. Much of this material has been ejected by old and dying stars 99% of the ISM is gas mostly Hydrogen about one atom per cubic centimeter 1% is in microscopic (about 1 micron diameter) dust grains. Composition: silicates, carbon, or ice about one grain per cubic football field The interstellar medium represents the raw material for forming future generations of stars. Nebulae The distribution of the ISM is ``clumpy". Dark Clouds Dust blocks distant stars from view. Reflection Nebulae Nearby stars illuminate a dust cloud. Emission Nebulae (HII regions) Hot nearby stars ionize gas causing it to glow. Most of the light comes from the discrete spectral lines of the elements. Created March 28, 1996

6. Astronomy HyperText Book: Interstellar Medium Much Still Under Development. The interstellar medium (ISM) is the stuffbetween the stars. Most of this stuff consists of gas and dust . 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

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 rest is ``dust''. The interstellar medium affects starlight and stars (and 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''. The interstellar medium affects starlight and stars (and planets) form from clouds in the interstellar medium, so it is worthy of study. Also, the structure of the Galaxy is mapped from measurements of the gas. Dust The dust is made of thin, highly flattened flakes or needles of graphite (carbon) and silicates (rock-like minerals) coated with water ice. Each dust flake is roughly the size of the wavelength of blue light or smaller. The dust is probably formed in the cool outer layers of red giant stars and dispersed in the red giant winds and planetary nebulae.

8. ADC Quick Reference Interstellar Medium (ISM) ADC Quick Reference Page interstellar medium (ISM) in our GALAXY used ADC dataset holdings regarding the interstellar medium (ISM). The references listed here constitute only http://adc.gsfc.nasa.gov/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)

9. Lecture: Interstellar Medium Astronomy 124. The interstellar medium This material is collectively known as the interstellar medium the material between the stars the room has about 1019 atoms in it. The interstellar medium is not uniform in density 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

10. What Is The Interstellar Medium? Simply put, the interstellar medium is the material which fills thespace between the stars. Many people imagine outer space to http://www-ssg.sr.unh.edu/tof/Outreach/Interstellar/what1.html

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: Cold clouds of neutral atomic or molecular hydrogen; and

11. University Of Massachusetts - High Energy Astrophysics Group Research group primarily interested in high energy activities in galaxies, particularly the interplay between massive stars and the interstellar medium. http://www.astro.umass.edu/ast_page/xray/heag.html

12. MOST: Canada's First Space Telescope Detection and characterisation of (1) acoustic oscillations in Sunlike stars, including very old stars (metal-poor subdwarfs) and magnetic stars (roAp), to probe seismically their structures and ages; (2) reflected light from giant exoplanets closely orbiting Sun-like stars, to reveal their sizes and atmospheric compositions; and (3) turbulent variations in massive evolved (Wolf-Rayet) stars to understand how they add gas to the interstellar medium. http://www.astro.ubc.ca/MOST/

MOST RECENT NEWS May 2004 MOST continues to function beautifully. We are preparing to make the first public announcement of MOST scientific results within a few weeks. Please stay tuned to this site for news in the near future. PARTNERS MOST is a suitcase-sized (65 cm x 65 cm x 30 cm, 60 kg) microsatellite designed to probe stars and extrasolar planets by measuring tiny light variations undetectable from Earth. This can be done with such a small telescope (15 cm aperture) thanks to new Canadian attitude control technology. MOST - un microsatellite de la taille d'une mallette (65 cm x 65 cm x 30 cm, 60 kg), explorera étoiles et planètes extrasolaires en mesurant d'infimes variations de lumière indétectables depuis la Terre. L'utilisation d'un télescope de si petite taille (ouverture de 15 cm) est rendue possible grâce à la nouvelle technologie canadienne de commande d'attitude de satellites. FastCounter by bCentral

13. The Interstellar Medium: A Tutorial Although the subject may sound. INTIMIDATING It does not have to be. Begin here with the basics After you have learned the basics, move on to http://www-ssg.sr.unh.edu/tof/Outreach/Interstellar/home.html

Although the subject may sound INTIMIDATING... It does not have to be. Begin here with the basics: After you have learned the basics, move on to...

