Nationals Park will become a playoff site if Washington keeps its lead. (Greg Fiume/GETTY IMAGES)

It’s almost September, and the baseball pennant races are heating up. Washington fans might need a refresher course on pennant races. After all, no Major League Baseball team from Washington has played a post­season game since the Senators lost the World Series in 1933.

Even the team closest to Washington, the Baltimore Orioles, haven’t made the playoffs since 1997. (The Nationals’ manager, Davey Johnson, was in charge of that team.)

This season, the Nats are definitely in the playoff hunt. After Tuesday’s games, the Nats lead the National League East Division by four games over the Atlanta Braves.

Here’s what you have to know to stay on top of the race:

The basics: Five teams from the National League and five from the American League make the playoffs.

Chipper Jones of the Atlanta Braves rounds the bases after hitting a home run. The Braves are the Nationals only competition for the National League East division. (Scott Cunningham/GETTY IMAGES)

There are two ways to get in. First, the teams that finish in first place in each league’s three divisions make it. The two remaining teams that have the best record in each league also make it as “wild cards.”

It’s important for the Nats to win their division because the two wild cards in each league will play a winner-take-all game to stay in the playoffs. Even if the Nats were to win the wild-card game, they would have used one of their best starting pitchers, meaning he wouldn’t be able to play in one of the first division playoff games.

It’s called a pennant race because the winner of the National League and American League playoffs get to fly a pennant, or flag, above their stadiums.

Check every day: Baseball games are like school days: There are lots of them. So you have to check the Sports section or look online almost every day to see how the Nats did the night before.

Better yet, get your homework done and ask your parents if you can stay up and watch some of the games on TV. When the races are tight, every game is important. Last season, the Boston Red Sox and Atlanta Braves looked likely to make the playoffs, but both lost out on the season’s last day!

Check the other teams: The Nats are in a race with the Atlanta Braves. When the Braves lose, that’s almost as good as a Nats win. (The Nationals add a full game to their lead every time they win a game and the Braves lose one; the reverse is also true.)

The magic number: This sounds like something out of Harry Potter, but it’s simple math. In the last few weeks of the season, you’ll hear about the magic number. It will be the combined number of Nationals wins and Braves losses needed to clinch a division title for the Nationals.

And once the Nats make the playoffs, it won’t be crazy to talk about the World Series. Washington in the World Series? That would be magic!

Fred Bowen writes the sports opinion column for KidsPost. He is the author of 18 sports books for kids.