天文常数中的相对论问题

Relativistic Problems on Astronomical Constants

现代天文观测技术的日新月异、广义相对论的IPN近似方法在天体力学和天体测量中的广泛应用，使得有必要在IPN框架中严格而细致地重新审查天文常数系统。在相对论框架里，太阳系天体的质量应当定义为BD质量，它们的相对变化不超过10(-19)，可视为守恒量;引力势满足的方程不再是Poisson方程而与坐标规范的选择有关，引力势也不再能用传统的球谐函数展开。应当选定一种规范，并且以BD多极矩作为天文常数。黄赤交角已有很高的精度，因而有必要给出相对论黄道的协议定义。大地水准面的相对论定义更是有待今后研究的一个重要问题。相对论框架里与时间和长度单位有关的天文常数已有清晰的定义，对其应有准确的理解以防止错误应用。

The fact that the modern astronomical observational technique has made rapid progress and the IPN approximation of general relativity has been extensively applied in celestial mechanics and astrometry, makes it is necessary to investigate and examine the system of astronomicalconstants carefully and rigorously in the relativistic framework. The mass of a celestial body in the solar system should be defined as its BD mass that changes relatively in an amount less than 10-19 and could be considered as a constant. The equations satisfied by the gravitationalpotentials are not Poisson equations anymore but depend on the choice of the coordinate gauge.Therefore the gravitational potentials cannot be expanded in the traditional harmonics. It is neccessary to choose the coordinate gauge and take BD multipole moments as astronomical constants. The obliquity of the ecliptic has been determined in high precision and it would be neccessary to give a conventional definition of the IPN ecliptic. A relativistic definition of the geoid is important and left to be discussed. The astronomical constants that relate the units of time and length have been clearly defined but need to be clarified to avoid their misuse.