Hertzsprung-Russell diagram

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Posts: 131433

Date: Feb 7 01:24 2013

RE: Hertzsprung-Russell diagram	Permalink

Title: The Critical Importance of Russell's Diagram Authors: Owen Gingerich The idea of dwarf and giants stars, but not the nomenclature, was first established by Eijnar Hertzsprung in 1905; his first diagrams in support appeared in 1911. In 1913 Henry Norris Russell could demonstrate the effect far more strikingly because he measured the parallaxes of many stars at Cambridge, and could plot absolute magnitude against spectral type for many points. The general concept of dwarf and giant stars was essential in the galactic structure work of Harlow Shapley, Russell's first graduate student. In order to calibrate the period-luminosity relation of Cepheid variables, he was obliged to fall back on statistical parallax using only 11 Cepheids, a very sparse sample. Here the insight provided by the Russell diagram became critical. The presence of yellow K giant stars in globular clusters credentialed his calibration of the period-luminosity relation by showing that the calibrated luminosity of the Cepheids was comparable to the luminosity of the K giants. It is well known that in 1920 Shapley did not believe in the cosmological distances of Heber Curtis' spiral nebulae. It is not so well known that in 1920 Curtis' plot of the period-luminosity relation suggests that he didn't believe it was a physical relation and also he failed to appreciate the significance of the Russell diagram for understanding the large size of the Milky Way. Read more (2056kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Aug 3 18:07 2011

Age of Stars	Permalink

Rotation Rate Could Pin Down Age of Stars Stars of the sky play a bit coy with their ages - an ancient star can often pass for a much younger one. That is a problem for astronomers seeking out habitable planets orbiting distant stars because a star's age correlates with the life-forms it could support. Read more __________________

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Posts: 131433

Date: May 23 21:15 2011

Star's Age	Permalink

How to Learn a Star's True Age Like our Sun, most stars look almost the same for most of their lives. So how can we tell if a star is one billion or 10 billion years old? Astronomers may have found a solution - measuring the star's spin. "A star's rotation slows down steadily with time, like a top spinning on a table, and can be used as a clock to determine its age" - Astronomer Soren Meibom of the Harvard-Smithsonian Center for Astrophysics. Meibom presented his findings today in a press conference at the 218th meeting of the American Astronomical Society. Read more __________________

Blobrana

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Posts: 131433

Date: Nov 13 01:36 2009

Henyey track	Permalink

The Henyey track is a path taken by pre-main sequence stars with masses >0.5 Solar mass in the Hertzsprung-Russell diagram after the end of Hayashi track. Read more __________________

Blobrana

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Posts: 131433

Date: Nov 13 01:34 2009

Hayashi track	Permalink

The Hayashi track is a path taken by protostars in the Hertzsprung-Russell diagram after the protostellar cloud has reached approximate hydrostatic equilibrium. Read more __________________

Blobrana

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Posts: 131433

Date: Oct 20 23:25 2009

RE: Hertzsprung-Russell diagram	Permalink

Chapter 11G HR Diagrams Click to Play \| View Details __________________

Blobrana

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Posts: 131433

Date: Oct 15 00:37 2009

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HertzsprungRussell diagram Click to Play \| View Details __________________

Blobrana

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Posts: 131433

Date: Sep 19 15:32 2009

Star Colours	Permalink

At first, it seems that when you look up at the night sky, everything is white against a dark background. However, within a few minutes, an observer will start to notice that some of the stars have a different tinge to them. Blue, yellow, and red stars begin to stand out against the dark sky. Backyard astronomers can often point out one or two red stars in the sky, but that colour is not abundant. It is estimated that only about 150 stars can be identified with the naked eye as having a colour other than white. Also, only about 30 of those could be considered distinctive. Read more __________________

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Posts: 131433

Date: Apr 16 17:58 2009

RE: Hertzsprung-Russell diagram	Permalink

For astronomers, stars are as individual as people, each exhibiting different characteristics and qualities. "As we study stars, we are understanding that they are as individual as human beings. While the traditional classification system of stars was limited to temperature and luminosity, we are realizing that there are so many other ways that stars can vary and be individuals" - Richard O. Gray, a professor of astronomy at Appalachian State University and the author of a new book on stellar classification. Read more __________________

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Date: Apr 9 19:53 2009

Stellar Spectral Classification	Permalink

For astronomers, stars are as individual as people, each exhibiting different characteristics and qualities. "As we study stars, we are understanding that they are as individual as human beings. While the traditional classification system of stars was limited to temperature and luminosity, we are realising that there are so many other ways that stars can vary and be individuals" - Richard O. Gray, a professor of astronomy at Appalachian State University. For instance, astronomers have discovered that some stars have enhanced abundances of various chemical elements, such as carbon, barium or silicon. "There are many other sorts of peculiarities. Stellar astronomers are interested in studying peculiar stars as a way to understand normal stars" - Richard O. Gray. Gray uses a spectrograph to analyse the spectra of stars. He specialises in stellar spectral classification, and is the lead author of the newly released "Stellar Spectral Classification" published by Princeton University Press. The text, coauthored with Christopher J. Corbally, replaces a decades-old book on spectral classification still in use in many college classrooms and observatories. Read more __________________

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