真近点角（，也可以写成）在天文学是轨道平面上，卫星与近地点之间的椭球焦点角距，如图中的角z-s-p。

椭圆轨道的真近点角可以从轨道状态矢量]]计算如下：

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对圆轨道可以简化成：

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如果圆轨道的轨道角也是0，还可以再简化成：

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In celestial mechanics, true anomaly is an angular parameter that defines the position of a body moving along a Keplerian orbit. It is the angle between the direction of periapsis and the current position of the body, as seen from the main focus of the ellipse (the point around which the object orbits).