Glossary term: Horizonte
Description: El horizonte es la línea divisoria que separa el cielo de la superficie terrestre. Desde cualquier punto de la Tierra, solo vemos una parte limitada del globo terráqueo. La línea que separa lo que podemos ver de lo que no vemos se denomina comúnmente «horizonte». En astronomía, esa definición se precisa de la siguiente manera: nuestra propia posición en la Tierra define un plano horizontal, que es perpendicular a la dirección hacia abajo (que podemos visualizar utilizando una plomada). La intersección de ese plano con la esfera celeste define nuestro horizonte local astronómico. El sistema de coordenadas horizontales utiliza el plano horizontal para definir posiciones en el cielo. El ángulo entre nuestra línea de visión hacia un objeto y el plano horizontal se denomina altitud del objeto; el ángulo entre la proyección de la línea de visión sobre ese plano y el norte verdadero se denomina azimut del objeto.
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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher The translation of this term and its definition is still awaiting approval
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Related Diagrams
Horizontal Coordinate System
Caption: This image shows the horizontal coordinate system of an observer on Earth. On the right we see the coordinate system in the local context of the observer. The observer appears here as a point surrounded by the celestial sphere. The ground appears as a plane, while the Earth is round, we can approximate the ground in the area around the observer as a plane. The line where this plane intersects with the celestial sphere is the horizon. The point directly above the observer is the zenith, the point directly below the observer is the nadir which is hidden by the ground.
Two coordinates define this coordinate system, altitude and azimuth, hence the reason this sometimes called an alt-az coordinate system. The altitude is zero at the horizon, maximum (90°) at the zenith and minimum (-90°) at the nadir. Azimuth is the angle around the horizon. Most commonly this is defined to be zero in the direction of north. Any point on the celestial sphere can be defined by these two coordinates. However what objects appear on these position will depend on the time and the location of the observer.
On the left-hand part of the diagram, we can see that when we put the observer and their local horizontal coordinate system in a global context, that the parts of the sky the observer can see depend on their position on the Earth and on the rotation of the Earth. The zenith points perpendicular to the Earth's surface so the position on the sky the zenith and nadir correspond to is dependent on the observer's latitude. The horizon also depends on the observer's position on the Earth.
Credit: Maria Cristina Fortuna/IAU OAE
License: CC-BY-4.0 Creative Commons Reconocimiento 4.0 Internacional (CC BY 4.0) icons
