With nine NHL games, three NBA games, an NFL game and an MLB playoff game — made possible by the Chicago Cubs’ victory in Game 4 of the NLCS on Wednesday — Thursday is your (first) sports equinox of 2017.

What’s a sports equinox? As my former colleague Reuben Fischer-Baum wrote on a couple of occasions, it’s when all four major U.S. sports leagues — the NFL, NBA, NHL and MLB — play at least one game on the same day. Historically speaking, it doesn’t happen often. There have only been 17 sports equinoxes in history, including Thursday:

Another sports equinox is in the books Dates on which all four major U.S. sports leagues (MLB, NBA, NFL and NHL) had at least one game NUMBER OF GAMES DATE DAY MLB NFL NBA NHL Oct. 17, 1971 Sun 1 (WS Game 7) 12 3 6 Oct. 15, 1972 Sun 1 (WS Game 2) 12 3 6 Oct. 22, 1972 Sun 1 (WS Game 7) 12 3 5 Oct. 14, 1973 Sun 1 (WS Game 2) 12 3 5 Oct. 21, 1973 Sun 1 (WS Game 7) 12 3 5 Oct. 15, 1978 Sun 1 (WS Game 5) 13 5 5 Oct. 14, 1979 Sun 1 (WS Game 5) 13 3 7 Oct. 12, 1980 Sun 1 (NLCS Game 5) 13 4 8 Oct. 19, 1980 Sun 1 (WS Game 5) 13 3 6 Oct. 27, 1985 Sun 1 (WS Game 7) 13 1 5 Nov. 4, 2001 Sun 1 (WS Game 7) 13 7 4 Nov. 1, 2009 Sun 1 (WS Game 4) 12 7 4 Nov. 2, 2009 Mon 1 (WS Game 5) 1 5 3 Nov. 1, 2010 Mon 1 (WS Game 5) 1 3 3 Nov. 1, 2015 Sun 1 (WS Game 5) 12 7 5 Oct. 30, 2016 Sun 1 (WS Game 5) 11 7 8 Oct. 19, 2017 Thu 1 (NLCS Game 5) 1 3 9

Amazingly, there was a 15-year period without a single sports equinox, between 1985 and 2001. And after 2001, seven more years passed without it happening. But sports equinoxes have occurred much more frequently in recent years — six have happened in the nine years since 2008. They might become even more common in the future, thanks to Thursday-night NFL becoming a fixture, the World Series often running later than usual, and a new NBA scheduling policy this season that moved the season’s opening night up by a week and a half.

If the Cubs can force Game 7 in the NLCS, Sunday will be another sports equinox. As will Oct. 29, if Game 5 of the World Series takes place. But even if those do happen, Thursday’s equinox will be the only one this season with the added bonus of college football — there are two FBS games tonight, including No. 25-ranked Memphis at Houston (A “Super Equinox”?). Good luck finding enough screens to watch it all!