Fundamental properties of the planet Venus, such as its internal mass distribution and variations in length of day, have remained unknown. We used Earth-based observations of radar speckles tied to the rotation of Venus obtained in 2006–2020 to measure its spin axis orientation, spin precession rate, moment of inertia and length-of-day variations. Venus is tilted by 2.6392 ± 0.0008 deg (1σ) with respect to its orbital plane. The spin axis precesses at a rate of 44.58 ± 3.3 arcsec per year (1σ), which gives a normalized moment of inertia of 0.337 ± 0.024 and yields a rough estimate of the size of the core. The average sidereal day on Venus in the 2006–2020 interval is 243.0226 ± 0.0013 Earth days (1σ). The spin period of the solid planet exhibits variations of 61 ppm (~20 min) with a possible diurnal or semidiurnal forcing. The length-of-day variations imply that changes in atmospheric angular momentum of at least ~4% are transferred to the solid planet.

金星的基本特性，例如其内部质量分布和白天长度的变化，仍然未知。我们使用在 2006 年至 2020 年获得的与金星自转相关的基于地球的雷达散斑观测来测量其自旋轴方向、自旋进动率、惯性矩和日长变化。金星相对于其轨道平面倾斜 2.6392 ± 0.0008 度 (1 σ )。自旋轴以每年 44.58 ± 3.3 弧秒 (1 σ ) 的速率进动，这给出了 0.337 ± 0.024 的归一化惯性矩，并得出核心大小的粗略估计。2006-2020 年金星平均恒星日为 243.0226 ± 0.0013 个地球日（1 σ）。固体行星的自转周期表现出 61 ppm（约 20 分钟）的变化，可能存在昼夜强迫或半昼强迫。日长变化意味着至少约 4% 的大气角动量变化会转移到固体行星上。