On this page, basic astronomical time and position calculations can be made for a given point and date on Earth. The semi-analytical planetary theory VSOP87 (Bretagnon and Francou, 1988, A&A, 202, 309) was adopted for position calculations. The equations used in the calculations are taken from the second edition of Jean Meeus's book "Astronomical Algorithms".*.

When the VSOP87 theory is used, it is predicted that the position of the Sun can be calculated with an accuracy of 1 arc second from -2000 to +6000 years. However, since the difference (ΔT) between universal time (UT) and dynamic time (TD) does not change in a certain order, there is no general model that can sensitively represent the distant past and the distant future. Therefore, ΔT value can be found only through observations. As a result, it should be expected that the sensitivity of the calculations for the distant future and the distant past, where high-precision observations are not available, will be lower.

Earth-Sun distance is given in "Astronomical Units (AU)". The average Earth-Sun distance is defined by the International Astronomical Union (IAU) as 149597870,700 km (IAU 2012, proposal titled B2). In the position calculations, the starting point of the azimuth value is assumed to be north, and the direction of increase is clockwise (towards the east).

Although the calculation results are in most cases consistent with the results from the JPL ephemeris, there may be arc-minute differences in positions. Since very high precision results would be required for purposes such as sending spacecraft to the Moon or a planet, it is much more convenient to use the results from the JPL ephemeris for these kind of purposes, instead of the calculations on this page.

* Meeus, J. “Astronomical Algorithms”. Second edition 1998, Willmann-Bell, Inc.,Richmond, Virginia, USA.