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Topic: Galaxy classification

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	Galaxy - Wikipedia, the free encyclopedia
		Most galaxies are several thousand to several hundred thousand light years in diameter and are usually separated from one another by distances on the order of millions of light years.
		Clusters of galaxies are often dominated by a single giant elliptical galaxy, which over time tidally destroys its satellite galaxies and adds their mass to its own.
		The galaxy will continue to absorb infalling material from high velocity clouds and dwarf galaxies throughout its life; the cycle of stellar birth and death will increase the abundance of heavy elements, eventually allowing the formation of planets.
	en.wikipedia.org /wiki/Galaxy (2508 words)

	Galaxy classification - Wikipedia, the free encyclopedia
		Astronomers classify galaxies based on their overall shape (elliptical, spiral or barred spiral) and further by the specific properties of the individual galaxy (for example degree of ellipse, number of spirals or definition of bar).
		From this, astronomers have constructed a theory of galaxy evolution which suggests that ellipticals are, in fact, the result of collisions between spiral and/or irregular galaxies, which strip out much of the gas and dust and randomize the orbits of the stars.
		Galaxies and the Universe - an introduction to galaxy classification
	en.wikipedia.org /wiki/Galaxy_classification (1031 words)

	galaxy classification
		Devised by Edwin Hubble, it splits galaxies into ellipticals, spirals (normal and barred), and irregulars, and is represented by the familiar tuning-fork diagram.
		Galaxies are often said to be "early" (E and S0) or "late" (Sb,Sc, Irr) in type, a remnant of early notions that galaxies physically evolve along the Hubble sequence.
		DDO (or van den Bergh) classification of galaxies
	www.daviddarling.info /encyclopedia/G/galaxy_classification.html (446 words)

	Encyclopedia :: encyclopedia : Scientific classification (Site not responding. Last check: 2007-10-23)
		Advances in classification due to the work of entomologists and the first microscopists is due to the research of people like Marcello Malpighi (1628–1694), Jan Swammerdam (1637–1680), and Robert Hooke (1635–1702).
		The approach he took to the classification of plants in his Historia Plantarum was an important step towards modern taxonomy.
		The usual classifications of five species follow: the fruit fly so familiar in genetics laboratories (Drosophila melanogaster), humans (Homo sapiens), the peas used by Gregor Mendel in his discovery of genetics (Pisum sativum), the fly agaric mushroom Amanita muscaria, and the bacterium Escherichia coli.
	www.hallencyclopedia.com /Scientific_classification (1028 words)

	Lenticular galaxy - Wikipedia, the free encyclopedia
		The Spindle Galaxy (NGC 5866), a lenticular galaxy in the Draco constellation.
		A lenticular galaxy is a type of galaxy which is an intermediate between an elliptical galaxy and a spiral galaxy in the Hubble sequence classification scheme.
		Lenticular galaxies are disc galaxies (like spiral galaxies) which have used up or lost their interstellar matter (like elliptical galaxies).
	en.wikipedia.org /wiki/Lenticular_galaxy (130 words)

	Galaxy
		Although so-called dark matter appears to account around 90% of the mass of most galaxies, the nature of this unseen components is not well understood.
		NGC 250 is a result of two spiral galaxies colliding, in a fashion similar to that expected for the Andromeda and Milky Way.
		Eventually, as a result of gravitational relaxation, eventually all stars will either fall into the central supermassive fl hole of the galaxies, or be flung into the depths of intergalactic space as a result of collisions.
	www.brainyencyclopedia.com /encyclopedia/g/ga/galaxy.html (2431 words)

	Types of galaxies
		Galaxies of this class have smoothly varying brightnesses, with the degree of brightness steadily decreasing outward from the centre.
		These galaxies are conspicuous for their spiral-shaped arms, which emanate from or near the nucleus and gradually wind outward to the edge.
		Galaxies of the fifth subtype, in particular, tend to be intrinsically faint, while those of the first subtype are among the most luminous spirals known.
	www.wiedenhoff.nu /galaxy/galax2.htm (2704 words)

	Galaxies and the Universe - Galaxy Classification
		Galaxy classification has developed with this aim, from rough description of an image through distinctions among components with different astrophysical properties.
		Galaxies are often called early (E and S0) or late (Sb,Sc, Irr) in type, a remnant of early notions that galaxies physically evolve along the Hubble sequence.
		Classifications of this kind, based on light concentration, have received renewed interest in the context of high-redshift galaxies, and with the recognition that they can be made robust even for poorly resolved systems by appropriate modelling.
	www.astr.ua.edu /keel/galaxies/classify.html (2800 words)

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		Galaxies are fundamental units of matter in space, and determining how they formed and achieved their current state is of critical importance to many issues in astronomy.
		Although galaxy morphology presents problems for classification that would not be encountered in biological taxonomy, visual galaxy classification continues to be useful at a time when galaxies have never been better understood.
		Galaxies at extremely large distances (several billion light years, where 1 light year is the distance light travels in one year) are being seen as they were when the Universe was considerably younger than it is now.
	bama.ua.edu /~rbuta/gvatlas/intro.html (1019 words)

