Jack Aubert, Your question was : 'Why the earliest sunset is at 13 dec'?
Only looking to the aspect of the declination of the sun in december the length of a day wil shorten so the sun will set earlier each day till about 21 december. From then the length of the days will increase. In this periode the difference in the time of the sunset each day however is smaller than one minute. From about 12 or 13 december this difference is even smaller than 30 seconds and still decreases till zero at about 21 december. (this also depends on the latitude you live) But we also have to consider the equation of time. In december the difference in the equation of time is about 30 seconds each day and this means that, only looking for this aspect, the sun sets 30 seconds later than the day before. Not the value of the equation of time is relavant, but the difference each day. When we sum these 2 aspects we see that from about 13 december the sunset will be later than the day before. For the same reason during some days after the winter begins the sun rises later than the day before. Fer de Vries. [EMAIL PROTECTED],nl
