[3] 天球座標系は、天球上の位置を表す座標系です。

[2]

[1] 天球座標系 - Wikipedia (12/22/2016, 11:53:27 AM) <https://ja.wikipedia.org/wiki/%E5%A4%A9%E7%90%83%E5%BA%A7%E6%A8%99%E7%B3%BB>

[4] Celestial coordinate system - Wikipedia ( (4/21/2017, 2:20:35 PM)) <https://en.wikipedia.org/wiki/Celestial_coordinate_system>