Chinese English

A SMALL CIRCLE on the surface of the EARTH at every point of which, at the instant of OBSERVATION, the observed CELESTIAL BODY (SUN, STAR, or PLANET) has the same ALTITUDE and, therefore, the same ZENITH DISTANCE.

地面上的一种小圆上，在同一时刻在其上任何一点观测某一天体（太阳、恒星或行星）所测得的高度相等，故其天顶距也相等。

The SMALL CIRCLE on the surface of the EARTH on which an OBSERVATION shows the observer to be. The expression is most frequently used to indicate the CIRCLE OF EQUAL ALTITUDE. Also called position circle.

地球表面的小圆，在该小圆上观测者所测得的观测值均相同。该术语经常用于指等高度圈（circle of equal altitude）。亦称为position circle（位置圈）。

A circle having as its centre a POSITION, however determined, and as its radius the maximum PROBABLE ERROR of the POSITION; a circle within which a craft is considered to be located.

(U.S. terminology). A BOAT SHEET or a SMOOTH SHEET on which intersecting systems of curves are drawn, each curve corresponding to the LOCUS of some angle between two STATIONS. POSITIONS are plotted on circle sheets at the intersection of the LOCI of two observed angles, each LOCUS being found by INTERPOLATION between the curves drawn on the sheet. Circle sheets are prepared and employed in HYDROGRAPHIC SURVEYS for plotting FIXES without the use of PROTRACTOR. Also calledstandard circle sheet; formerly calledsextant chart. See also FIXED ANGLE PLOT, and LATTICE.

绘有多组相交曲线的一种测量图板。图板上的每条曲线相当于两站间某一角度的轨迹。在海洋测量中使用这种图板不用分度规就可标出定位点。其方法是先用内插法在曲线之间求出每一测角所对应的轨迹，然后在两轨迹的交点处标出船位。也称作标准圆弧格网图版。最早称作六分仪定位图板。

A RADIO STATION which needs not necessarily be manned, the emissions of which, radiated around the HORIZON, enable its BEARING to be determined by means of the RADIO DIRECTION FINDER of a ship.

一种无需人工操作即可发射无线电波的无线电台站，它沿水下周围方向发射电波，可在船上用无线电测向仪测出其方位。

(adj.). Revolving about the ELEVATED POLE without setting. A CELESTIAL BODY is circumpolar when its POLAR DISTANCE is approximately equal to or less than the LATITUDE of the observer. The actual limit is extended somewhat by the combined effect of REFRACTION, SEMIDIAMETER, PARALLAX, and the HEIGHT of the observer's eye above the HORIZON.

天体不没而绕仰极运转的。天体的极距约等于或小于观测者所处的纬度时，则为拱极天体。拱极的实际范围根据折射、半径、视差以及观测者在地面上眼高的复合效应稍有扩大。