14. LAPD Plasma Physics Lab UCLA facility conducting basic plasma physics research on the behavior of naturally occurring plasmas, such as the auroral ionosphere, the magnetosphere, the solar wind, the solar corona, and the interstellar medium. http://128.97.43.7/lapd/

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15. The Astronomical Journal Founded in 1849 and published by the American Astronomical Society with an emphasis on observational papers. Its expanded coverage of quasars, galaxies, supernova remnants, and studies of the interstellar medium complements the more traditional areas of astronomy, including galactic structure and dynamics, astrometry, variable and binary stars, solar system studies, and cosmology. http://www.journals.uchicago.edu/AJ/home.html

Editor: Paul Hodge Sponsor: American Astronomical Society ISSN: 0004-6256 The Astronomical Journal Electronic Edition Editorial Office Home Page, Seattle Journal Description Information about Electronic Subscriptions List of Institutions Currently Registered Letter to Institutional Subscribers Registration Form Institutional Site License ... Letter, Registration Form, and Site License (PDF) Editorial Board Information for Authors General Instructions to Authors Electronic Submission Guidelines Key Words IAU Recommendations for Nomenclature ... 2004 Page Charge Authorization Form (PDF) 2003 Page Charges (PDF) Publication Agreement Form (PDF) Preparation of Word and WordPerfect Manuscripts General Instructions Special Instructions for Tables Special Instructions for Math How to Subscribe to ... AJ Order Single Articles or Back Issues AAS Centennial Volume (PDF) Review Of Related Interest from the University of Chicago Press Contact the Editorial Office Subscription Center ... Journals Division

16. METEORITICS & PLANETARY SCIENCE Journal Of The Meteoritical Society The journal of The Meteoritical Society. Topics include asteroids, comets, craters, interplanetary dust, interstellar medium, lunar samples, meteors, meteorites, natural satellites, planets, tektites, and origin and history of the solar system. http://cavern.uark.edu/~meteor/

New Editor for 2003 Current issue cover Upcoming meetings Editorials (Table of contents service) Abstracts and Table of Contents Free preview of electronic issues For subscribers only (Electronic service) Electronic Issues Categories of Papers Published Information for ... Contributors • Submitting a manuscript • Submitting a review Notes for Associate Editors Editor Associate Editors ... Enter here M P LANETARY S CIENCE The Journal of the Meteoritical Society THE CENTRAL FORUM FOR RESEARCH IN PLANETARY SCIENCE: The journal publishes invited reviews surveying major topics in planetary science, research articles describing the results of major new studies, editorials on topics of current interest and book reviews. MAPS brings together professional scientists from a variety of backgrounds and disciplines including astronomy, chemistry, geology, physics, and biology. THE LATEST RESEARCH: is published monthly. It is available in hard copy and on-line. 75% of accepted articles are in print within six months of submission. Starting January 1, 2003 all journal operations will be under

17. Interstellar Medium: Cold interstellar medium When one Neutral Hydrogen Most of the interstellarmedium is in the form of neutral hydrogen gas (HI). The typical http://zebu.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.

18. Sterrewacht Leiden | Leiden Observatory - Welcome Research focuses on a number of different areas covering astronomical interests which range from the study of stars and the interstellar medium to galaxies and the largescale structure of the universe. http://www.strw.leidenuniv.nl/

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19. Stars - Interstellar Medium Stars interstellar medium. 4/2/98. Click here to start. Table of Contents.Stars - interstellar medium. interstellar medium Defined. PPT Slide. http://www.physics.gmu.edu/classinfo/astr103/CourseNotes/Ppt/Lec04_pt7_interstel

Stars - Interstellar Medium Click here to start Table of Contents Stars - Interstellar Medium Interstellar Medium Defined PPT Slide Physical Constituents Of IM ... Coronal Gas Regions Author: J. C. Evans Email: jevans@gmu.edu

20. Interstellar Medium interstellar medium. interstellar medium (ISM). Index. Stuff between the stars.1015% of the visible mass of the Galaxy. 99% of the ISM mass is gas; 1% dust. 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

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