Half-hours with the Telescope - Being a Popular Guide to the Use of the Telescope as a - Means of Amusement and Instruction. by Richard Anthony Proctor
page 85 of 115 (73%)
page 85 of 115 (73%)
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proper observation, however, the planet must be looked for with the
telescope in the manner above indicated, as he always shows a nearly semi-circular disc when he is visible to the naked eye. We come next to Venus, the most splendid of all the planets to the eye. In the telescope Venus disappoints the observer, however. Her intense lustre brings out every defect of the instrument, and especially the chromatic aberration. A dark glass often improves the view, but not always. Besides, an interposed glass has an unpleasant effect on the field of view. Perhaps the best method of observing Venus is to search for her when she is still high above the horizon, and when therefore the background of the sky is bright enough to take off the planet's glare. The method I have described for the observation of Mercury will prove very useful in the search for Venus when the sun is above the horizon or but just set. Of course, when an object is to be looked for high above the horizon, the two rods which support the cross-rods must not be upright, but square to the line of view to that part of the sky. But the observer must not expect to see much during his observation of Venus. In fact, he can scarcely do more than note her varying phases (see Plate 6) and the somewhat uneven boundary of the terminator. Our leading observers have done so little with this fascinating but disappointing planet, that amateurs must not be surprised at their own failure. I suppose the question whether Venus has a satellite, or at any rate whether the object supposed to have been seen by Cassini and other old observers were a satellite, must be considered as decided in the |
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