Daniel notices something. September, October, November, and December sound like they mean seven, eight, nine, and ten. But they are the ninth, tenth, eleventh, and twelfth months.

He wants to know why.

The names are a fossil. The Roman year once started in March. September was the seventh month. October the eighth. When the calendar changed, the names stayed.

The reason there are twelve months comes from the Moon. There are a little more than twelve lunar cycles in one solar year, so calendars built around lunar cycles naturally tend toward about twelve months. But twelve lunar months do not make a full solar year. That mismatch between the Moon and the Sun is one reason calendars have needed adjustments for thousands of years.

Julius Caesar addressed the problem in 46 BC, apparently with help from the Alexandrian astronom ...