Half-hours with the Telescope: A Popular Guide to the Use of the Telescope as a Means of Amusement and Instruction |
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Common terms and phrases
61 Cygni Albireo Algol Almanac alt-azimuth Andromeda aperture appears Arcturus astronomical axis blue brilliant Cassiopeia Castor centre cluster colours companion components constellation convex lens Cor Caroli Cygni Cygnus dark Dawes diameter directed disc distance distinct vision double star easy double ecliptic emergent pencils equator Equuleus exhibit eye-glass eye-piece eye-tube favourable field of view finder focal length focus formed glass HALF-HOUR heavens Herschel horizon hour Howlett Huggins instrument interesting inverted Jupiter Jupiter's light look low power Lyræ magnitude maps Mars Mercury meridian method Milky moderate power moon motion naked eye nearly nebula noticed object object-glass observer Ophiuchi Orion pass planet powerful telescope quadrature red star right ascension rings satellites Saturn Scorpionis screen seen Serpentis shadow shown in Plate Sirius smaller solar spherical aberration spot sun's supposed tele telescopist trapezium tube turn variable Vega visible wide double yellow zenith
Popular passages
Page 97 - Hercynian mountains, within a circumvallation called Lichtenburg. The brightest portion of the whole lunar disc is Aristarchus, the peaks of which shine often like stars, when the mountain is within the unillumined portion of the moon. The darkest regions are Grimaldi and Endymion, and the great plain called Plato by modern astronomers — but, by Hevelius, the Greater Black Lake. But although there are varieties, there has never yet been detected any variation of colour.
Page 96 - ... tone, but in the photographic quality of the light they reflect towards the earth. Some of the seas exhibit a greenish tint, as the Sea of Serenity and the Sea of Humours. Where there is a central mountain within a circular depression, the surrounding plain is generally of a bluish steel-grey colour. There is a region called the Marsh of Sleep, which exhibits a pale red tint, a colour seen also near the Hyrcinian mountains, within a circumvallation called Lichtenburg.
Page 95 - Maraldi, precisely because they are now recognized as snow-covered regions, increasing in the martial winter and diminishing in the martial summer. It is in this relation that we have spoken of the moon as the most disappointing object of astronomical observation. For two centuries and a half, her face has been scanned with the closest possible scrutiny ; her features have been portrayed in elaborate maps ; many an astronomer has given a large portion of his life to the work of examining craters,...
Page 41 - ... we could plainly see that all about the trapezium is a mass of stars ; the rest of the nebula also abounding with...
Page 13 - To remedy this defect, achromatic lenses were formed by the union of a convex lens of crown glass with a concave lens of flint glass.
Page 17 - K e' respectively work, are so fastened by elastic cords that an upward pressure on the handle h, or a downward pressure on the handle h', at once releases the endless screw or the crown-wheel respectively, so that the telescope can be swept at once through any desired angle in altitude or azimuth. This method of mounting has other advantages : the handles are conveniently situated and constant in position ; also, as they do not work directly on the telescope, they can be turned without setting the...
Page 76 - After the thirty-six pages assigned to the months follow four (pp. 42-46) in which much important astronomical information is contained ; but the points which most concern our observer are (i.) a small table showing the appearance of Saturn's rings, and (ii.) a table giving the hours at which Jupiter's satellites are occulted or eclipsed, re-appear, &c. We will now take the planets in the order of their distance from the sun : we shall see that the information given by the almanac is very important...
Page 96 - ... regions which one would be apt to speak of as snow-covered, if one could conceive the possibility that snow should have fallen where (now, at least) there is neither air nor water. Then there are the so-called seas, large gray or neutral-tinted regions, differing from the former not merely in color and in tone, but in the photographic quality of the light they reflect towards the earth. Some of the seas exhibit a greenish tint, as the Sea of Serenity and the Sea of Humors. Where there is a central...
Page 94 - ... unusually symmetrical circular formation makes its appearance; the exterior surface of the wall bristling with terraces rising gradually from the plain, the interior one much more steep, and instead of a flat floor, the inner space is concave or cup-shaped, with a solitary peak rising in the center. "Solitary peaks rise from the level plains and cast their long, narrow shadows athwart the smooth surface. Vast plains of a dusky tint become visible, not perfectly level, but covered with ripples,...
Page 16 - The casings at e and e', in which the rods he and h' e respectively work, are so fastened by elastic cords that an upward pressure on the handle h or a downward pressure on the handle h' at once releases the endless screw or the crown wheel respectively, so that the telescope is free to be swept at once through any desired angle either in altitude or azimuth. This method of mounting has other advantages — the handles are conveniently situated and constant in position ; also as they do not work...