5/8/2021 0 Comments Sextant Calculaision Software
Thanks to precession, the celestial prime meridian passes through the constellation Pisces.Up-time celestial navigation methods may thus save not just their reputations, but their lives.It is complicated because the apparent position is also dependent on the rotation of the earth about its axis, and the revolution of the earth about the Sun, and thus on the passage of time.For the Moon and the planets, it is also affected by their own motion about the Earth and Sun, respectively.).
Admiral Simpson, and some of the other navy veterans, will certainly have taken a navigation course at some point during their naval career. And the Ed Board has decreed that there are at least two copies of pre-1995 editions of Bowditchs American Practical Navigator. Chances are reasonably good that they are members of the U.S. Power Squadron. The nearest chapter is the Kanawha River Power Squadron in Charleston, West Virginia, and it offers courses in Seamanship, Piloting, Advanced Piloting and Celestial Navigation 1 and 2. In fact, Omar Khayyam referred to that inverted bowl they call the sky. The stars (including the Sun) appear to move across the celestial sphere as a result of the rotation of the Earth, and the revolution of the Earth around the Sun. The apparent motion of the Moon and planets is a composite of their true motion, and the apparent motion generated by the Earth. If we want to use the heavenly bodies as guides to navigation, then we need to be able to describe their positions in the sky. First, we have to decide the origin (math talk for where we imagine we are standing when we measure the positions). The choices are heliocentric (measured from the center of the Sun), geocentric (from the center of the earth), or topocentric (from a point on the earths surface) form. The difference between geocentric and topocentric measurements is likely to be noticeable only for the Moon. There are three principal coordinate systems: equatorial, ecliptic and alt-az. At a planetarium, you could project a grid onto the screen, representing the lines of celestial latitude and longitude. In the equatorial system, the plane of reference is the celestial equator: the projection, into the sky, of the terrestrial equator. Likewise, the North Celestial Pole (NCP) is directly above the Earths North Pole, and the South Celestial Pole below the Earths South Pole. Celestial latitude, measured from the equator, is called declination, and is measured in degrees, arc-minutes (), and arc-seconds (). In 1950, it was defined as passing through the first point in the constellation Aries. RA is stated either like declination, or, because of the relationship of longitude to local time, in hours, minutes (m) and seconds (s) (one minute RA is 15; one second, 15). Geocentric equatorial coordinates work well for the Sun and the stars, at least in the short term (years as opposed to centuries), but for the planets, it helps to carry out computations in ecliptic coordinates. The earths orbital plane is called the ecliptic, and a line drawn through the center of the Earth, and perpendicular to the ecliptic, defines the North and South Ecliptic Poles. Depending on what you are trying to compute, you can use geocentric or heliocentric coordinates. Celestial North has to be defined on the basis of the orientation of the Earths axis, relative to its orbit, as of a particular time (epoch).
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