	The Hubble Classification (Site not responding. Last check: 2007-10-23)
		Galaxies may be viewed as the basic building blocks for the large-scale visible stucture of the Universe.
		Hubble introduced the classification scheme illustrated in the following figure, which separates most galaxies into elliptical, normal spiral, and barred spiral categories, and then sub-classifies these categories with respect to properties such as the amount of flattening for elliptical galaxies and the nature of the arms for spiral galaxies.
		This diagram is termed the Hubble classification scheme, or (because of its shape) the "tuning fork diagram".
	csep10.phys.utk.edu /astr162/lect/galaxies/hubble.html (158 words)

	Galaxy Classification Lab - Astro 113 - Matthew A. Bershady
		Galaxies are some of the most beautiful and intriguing objects in the night sky.
		Some astronomers have realized that categorizing galaxies by their spectra, as was done for stars, might provide an alternative, and possibly more quantitative and physically insightful method of classification.
		Since no two galaxies are identical, when you classify other galaxies by comparing them to your reference sequence, you will have to estimate whether they are closer to one 'type' or another.
	www.astro.wisc.edu /~mab/education/astro113/galclass_lab.html (2607 words)

	Galaxy Classification
		Galaxies are aggregates of gas, dust and millions (sometimes even billions or trillions) of stars held together by mutual gravitational forces.
		Elliptical galaxies, also known as Type E Galaxies, range in shape from E0, which is almost spherical, to E7, which is highly elongated.
		Barred spiral galaxies, also known as Type SB galaxies, are a sub division of spiral galaxies and have a bar of stars and intersteller matter running through their nuclei.
	www.users.zetnet.co.uk /pete/Galaxieshtm.htm (257 words)

	Hubble Galaxy Classification
		Disc galaxies have a bulge in the centre, which is very similar to an elliptical galaxy, but outside of that they have a thin disc of stars.
		However, because galaxies are randomly oriented relative to our line of sight, we see most of them tilted, giving them a more or less elliptical shape in the sky, somewhere between face-on and edge-on.
		Hubble originally arranged the different shapes of galaxy in the form of a tuning fork, because he noticed a gradual variation in visual appearance between the different galaxies that he observed.
	www.faulkes-telescope.com /index.php?page=74 (795 words)

	HOU Galaxy Workshop - Galaxy Types (Site not responding. Last check: 2007-10-23)
		Galaxies are classified in different types based on their structure and appearance in the sky.
		Edge-On Spiral Galaxies and Face-On Spiral Galaxies are the same type of galaxy but the name depends on their orientation in the sky.
		Below are examples of an edge-on spiral galaxy, a face-on spiral galaxy, and an elliptical galaxy.
	hou.lbl.gov /ISE/new/galaxy/galaxy2.html (235 words)

	Star/galaxy classification for Sloan Digital Sky Survey (Site not responding. Last check: 2007-10-23)
		This project is being executed under the auspices of the Astrophysical Research Consortium by researchers at the University of Chicago, Fermi National Accelerator Laboratory, the Institute for Advanced Study, Johns Hopkins University, the National Observatory of Japan, and Princeton University.
		Stars, galaxies and quasars in the photometric images need to be separated from each other, and from the various types of noise.
		We were able to build small decision tree classifiers for discriminating very accurately between star and galaxy images, down to the detection limit of the survey.
	www.tigr.org /~salzberg/murthy_thesis/node47.html (392 words)

	CLASSIFICATION (Site not responding. Last check: 2007-10-23)
		Elliptical galaxies are given a classification that corresponds to their elongation from a perfect circle, otherwise known as their ellipticity.
		The larger the number, the more elliptical the galaxy is. So, for example a galaxy of classification of E0 appears to be perfectly circular, while a classification of E7 is very flattened.
		The halo of a galaxy is a loose, spherical structure located around the bulge and some of the disk.
	astrosun.tn.cornell.edu /academics/courses/astro201/galaxies/types.htm (497 words)

	PH308 --- Galaxy Classification (Site not responding. Last check: 2007-10-23)
		External galaxies occur in a wide variety of shapes and sizes.
		Galaxies on the left of this diagram are designated "early types," and those toward the right are called "late types." These labels arise because Hubble believed that this diagram represents and evolutionary sequence.
		One further sub-class of galaxy worth mentioning is the low surface brightness (LSB) type.
	bustard.phys.nd.edu /PH308/galaxies/classification.html (199 words)

	[No title]
		The subtle morphological differences between the two galaxies in the upper panels and the two in the lower panels are highlighted with the notation in Figure 1.
		De Vaucouleurs was keenly interested in van den Bergh luminosity classifications, and spent considerable effort in evaluating systematic effects in such classifications for use in distance scale research.
		Galaxies later known as ``flocculent'' spirals by Elmegreen and Elmegreen (1987) were denoted high multiplicity, filamentary spirals by de Vaucouleurs (1956).
	bama.ua.edu /~rbuta/gvatlas/plan.html (2044 words)

