Topic
Based upon the "Astronomical Formulae for calculators" by J. Meeus the ephemeris calculation for the major planets, along with the necessary calendar and time operations have been implemented in a VBA module of an Excel workbook. The time dependent positions of the bodies can be updated periodically with a specific time increment. A graphical output is also featured.
Ephemerides
The elements giving the precise position of a body in the sky are called ephemerides. The "Astronomical Formulae for Calculators" by Jean Meeus explain a compact procedure to calculated the ephemerides in a precision sufficient, e.g. for celestial navigation using heights observed with a sextant.
The version presented in this article is intended for that use and is published as an intermediate result.
The elements for the stellar positions are taken from the Yale Bright Star calatogue.
Concept
The theory by Simon Newcomb used in the "Astronomical Formulae for Calcultors" uses series expansions of the perturbation in planetary orbit elements. The VBA-Code contains quite simple procedures to calculated these perturbations from coefficients input from an Excel worsheet where they are stored. The calculation uses just a geographical position and a date-time in UTC.
Demo
The Video besides shows the graphical output of the calculations in a horizontal star chart. The chart is in equidistant azimuthal projection around the local zenith. As long as "Auto" is set to 1, the calculation is updated every second with the time incremented by the value set.
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