LESSON 15: Celestial Coordinate Systems

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´╗┐LESSON 15: Celestial Coordinate Systems Learning Objectives Know a definitive objective of divine route. Know the meanings of terms and parts connected with the earthly, heavenly , and skyline facilitate frameworks. Know the relationship between the earthbound, heavenly , and skyline organize frameworks. Apply rectify techniques to depict the area of a divine body in reference to the heavenly and skyline organize frameworks.

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The Goal of Celestial Navigation The arrangement of circular triangles of sides in view of the watched places of heavenly bodies, to decide the position of a vessel. 100 years back, this included some convoluted round trigonometry. Today, it requires the utilization of tables or a navigational mini-computer (HP makes one).

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1. Earthbound Coordinate System A snappy audit :

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Basic Assumptions First, expect the earth does not move, but rather the divine bodies turn about it in an anticipated way. The divine circle: heavenly bodies are thought to be on the internal surface of a boundless, empty circle of interminable span, which has the earth at its inside.

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2. Divine Coordinate System The heavenly organize framework is best comprehended as a projection of the earthly arrange framework, outward into space onto the divine circle .

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Celestial Coordinate System Celestial Equator (Equinoctial) Celestial Meridians Hour Circles Hour Circle of Aries Declination heavenly likeness scope Hour Angles divine likeness longitude

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Hour Angles Three unique references are utilized: Sidereal Hour Angle (SHA) Hour Circle of a divine body, as referenced from the hour hover of Aries (measured westerly) Greenwich Hour Angle (GHA) Hour hover of a divine body, as measured in respect to Greenwich Celestial Meridian Local Hour Angle (LHA) Hour hover of a heavenly body, as measured in respect to the nearby divine meridian

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Hour Angles GHA = GHA(Aries) + SHA

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3. Skyline Coordinate System In the earthbound and divine arrange frameworks, the essential references are the posts and the equator. The skyline facilitate framework, be that as it may, depends on the spectator's position. This framework is vital on the grounds that stars are located as for the eyewitness' position.

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Horizon Coordinate System Zenith and Nadir closely resembling north and south posts Vertical Circle similar to meridian (earthly framework) or hour circle (heavenly framework) Prime Vertical (east and west) Principal Vertical (north and south)

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Horizon Coordinate System

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Horizon Coordinate System Celestial Horizon practically equivalent to the equator True Azimuth (Z n ) undifferentiated from longitude Altitude comparable to scope Sextant Altitude (h s ) Measured heights of divine bodies Visible or Sea Horizon Used as a kind of perspective for heavenly body elevation estimations Observed Altitude (H o ) Conversion of Sextant Altitude, since ocean skyline is not at divine skyline.

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The Celestial Triangle These three facilitate frameworks (TERRESTRIAL, CELESTIAL , AND HORIZON ) are then joined to shape the divine triangle, which is utilized to decide our position. One leg from every triangle frames the new triangle on the heavenly circle.

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The Celestial Triangle

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The Celestial Triangle Azimuth Angle (Z) Meridian point (t)

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Coordinate System Comparison