Glossary term: 지평선
Description: 지평선은 하늘과 지표면을 구분하는 경계선입니다. 지구상 어느 위치에 있든 우리는 전체 지구의 일부분만 볼 수 있습니다. 이처럼 볼 수 있는 부분과 볼 수 없는 부분을 구분하는 경계를 흔히 지평선이라고 합니다. 천문학에서는 이같은 정의를 다음과 같이 세분화합니다: 먼저 지구상에서의 우리 자신의 위치를 기준으로 아래쪽 방향(추를 매단 수직선을 사용하여 확인할 수 있음)에 수직인 지평면을 정의합니다. 이 평면과 천구 간의 교차선이 천문학적 국부지평선이 됩니다. 지평 좌표계는 이러한 지평면을 사용하여 천구상의 위치를 정의합니다. 천체를 향한 우리의 시선과 지평면 사이의 각도를 그 천체의 고도라고 하고, 지평면에 투영된 시선과 진북 방향 사이의 각도를 그 천체의 방위각이라고 합니다.
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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 저작자표시 4.0 국제 (CC BY 4.0) icons
