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歳差運動

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A sidereal day is one Earth rotation relative to the stars; a solar day is one Earth rotation relative to the Sun. The Earth rotates about 366 times per 'normal' 365-day year relative to the stars, so Earth's sidereal day is about four minutes shorter than Earth's solar day. (Angle exaggerated for visibility.)

恒星時とは？太陽時との違いと天文学における重要性を解説

恒星時太陽時恒星日太陽日
2026年8月11日続きを読む →
The positive pole of a planet is defined by the right-hand rule: if the fingers of the right hand are curled in the direction of the rotation then the thumb points to the positive pole. The axial tilt is defined as the angle between the direction of the positive pole and the normal to the orbital plane. The angles for Earth, Uranus, and Venus are approximately 23°, 97°, and 177° respectively.

自転軸の傾き（黄道傾斜角）が惑星の気候と季節に与える影響

自転軸の傾き黄道傾斜角季節のメカニズム地球の公転
2026年8月11日続きを読む →
Precessional movement of Earth. Earth rotates (white arrows) about once a day around its rotational axis (red); this axis itself rotates slowly (white circle), completing a rotation in approximately 26,000 years[1]

地軸の歳差運動地球の回転軸が描く26,000年の巨大なサイクル

歳差運動地軸春分点天文学
2026年8月11日続きを読む →
Illumination of Earth by the Sun on the day of an equinox

春分点（3月の分点）の天文学的メカニズムと世界文化への影響

春分天文学春分点昼夜等分
2026年8月11日続きを読む →
Precession of a gyroscope[clarification needed]

歳差運動のメカニズム物理学から天文学まで徹底解説

歳差運動ジャイロスコープ角運動量春分点歳差
2026年8月11日続きを読む →
As seen from the orbiting Earth, the Sun appears to move with respect to the fixed stars, and the ecliptic is the yearly path the Sun follows on the celestial sphere. This process repeats itself in a cycle lasting a little over 365 days.

黄道面とは何か？太陽の通り道と天球座標系の基礎知識

黄道黄道面天球地球の公転
2026年8月11日続きを読む →
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回帰年とは？太陽の周期とカレンダーの仕組みを解説

回帰年太陽年グレゴリオ暦春分点
2026年8月11日続きを読む →
Orbital inclination and rotation. When the Moon is 5.14° north of the ecliptic, its north pole is tilted 6.68° away from the Earth. The orientation of the plane containing the vectors normal to the orbits and the Moon's rotational axis rotates 360° with a period of about 18.6 years, whereas the Earth's axis precesses with a period of around 26,000 years, so the line-up of this illustration (a major lunar standstill) occurs only once every 18.6 years.

カッシーニの法則月の自転軸と公転軌道の不思議な関係

カッシーニの法則月の自転公転軌道カッシーニ状態
2026年8月11日続きを読む →
The celestial equator is currently inclined by about 23.44° to the ecliptic plane. The image shows the relations between Earth's axial tilt (or obliquity), rotation axis, and orbital plane.

天球赤道とは？地球の傾きと星空の座標系を解説

天球赤道天球黄道地軸
2026年8月11日続きを読む →
Orbital dynamics of the Moon, with exaggerated paths and sizes, particularly illustrating that the Moon's orbit is on average slightly more outbound than inbound around the Sun, perturbed by Earth.[6]

月軌道のメカニズム地球とのダイナミックな相互作用

月軌道地球重心
2026年8月10日続きを読む →