ATP-3-09-02 Field Artillery Survey Download
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Survey Methods 16 February 2016 ATP 3-09.02 7-15 Figure 7-11. World star chart 7-38. The two projections by which star charts are plotted are cylindrical (similar to the Mercator projection for world maps) and plane (similar to polar projection for world areas). The cylindrical projection presents great distortion about the poles of the celestial sphere but offers a fairly accurate picture in declination to ±65°. It should be remembered that in such a projection the vertical lines plotted to be parallel actually converge at the poles and are perpendicular to the equator. The plane projection presents a truer picture of the sky, especially if it is used with a mark that blocks out all the sky except that within the horizon for a given area. 7-39. The brightness of stars is measured in magnitude. Thus, the brightest stars are of the first magnitude, the next in brightness are of the second magnitude, and so forth. Stars in constellations, some of which have individual names (for example, Polaris), are usually named in the constellation in order of their brightness through the use of the Greek alphabet. Thus, in the constellation Orion, from the brightest to the least bright, the stars are named (Betelgeuse [also Betelgeux]), (Rigel), (Bellatrix), and so forth. The magnitude of each star is shown on star charts.