The practical astronomer : comprising illustrations of light and colours, practical descriptions of all kinds of telescopes, the use of the equatorial-transit, circular, and other astronomical instruments, a particular account of the Earl of Rosse's large telescopes, and other topics connected with astronomy (1845)
Dick, Thomas, 1774-1857 · London : Seeley, Burnside, and Seeley · leaf 231
nature. 206 THE PRACTICAL ASTRONOMER. CHAPTER III. ON THE OPTICAL ANGLE, AND THE APPARENTMAGNITUDE OF OBJECTS. In order to understand the principle on whichtelescopes represent distant objects as magnified,it may be expedient to explain what is meant bythe angle of vision, and the apparent… … an object to the eye. Thus AEB or CED (fig.40.) is the optical or visual angle, or the angleunder which the object AB or CD, appears to theeye at E. These two objects, being at differentdistances, are seen under the same angle, althoughCD is evidently larger than AB. On the retina THE OPTICAL…
Astronomy · Astronomical instruments · Telescopes
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