Glossary term: 방위각
Description: 지평 좌표계에서 방위각은 하늘의 천체가 수평선을 따라 어느 방향에 있는지를 나타내는 각도입니다. 이 각도는 북쪽을 기준으로 해서 동쪽 방향으로 잽니다. 방위각은 0도에서 360도까지 값이 있으며, 이는 한 바퀴(원)을 모두 포함합니다. 즉, 천구에서 있는 물체에서 지평선까지 가상의 선(호)를 수직으로 내리고, 그 선이 지평선과 만나는 지점이 바로 방위각을 알려줍니다. 하늘의 천체가 바로 북쪽에 있으면 방위각은 0도, 동쪽에 있으면 90도입니다. 옛날 여러 나라에서 쓰이던 교과서에는 남쪽에서 서쪽 방향으로 방위각을 재는 방법을 사용하기도 했습니다. 그래서 그런 교과서의 방위각 값은 현재 우리가 쓰는 값과 180도 차이가 납니다.
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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
