воскресенье, 25 марта 2012 г.

The ecliptic. Ecliptic coordinate system

Measurements of the zenith distance or altitude of the sun at noon (ie, at the time of upper culmination) at the same latitude was found that the declination of the sun throughout the year varies between 23 e 27 'up-23e27' twice a year passing through zero. From observations of the night sky kind of change that, and right ascension of the sun throughout the year and gradually changes from 0 € to 360e, or from 0h to 24h. Indeed, at midnight, at the top are the culmination of the stars, right ascensions of which differ from the right ascension of the sun on the 180e or 12h. The observations also show that every day at midnight stars culminate with more and more direct ascent, consequently, the right ascension of the sun each day increases. Considering the continuous change of both the origin of the sun, it is easy to install, it moves among the stars from west to east along the great circle of the celestial sphere, called the ecliptic. The plane of the ecliptic E'' ^ E d (11) is inclined to the plane of the celestial equator at an angle e = 23rd 27 '. The diameter of PP ', perpendicular to the plane of the ecliptic, the ecliptic is called the axis and intersects with the surface of the celestial sphere in the ecliptic north pole P (which lies in the northern hemisphere) and south pole of the ecliptic P' (in the Southern Hemisphere). The ecliptic intersects the celestial equator at two points: at the vernal equinox ^ and at the autumnal equinox d. At the point of the vernal equinox ^ Sun crosses the celestial equator, moving from the southern hemisphere to the northern celestial sphere. At point d the autumnal equinox the Sun moves from the northern to the southern hemisphere. Point of the ecliptic, are separated from the equinoctial to the 90s, called the point of the summer solstice (northern hemisphere) and the point of the winter solstice (Southern Hemisphere). Large semi-circle of the celestial sphere PMP ', passing through the ecliptic poles and through the M star, is called the circle of latitude star. The ecliptic and the vernal equinox are the basis of the ecliptic celestial coordinate system. One coordinate in this system is the ecliptic latitude b luminaries M, which is called the arc of a circle of latitude mM (see 11) of the ecliptic to the celestial body, or the central angle between the plane of the ecliptic TOM and the direction of light M. Ecliptic latitude are measured in the range from 0 € to + 90 ° to the ecliptic north pole (P) and from 0 € to - 90 ° to its south pole (S '). Luminaries that are on the same small circle whose plane is parallel to the ecliptic plane, have the same ecliptic latitude. Ecliptic latitude determines the position of lights in the circle of latitude. The position of the same circle of latitude on the celestial sphere is determined by the coordinate of the other - the ecliptic longitude l. Ecliptic longitude l is the arc lights in M ​​^ m the ecliptic from the vernal equinox ^ to the circle of latitude that passes through the star, or a central angle ^ from (in the ecliptic plane) between the direction of the vernal equinox and the plane of the circle of latitude that passes through the light. Ecliptic longitude are measured in the direction of the apparent annual motion of the sun on the ecliptic, ie, from west to east in the range from 0 € to 360e. Luminaries that are on the same circle of latitude, have the same ecliptic longitude. Ecliptic coordinate system is used mainly in theoretical astronomy in determining the orbits of celestial bodies.

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