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Declination (Dec) is the celestial equivalent of latitude, representing the angle north or south of the celestial equator. It is used in conjunction with Right Ascension to provide a complete coordinate for locating celestial objects and is expressed in degrees, arcminutes, and arcseconds.

The Hour Angle of a celestial object is the angle between the observer's meridian and the meridian containing the object. It is equivalent to the time since an object has transited, with negative values for objects yet to transit. Hour Angle is often used in conjunction with Declination for locating objects in the sky.

The Celestial Meridian is an imaginary line in the sky that runs from the north celestial pole to the south celestial pole, passing through the zenith of the observer's location. It divides the sky into the eastern and western hemispheres and is used for measuring Hour Angle.

Right Ascension (RA) is the celestial equivalent of terrestrial longitude, indicating the angle measured eastward along the celestial equator from the vernal equinox. It is used to pinpoint positions of objects in the sky and is usually expressed in hours, minutes, and seconds.

Galactic Coordinates measure positions in terms of Galactic Longitude and Galactic Latitude with respect to the plane of the Milky Way Galaxy. This system is useful for mapping and studying the structure of the galaxy itself.

The Horizontal Coordinate System (Altitude-Azimuth System) is based on the observer's local horizon, using Altitude to measure the angle above the horizon, and Azimuth for the angle along the horizon from the north point. It is crucial for practical observational astronomy, particularly in navigation.

The Ecliptic Coordinate System is based on the plane of Earth's orbit around the Sun and uses Ecliptic Longitude and Ecliptic Latitude to specify the position of celestial bodies relative to this plane. It is often used for describing the positions of solar system objects.

The Celestial Equator is the great circle on the celestial sphere directly above Earth's equator. It provides a reference for measuring Right Ascension and Declination, and is particularly relevant for indicating the equinoxes and tracking Earth's axial precession.

The Vernal Equinox is the point on the celestial sphere where the Sun crosses the celestial equator moving northward. It serves as the zero point for Right Ascension and is one of the two intersections of the ecliptic and celestial equator. The Vernal Equinox marks the beginning of spring in the northern hemisphere.