Solar interstellar neighborhood

solar neighborhood definition and solar system neighborhood
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Prof.EvanBaros,United Kingdom,Teacher
Published Date:26-07-2017
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Chapter 17 Measuring the StarsUnits of Chapter 17 17.1 The Solar Neighborhood XXNaming the Stars 17.2 Luminosity and Apparent Brightness 17.3 Stellar Temperatures XXMore on the Magnitude Scale 17.4 Stellar Sizes Estimating Stellar Radii 17.5 The Hertzsprung-Russell DiagramUnits of Chapter 17 (cont.) 17.6 Extending the Cosmic Distance Scale 17.7 Stellar Masses XXMeasuring Stellar Masses in Binary Stars 17.8 Mass and Other Stellar Properties17.1 The Solar Neighborhood Remember that stellar distances can be measured using parallax:17.1 The Solar Neighborhood Nearest star to the Sun: Proxima Centauri, which is a member of the three-star system Alpha Centauri complex Model of distances: Sun is a marble, Earth is a grain of sand orbiting 1 m away Nearest star is another marble 270 km away Solar system extends about 50 m from Sun; rest of distance to nearest star is basically empty17.1 The Solar Neighborhood The 30 closest stars to the Sun:17.1 The Solar Neighborhood Next nearest neighbor: Barnard’s Star Barnard’s Star has the largest proper motion of any star—proper motion is the actual shift of the star in the sky, after correcting for parallax These pictures were taken 22 years apart:17.1 The Solar Neighborhood Actual motion of the Alpha Centauri complex:17.2 Luminosity and Apparent Brightness Luminosity, or absolute brightness, is a measure of the total power radiated by a star. Apparent brightness is how bright a star appears when viewed from Earth; it depends on the absolute brightness but also on the distance of the star:17.2 Luminosity and Apparent Brightness Therefore, two stars that appear equally bright might be a closer, dimmer star and a farther, brighter one:17.2 Luminosity and Apparent Brightness Apparent luminosity is measured using a magnitude scale, which is related to our perception. It is a logarithmic scale; a change of 5 in magnitude corresponds to a change of a factor of 100 in apparent brightness. It is also inverted—larger magnitudes are dimmer.17.2 Luminosity and Apparent Brightness If we know a star’s apparent brightness and its distance from us, we can calculate its absolute luminosity.17.3 Stellar Temperatures Recall Wein’s Law for blackbodies: The color of a star is indicative of its temperature. Red stars are relatively cool, while blue ones are hotter.17.3 Stellar Temperatures The radiation from stars is approximately blackbody radiation; as the blackbody curve is not symmetric, observations at two wavelengths are enough to define the temperature. The relative amount of light in two wavelength bands is an object’s color.17.3 Stellar Temperatures Stellar spectra are much more informative than the blackbody curves (continuous part of the spectrum). There are seven general categories of stellar spectra, corresponding to different temperatures. From highest to lowest, those categories are: O B A F G K M17.3 Stellar Temperatures Here are their spectra:17.3 Stellar Temperatures Characteristics of the spectral classifications:17.4 Stellar Sizes A few very large, very close stars can be imaged directly using speckle interferometry. This is Betelgeuse.17.4 Stellar Sizes For the vast majority of stars that cannot be imaged directly, size must be calculated knowing the luminosity and temperature: • Giant stars have radii between 10 and 100 times the Sun’s • Dwarf stars have radii equal to, or less than, the Sun’s • Supergiant stars have radii more than 100 times the Sun’s17.4 Stellar Sizes Stellar radii vary widely:

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