# Introduction to Stellar Astrophysics: Basic stellar by Erika Böhm-Vitense

By Erika Böhm-Vitense

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Introduction to Stellar Astrophysics: Basic stellar observations and data

This textbook advent to the fundamental components of primary astronomy and astrophysics serves as a starting place for figuring out the constitution, evolution, and saw homes of stars. the 1st 1/2 the booklet explains how stellar motions, distances, luminosities, colours, radii, lots and temperatures are measured or derived.

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They also seem to follow one curve, which is, however, different from the one for black bodies, but still all stars with a given color B — V have nearly the same U — B color. Both colors are determined by one parameter, which we still suspect to be the temperature. Before we can, however, establish a relation between the colors of a star and its temperature we have to understand the difference between the stellar energy distributions and those of black bodies, and especially why the stars have so much less energy in the U band than the black bodies.

2), if we measure the angular radius in radians. It is important to notice that it is often easier to determine nF the surface flux on the star than it is to determine the luminosity, because for Fig. 2. The ratio R/d is the angular radius of the star as measured by the observer at distance d. A pencil piece of length s at a distance / from the observer covers the diameter of the sun. The ratio s/l can easily be measured, and equals 2R/d. 2 The luminosity of the sun 43 stars not too distant it is easier to measure the angular diameter than it is to measure their distance.

7) In Fig. 8 we show the wavelength dependence of the intensities emitted by black bodies of different temperatures. Of course, we cannot make black bodies with temperatures of 6000 K in the laboratory because any box of any kind of material would melt at such temperatures, but we can derive the law for the intensity distribution from measurements for lower temperatures and then use this law to calculate what the energy distribution for higher temperatures will look like. You will recall that it was the observed law for the radiation of a black body which led Max Planck to the discovery of the light quanta.