I hypothesize that it is because we can predict the astronomical days centuries in advance, which in particular means that we can print calendars with &quot;start of $SEASON&quot; days on them with no fear that weather or something will contradict them.<p>I live in Michigan, which has a highly unstable climate. In practice as it happens right now, we&#x27;re really more in &quot;late Fall&quot; than what we&#x27;d usually call &quot;winter&quot;. Other years, winter has come in early November. Only the astronomical events are predictable in advance.<p>I offer as evidence the fact that the primary place I encounter these dates is on calendars. And once they are there, I think we have very little left to be explained; trusting words that appear to source from an authority even over the direct personal experience of our own eyes is a very common problem.