The smaller dome above the altar is decorated with astrological depictions of star constellations. The arrangement of the constellations is accurate enough to estimate the particular date they represent, although there has been disagreement on the intended date represented there. In 1911, Aby Warburg first made an attempt with the help of a Hamburg astronomer and concluded that the date was the July 9, 1422, the date of the consecration of the altar. Gertrud Bing later rejected this in favor of a calculation by Arthur Beer for July 6, 1439, the date of the closing session of the Council of Florence, in which the Articles of Union between Eastern and Western Christendom were signed by Latin and Greek delegates. More recent recalculation by Professor John L. Heilbron has independently confirmed this date and even estimated the time of day at about noon.