. The Adolfo Stahl lectures in astronomy, delivered in San Francisco, California, in 1916-17 and 1917-18, under the auspices of the Astronomical Society of the Pacific. andle-power alone, we can conclude nothing as to theextent of the luminous surface emitting the light seen by anobserver on the mountain. 12. Relation of Color to Magnitude •«? We have referred to the fact that the spectrum of a star isnot an exact measure of its color, and that objects having thesame type of spectrum may show appreciable differences incolor. Investigations by several observers have shown thatthese di
. The Adolfo Stahl lectures in astronomy, delivered in San Francisco, California, in 1916-17 and 1917-18, under the auspices of the Astronomical Society of the Pacific. andle-power alone, we can conclude nothing as to theextent of the luminous surface emitting the light seen by anobserver on the mountain. 12. Relation of Color to Magnitude •«? We have referred to the fact that the spectrum of a star isnot an exact measure of its color, and that objects having thesame type of spectrum may show appreciable differences incolor. Investigations by several observers have shown thatthese differences are related to the absolute magnitudes of thestars, the more luminous objects being the redder. Determinations of the exposure ratio for a group of giantand dwarf stars illustrate the nature of the dependence. The 234 The Adolfo Stahl Lectures results are illustrated in Fig. 20, in which vertical distancesrepresent the logarithm of the exposure ratio, while horizontaldistances correspond to spectral types. The circles indicategiant stars and the points dwarfs. The dotted line gives thevariation in the logarithm of the exposure ratio for the colors. Fig. 20. Variation of Color With Spectrum for Giant (HeavyLine) and Dwarf (Light Line) Stars. Vertical distances representlogarithms of the ratio of exposure for blue light to exposure foryellow light necessary to produce the same photographic effect. Forstars having G and K spectra the giants are appreciably redder thanthe dwarfs. normally assumed, in the Mount Wilson color system, tocorrespond to the different spectral types, and was derivedfrom the color indices and spectra of the Polar Standards ofmagnitude. None of the giants differs greatly from zero abso-lute magnitude, and the progession of exposure ratio withspectrum for these stars is fairly regular. The dwarf starsaverage 4 or 5 magnitudes fainter than the giants, andalthough the scattering of the points is considerable, thechange in the exposure ratio with sp
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectastronomy, bookyear19
