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NS READING NOtes

NS READING NOtes - 8:44:00 PM Chapter 17 I Intro Study of...

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14/04/2008 19:44:00 Chapter 17 I. Intro Study of stars began towards the end of the 18 th  century with the work of  William Herschel Herschel tried to find order among the stars o Began with observation and spent many years cataloging stars and  measuring their apparent motions I. Tools of Astronomy The Telescope o All modern ones are reflectors Telescope has always been the basic astronomical instrument Herschel was the first to build and use a large reflecting  telescope An instrument in which light is reflected from a concave  mirror instead of being refracted through a lens A number of individual mirrors are linked to produce a  single image Hexagonal mirror segments are used to give a  large collecting surface Or Separate circular mirrors are used o Advantages of Size The purpose of a big telescope is not magnification Stars are too far away to ever appear as more than  points of light Large mirrors and lenses have light-gathering power Enables more light from a given object to be collected
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Ability to distinguish – resolve —small details The diffraction of light waves causes every optical image  to be blurred to a certain extent The larger the lens or mirror, the less the blurring  and the sharper the image o Originally the light collected by a telescope went to the eye but  photographic plates were used and today electronic sensors are  preferred The latter methods have the advantage that they respond to the  total amount of light that falls on them over the period of time  they are exposed The eye can only respond to the brightness of the light that  reaches it The Spectrometer o Telescopes are limited when it comes to studying the stars o Combination of a telescope and a spectrometer are needed to see  stars o spectrometer  breaks light up into its separate wavelengths and the  resulting bands of color, with each wavelength separate from the  others, is the spectrum that is recorded on a photographic plate or  electronic medium Spectrum Analysis o Structure Absorption spectrum    a spectrum of dark lines on a  continuous colored background It is produced when light from a hot object passes  through a cooler gas Atoms and molecules of the gas absorb light of certain  wavelengths so leave narrow gaps in band of color o Temperature The temperature of a stars surface can be found in the  continuous background of a star’s spectrum
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Need to know where in the spectrum the stars radiation is  brightest Wavelength of maximum intensity decreases as the 
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