## Navigation and nautical astronomy |

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### Common terms and phrases

apparent altitude azimuth calculation the latitude celestial concave celestial equator celestial meridian circle of altitude circle of declination CLEARING THE DISTANCE colatitude compass bearing computed Construct a figure correction cosec difference dist diurnal parallax earth east ecliptic EXAMPLES FOR PRACTICE find by calculation find the angle find the latitude find the true formula Given the altitude Given the meridian Greenwich date Greenwich mean heavenly body horizontal parallax Let nwse represent logarithms longitude by chronometer mean solar meridian altitude moon Nautical Almanac nearly nzs the celestial observed point of Aries pole star PROBLEM ra mean sun reduced latitude reduced zenith distance represent the horizon right ascension ship mean sidereal clock spherical triangle pxy star's hour-angle star's ra subtractive sun's true triangle zpx true bearing true distance true latitude true zenith distance tude variation vers versines west of meridian

### Popular passages

Page 7 - The longitude of a heavenly body is the arc of the ecliptic intercepted between the first point of Aries and the circle of latitude passing through the place of the heavenly body in the celestial concave, measuring from the first point of Aries, eastward, from 0° to 360°.

Page 6 - ... equator intercepted between the first point of Aries and the circle of declination passing through the place of the body in the celestial concave.

Page 14 - 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 5 - ... 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 13 - Strictly, the sidereal day is the interval between two successive transits of the first point of Aries J across any selected meridian.

Page 155 - ... always corresponded to the north point of the horizon. Three corrections are sometimes necessary to be applied to the course steered by compass, to reduce it to the true course ; and the converse. These are called 1 . The Leeway. 2. The Variation of the Compass. 3. The Deviation of the Compass. i. LEEWAY.

Page 6 - The points of the horizon through which the celestial meridian passes are called the north and south points. A circle of altitude at right angles to the meridian is called the prime vertical : thus wz E is the prime vertical.

Page 7 - 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 4 - ... 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'.

Page 165 - When the difference of latitude and departure are computed in this manner up to 45°, the diff. lat. and dep. for courses above 45° may be found by interchanging the titles to the columns. Thus, let it be required to find the diff. lat. and dep. for course 65°, and distance 26 miles : diff. lat. for 65°=26 cos.