	Galaxy Morphology and Classification - Cambridge University Press
		The classification of galaxies according to their shape is a fundamental tool in astronomy.
		It is through classification schemes that astronomers build a deeper understanding of how galaxies form and evolve.
		This is the first book dedicated entirely to the shapes and classifications of galaxies.
	www.cambridge.org /catalogue/catalogue.asp?isbn=0521623359 (408 words)

	Galaxy Classification Lab
		In the 1920's, astronomers came to understand that some of these nebulosities are actually galaxies -- systems of tens, hundreds, or even thousands of billions of stars (and interstellar gas and dust) organized by their common gravitational field.
		Almost all galaxies are so incredibly distant that they are too faint to be seen with the naked eye (the Large and Small Magallenic Clouds and the Andromeda Galaxy are the only three exceptions).
		Be sure to note the description of sub-classifications such as the presence of bars in spiral galaxies or the elongation of elliptical galaxies.
	www.wku.edu /~mike.carini/astro/galclass.htm (578 words)

	Spiral Galaxy Classification (Site not responding. Last check: 2007-10-23)
		Spiral galaxies are classified in categories based on the appearance of a number of their features.
		In terms of the size of the central bulge, Sa galaxies have the largest nuclear bulge, while Sc galaxies have the smallest nuclear bulge.
		Sa galaxies have less gas and dust than the average spiral galaxy, while Sc galaxies have more gas and dust than the average galaxy.
	www.astro.psu.edu /~stm/f05/astro1/inclass/spirals.html (107 words)

	Untitled Page (Site not responding. Last check: 2007-10-23)
		An Sa would be a galaxy with a large bulge and tightly wrapped arms and an SBc would have a small, oval bulge with arms that attach to the end of the bar and spread out away from the center.
		In many cases he classified galaxies as peculiar because there was an unresolved companion, so it looked like there was a blob on the side of the galaxy.
		He basically expanded the Hubble classification system allowing for inermediate classes such as Sab, and adding extra notations such as + and - signs or extra letters like m to indicate things like the the strength of the bar, disk structure in lenticulars, rings in sprirals, and different structures in irregulars.
	www.astro.lsa.umich.edu /Course/Labs/GalClass/GalClass.html (1853 words)

	NSO: Astronomy: Galaxy Classification (Site not responding. Last check: 2007-10-23)
		These galaxies are very thin and almost disappear when seen from the edge.
		Very like a spiral galaxy, but the "arms" are not stuck right onto the "bulge" but to the ends of a bar through the middle.
		A small number of galaxies do not look like any of the other types.
	www.schoolsobservatory.org.uk /astro/textb/gals/class.htm (94 words)

	CERES: Galaxy Classification Activity
		In this inquiry activity, students view NASA images of galaxies and develop a galaxy classification scheme.
		Your first task is to sort the galaxies by creating and applying a classification scheme based on appearance.
		Billions of galaxies, each a gravitationally bound cluster of billions of stars, now form most of the visible mass in the universe.
	btc.montana.edu /ceres/html/Galaxy/gal1.html (319 words)

	skeleton
		However, it must be emphasized that many classification schemes were based on only the brightest, highest-surface-brightness galaxies at the time, so included only the intrinsically most luminous systems and the nearest systems.
		Even today galaxy classification is incomplete for the lowest-L systems like dwarf galaxies and the LSB (low-surface-brightness) galaxies, due to the difficulty in detecting these galaxies, and their subsequent lack of appropriate representation in galaxy catalogs (although many studies are trying to rectify this!)
		There are numerous other classification schemes and modifications to the Hubble sequence (the Sd - Im classifications were fully added by de Vaucouleurs in 1959) which all cannot be mentioned here.
	www.astro.ubc.ca /people/durrell/a303/classification.html (609 words)

	Star/galaxy classification (Site not responding. Last check: 2007-10-23)
		A perfect PSF would be given a star/galaxy (s/g) classification of 1.0, while a significantly extended source would be given a classification of 0.0.
		The first 2 models in figure 5.9 illustrate the case for a quasar population that decreases exponentially beyond a redshift of 2.7 (solid line), and one that stays constant out to an exponential cut-off at z = 5 (dashed line).
		It therefore appears likely that most of the unclassified objects are also actually galaxies.
	www.roe.ac.uk /~jcm/thesis/node71.html (551 words)

	Open Directory - Science: Astronomy: Galaxies (Site not responding. Last check: 2007-10-23)
		Complete Spiral Galaxy Pictures Gallery - Contains over 600 pictures of all spiral galaxies larger than 3 minutes of arc for all constellations in the Northern and Southern celestial hemispheres.
		European Network: The Formation and Evolution of Galaxies - Purpose is to understand the creation of galaxies and the universe has evolved.
		Galaxies - Some useful information about kinds of galaxies, content of galaxies, clusters of galaxies, galaxies and cosmology.
	dmoz.org /Science/Astronomy/Galaxies (531 words)

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