Man's physical universe

xanabras

UNIT II

SECTION 3

MANY INSTRUMENTS SUPPLEMENT THE TELESCOPE

IN EXPLORING THE UNIVERSE

Introduction.

Nowhere is man's ingenuity shown to better advantage than in his

invention of instruments to aid him in making observations. In many

cases the information obtained requires interpretation in the Hght of

modern knowledge, and it is always possible that, as more knowledge

becomes available, these interpretations will have to be changed. It

is important, therefore, to keep in mind that the interpretations

presented in this section are in some cases several years old and it

quite possible that some of them now need revision.

The Camera Is More Sensitive Than the Eye.

By substituting a camera for the eye, the telescope becomes much

more useful, because it not only enables man to gather all of the light

from a star for many consecutive hours, but it provides a lasting record

which may be studied at leisure and be compared with similar photographs

taken from time to time.

The Spectrometer Is One of Man's Most Valuable Instruments.

To Newton we owe the discovery that light rays are bent when they

enter a prism, the visible and invisible rays forming a continuous

spectrum in which all of the rays originally present are separated. We

now know that the rays are separated because the rays of short wave

length are bent more than the rays of long wave length as they pass

through the prism. If red light rays are absent in the original light

rays, there will be a gap in the spectrum where red should occur, and

so on for all of the visible and invisible light rays. The invisible short

ultraviolet and long infrared rays, as well as the visible rays, may be

photographed, so that a camera generally replaces the eye in a spectrometer.

The spectrometer has two tubes, one of which collects a thin beam

of light through a narrow slit and renders the light parallel by means of

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