Any year, as the leagues kept it.

Perihelion — the single fullest day of the year, the most games played at once. Equinox — all four major leagues play the same day; a Super Equinox adds college football. (Only possible once all four majors exist.) Total Eclipse — the Equinox's opposite: a dark day inside the season when all four majors are idle at once, like the All-Star break. (Also only once all four exist.) First / Last Light — a league's season opens or closes. The Turn — the midpoint of a league's offseason, marked where its seasons change over. Each league is only drawn in the years it existed, so the wheel thins as you travel back toward baseball's lone early seasons — and the winter toggle re-anchors the wheel to Aug–Jul so a whole winter season reads as one arc.