ATP-3-09-02 Field Artillery Survey Download
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Survey Methods 16 February 2016 ATP 3-09.02 7-11 because of its slow movement. However, Polaris cannot be seen in many parts of the Northern Hemisphere because of local weather conditions, and it cannot be used in areas close to the equator and in the Southern Hemisphere. Therefore, it is inadvisable to depend solely on this star for night observations. Methods of ID and approximate locations of the stars on the celestial sphere in relation to the observer's position are presented in Section IV. All artillery surveyors must be familiar with the more common stars and their relative positions in the sky. STAR SELECTION AND IDENTIFICATION 7-32. There are important advantages to using stars, rather than the sun as sources of an astronomic azimuth. Since they appear as pinpoints of light in instrument telescopes, stars are easier to track than the sun. At least one of the usable 73 can usually be found in a satisfactory position for observation regardless of the time of night or the observer's latitude. The North Star (Polaris) should always be used when the geographical location and tactical situation permit. When the telescope is directed at Polaris, the observer will see two other stars nearby that are not visible to the naked eye. However, Polaris will be the only star visible when the cross hairs are lighted. STAR FINDER AND IDENTIFIER 7-33. The star finder and identifier (figure 7-7 on page 7-12) is a device used to determine the approximate (±2°) azimuth and altitude of a given star. This device is issued as a component of the survey set, artillery fire control, fourth-order. The star finder and identifier consist of a base, 10 templates, and a carrying case. The base is reversible with stars of the Northern Hemisphere on one side and stars of the Southern Hemisphere on the other. There is one template for each 10° of latitude from 5° to 85° (5°, 15°, 25°, 35°, and so forth). (The tenth template, designed for plotting the sun and planets, is not used in artillery survey). Each template is reversible with one side for north latitude and the other side for south latitude. The template constructed for the latitude nearest the latitude of the observer should be used. The base of the star finder in Figure 7-7 shows the stars visible in the Northern Hemisphere. The center of the device represents the celestial North Pole. The edge of the base is a circle graduated in degrees and half degrees, representing the local hour angle of the vernal equinox or the local sidereal time. On each template is a series of concentric ellipses. Around the outer edge of these ellipses are two sets of numbers from 0° to 360°. The inner set of numbers starts at the top of the template for north latitude and increases in a clockwise direction. The outer set of numbers starts at the bottom of the template for south latitude and increases in a clockwise direction around the ellipses. In the Northern Hemisphere, the inner figures are used; in the Southern Hemisphere, the outer figures are used. The inner set of figures represents the azimuth from the celestial North Pole to the line that the figures identify. The outer set of figures represents the same thing except that the azimuth is from the celestial South Pole to the line. The series of concentric ellipses represents altitudes above the horizon. The template has the horizon on its circumference, the zenith as its center, and a measure of azimuth around the edge. The 0° to 180° line represents the observer's meridian. Before the star finder can be oriented, the value of the local sidereal time must be determined. The pointer of the template is then placed over the appropriate value on the base of the star finder.