Note however that the Egyptian observation of a slowly changing stellar alignment over a multi-year period does not necessarily mean that they understood or even cared what was going on. For instance, from the Middle Kingdom onwards they used a table with entries for each month to tell the time of night from the passing of constellations. These went in error after a few centuries because of their calendar and precession, but were copied (with scribal errors) long after they lost their practical usefulness or the possibility of understanding and use of them in the current years, rather than the years in which they were originally used.