With the improvement of basing magnitudes on precise

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with the improvement of basing magnitudes on precise measurements of apparent or total luminosity rather than arbitrary and uncertain eye estimates of star brightness. That branch of observational astronomy which deals with the measurement of the intensity of starlight is called _______________. Explanation: Photometry. Sir William Herschel devised a simple and direct method of stellar photometry. His method depended on the fact that the light-gathering power of a telescope is proportional to the area of its lens. A more modern and accurate method of stellar photometry employs the visual photometer, a device attached to a telescope which produces an artificial star image. Looking through the telescope, the astronomer can vary the brightness and color of the artificial star to match the real star and discern the amount of energy provided to the artificial star image to accomplish this match. This is a measure of the luminous flux of the real star. The apparent brightness of a star can depend to some extent upon its ___________. Explanation: Color. Different colors produce different responses in the human eye. The eye is most sensitive to green and yellow light and has a lower sensitivity to the shorter wavelengths of blue and violet light and to the longer wavelengths of orange and red light. Photographic plates were devised to detect the light more accurately using color-sensitive photographic plates to filter the light to determine a more accurate magnitude of brightness. The colors of stars are determined by the distance and the temperature of the star. Below is an image of a star field in the region of Sagittarius showing stars of different colors: A perfect _____________ called a black body is an idealized body that completely absorbs all of the electromagnetic energy incident upon it. : Radiator. The star heats up until it reaches a temperature at which it emits radiation at exactly the same rate as it receives it, and then remains in equilibrium at that temperature. The ___________ emitted from black bodies is relative to the different wavelengths at different temperatures. Energy. A perfect radiator at any temperature emits some radiation at all wavelengths, but not in equal amounts. Note that a hotter black body emits more radiation at all wavelengths than does a cooler black body.
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However, the big difference is that a hotter black body emits the largest proportion of its energy at shorter wavelengths than a cooler black body does. Hot stars appear blue because most of their energy is at short wavelengths and cool stars appear red because most of their energy is at long wavelengths. The chart below shows the wavelengths of all types of energy, but in particular, note that orange and red are of long wavelengths, while violet and blue are of short wavelengths: A ____________ star is a double star or two stars revolving around each other.
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