To use this form, you must supply the latitude and longitude of your observing site, the date, and
the time (UT). You must also know the calibration constants (Vo) for your instrument. The
Earth/sun distance is also
required, in units of astronomical units (AU). For an approximate
calculation, use a value of 1. Earth is farther from the sun in the
summer than in the winter. In mid-June it is about 1.016 AU from the sun.
In mid-January, it is about 0.984 AU from the sun.