预报大行星,月球掩点源事件的一种方法

以ＪＰＬ提供的太阳系天体数值历表ＤＥ２００／ＬＥ２００和美国海军天文台提供的岁差、章动改正程序为出发点，本文介绍预报大行星、月球掩源的一种方法，本方法分三个步骤：首先给出被掩源所满足的必要条件，并据此进行被掩源的初选；其次预报掩事件的全局情况，即掩发生的始终时刻和比较精确的地球椭球表面上可观测区域边界，在可观测区域边界中，本文发现了文献中未见出现过的出没南北界最后；预报地方见掩情况。

A METHOD OF PREDICTING OCCULTATIONS OF POINT SOURCES BY PLANETS AND THE MOON

Starting with the numerical ephemeris of the celestial bodies in the solar system,DE200/LE200, constructed by JPL,and the routines for the correction of precession and nutation, provided by the USNO,this paper proposes a method of predicting occultations of point sources(star or radio sourse)by planets and the Moon.This method is divided into three steps.First,a necessary condition for the occulted sources by a specified body and in a given period is presented.We have calculated the data which,with arbitrarily given source catalog(s),can be used for getting the coordinate ranges of the sources that might be occulted by planets or the Moon between Jan.1,1995 and Jan.1,2050,in both mean equatorial and mean eliptic system of J2000.0.These ranges can lessen the works in a selection of occultation candidates among a catalog of sources.The second step is to predict the globular circumstances:the begining and the ending instants,the precise boundary of a region on the surface of the spheroid of the Earth in which the occultation is observable.We have discovered that there exists a set of north-south rise-set boundary points where the shadowed source rises and sets at the same time.As far as we know,it has never been described before.The final step is to predict the local information of an occultation at an observational site.A FORTRAN routine has been written to carry out this method and our numerical results have been compared with that in references1-3]to certify our method.