The upper conjunction is the celestial event when an inner planet (with respect to an observer on earth , i.e. Mercury or Venus ) is exactly behind the sun . In this case it shows us its fully illuminated side (similar to the full moon ) and passes unnoticed mostly north or south of the sun.
If an upper conjunction takes place near the orbital nodes of the orbit of Mercury or Venus, these planets can be covered by the solar disk, but this cannot be observed due to the enormous difference in brightness.
- Andreas Guthmann: Introduction to celestial mechanics and ephemeris calculus . 2nd Edition. Spektrum Akademischer Verlag, Heidelberg, Berlin 2000, ISBN 3-8274-0574-2 , pp. 191 .