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Earth and Space Sciences · 术语表

什么是 Equatorial coordinates？

又称： declination (celestial) · hour angle · right ascension

Definition 1.8 University Earth and Space Sciences — Year 1 · 第 1 章 — Spherical Astronomy

The declination δ\delta of a star is its angle from the celestial equator, positive to the north, from −90∘-90{}^{\circ} to 90∘90{}^{\circ}. The great circle through the star and the celestial poles is its hour circle. The hour angle HH of the star is the angle at the celestial pole between the local meridian and the star’s hour circle, counted westward, in hours of 15∘15{}^{\circ}. The right ascension α\alpha is the angle along the celestial equator from a fixed point of the sky, the vernal equinox point (Definition 1.12), to the star’s hour circle, counted eastward, also in hours.

The sky at latitude 45 N, seen from the west, north on the left. The north celestial pole P stands at an altitude equal to the latitude above the north point (red: the axis of the celestial poles); the celestial equator (blue) crosses the horizon at the east and west points. A star X of declination 25, three hours twenty minutes after its passage across the meridian (hour angle 50), is at the altitude h = 45.3 (green: its vertical circle, from the zenith Z to the horizon) and the azimuth 261; its hour circle (dash-dotted) runs from the pole through the star to the equator. Computed with .
The sky at latitude 45∘45{}^{\circ} N, seen from the west, north on the left. The north celestial pole PP stands at an altitude equal to the latitude above the north point (red: the axis of the celestial poles); the celestial equator (blue) crosses the horizon at the east and west points. A star XX of declination 25∘25{}^{\circ}, three hours twenty minutes after its passage across the meridian (hour angle 50∘50{}^{\circ}), is at the altitude h=45.3∘h = 45.3{}^{\circ} (green: its vertical circle, from the zenith ZZ to the horizon) and the azimuth 261∘261{}^{\circ}; its hour circle (dash-dotted) runs from the pole through the star to the equator. Computed with Proposition 1.9.
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