## An Introduction to the Elements of Practical Astronomy |

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Almanac altitude amount angle apparent applied Ascension assumed axis body bright limb called celestial centre circle clock consider continually correction corresponding course declination dependent determination deviation difference direction earth east Eclipse Reapp effect elapsed enable equal equator equinox error Examples fact former give given Greenwich mean heavens horizon horizontal parallax hour indicated instant instrument interval known latitude light longitude lower marked mean mean solar measured meridian middle moon motion moves November object obtain orbit origin parallel particular passes perpendicular place of observation plane point of Aries polar distance pole position practical present principle reference refraction remains result Right rotation round satellite seconds seen semidiameter side sidereal star successive sun's supposing surface Table telescope tion transit triangle true distance turned values vertical whence wire zenith distance

### Popular passages

Page 8 - When a ray of light passes from one medium to another, it is refracted so that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the velocities in the two media.

Page 33 - Find the latitude of the place and the declination of the star. What instrument would you use, in making these determinations and why ? 3. Find the declination of a star whose meridian zenith distance in a place whose latitude is 50° 22' iŤ 70° 10

Page 34 - The names of the signs of the zodiac are: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricornus, Aquarius, and Pisces.

Page 57 - PM was 70° 58', the height of the eye being 21 feet above the surface of the sea. Required the true latitude of the ship ? Answer, 39° 28' N. 2. Being at sea in latitude 50° 40

Page 32 - ... the altitude of the pole is equal to the latitude of the place (art.

Page 102 - December 37 for the sake of convenience. This inclination is ever varying, as well from the effect of its mean diminution, as of the nutation of the earth's axis: it is an important element in deducing...

Page 39 - Both days are divided into 24 hours ; each hour into 60 minutes ; and each minute into 60 seconds ; the seconds are sub-divided decimally.

Page 102 - The longitude of any place is the arc of the equator, intercepted between the meridian of that place and the first meridian; the longitude, therefore, is the measure of the angle between the two meridians.

Page 3 - Since an oblate spheroid is generated by the revolution of an ellipse about its minor axis, the equator and all the sections of the spheroid parallel to the equator are circles, and all sections made by planes passing through the axis of revolution are equal ellipses. Let a and b represent the lengths of the semi-major and semi-minor axes of this meridian ellipse, which...

Page 67 - The disciples of Plato contributed not a little to the advancement of optics, by the important discovery they made, that light emits itself in straight lines, and that the angle of incidence is always equal to the angle of reflection. Plato terms colours " the effect of light transmitted from bodies, the small particles of which were adapted to the organ of sight.