## Navigation and Nautical Astronomy, Part 1 |

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20 feet 24 hours added apparent altitude apply astronomical August bearing called celestial centre chronometer showed circle compass course deviation diff difference dist earth east Elements from Nautical equation error EXAMPLES given greater Greenwich date haversines heavenly body height of eye horizontal parallax hour angle index correction interval July June logarithm longitude lower limb March mean sun mean time nearly miles moon moon's names Nautical Almanac noon observed altitude observed meridian altitude pass polar pole reduce refraction rejecting required the latitude required the longitude required the true result right ascension Rule semi Sept ship mean sidereal solar spectator star Star's subtract Sun's declination supposed taken true altitude true bearing true distance variation vers zenith distance

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Page 12 - Fig. 3) loaded on the circular side with lead sufficient to make it swim upright in the water: to this is fastened a line about 150 fathoms long, called the Log-line, which is divided into certain spaces called knots, and is wound on a reel (see Plate VI.

Page 54 - ... consequence of the whirling motion of the earth about its axis, the parts near the equator, which have the greatest velocity, acquire thereby a greater distance from the centre than the parts near the poles.

Page 60 - The hour angle of a heavenly body, is the angle at the pole between the celestial meridian and the circle of declination passing through the place of the body ; thus, zpx is the hour angle of x.

Page 59 - The right ascension of a heavenly body is the arc of the equator, intercepted between the first point of Aries and the circle of declination, passing through the place of the...

Page 61 - The apparent solar day is the interval between two successive transits of the sun's centre over the same meridian.

Page 63 - Mean Solar Day is the interval between two successive transits of the mean sun over the same meridian ; it begins when the mean sun is on the meridian.

Page 13 - ... ascertained at sea by observing the magnetic bearing of- the sun when in the horizon, or at a given altitude abo-ve it. From this observation the true bearing is found by rules given in nautical astronomy. The difference between the true bearing and the observed bearing by compass determines this correction.

Page 258 - W., and at the same time the observed altitude of the sun's lower limb was 21° 40' 45", the index correction was — 2' 18", and the height of the eye above the sea was 14 feet : required the variation.

Page 199 - To the hour angle thus found, add the star's right ascension; and from the sum, increased if necessary by 24 hours, subtract the right ascension of the mean sun ; the remainder is mean time at the place at the instant of observation.

Page 54 - ... path of the sun as seen from the Earth, and is called the Ecliptic. The plane of the Earth's equator, extended till it meets the concave surface of the heavens, forms what is called the Celestial Equator, or the Equinoctial. The ecliptic and the equinoctial form an angle of 23° 28', and this angle is called the Obliquity of the Ecliptic. The axis of the Earth, therefore, instead of being perpendicular to the plane of its orbit, is inclined to it at an angle of (90° — 23° 28') 66° 32'.