There isn't a National No-hitter Day, but if we did have one, today would be worthy of the honor.

While more than 300 no-hitters are officially recognized by MLB, the most on any calendar date is six, with four dates sharing this distinction, according to the Elias Sports Bureau.

April 27 marks the first of them, along with May 15, Sept. 20 and Sept. 28. Here's a closer look at the no-hitters that have taken place on these four dates.

April 27

2003: Kevin Millwood, Phillies
2002: Derek Lowe, Red Sox
1994: Scott Erickson, Twins
1973: Steve Busby, Royals
1968: Tom Phoebus, Orioles
1944: Jim Tobin, Boston Braves

Millwood and Lowe threw no-hitters on April 27 in consecutive years. Lowe’s no-no was the first at Fenway Park since 1965 (Dave Morehead), and it capped an impressive April for the right-hander, who ended up finishing third in the American League Cy Young Award voting after going 21-8 with a 2.58 ERA.

Erickson’s no-hitter came after the right-hander had allowed 38 hits and 18 earned runs over 21 2/3 innings in his first four starts of 1994. He finished the campaign with a 5.44 ERA and a 1.61 WHIP in 144 innings.

Making just the 10th start of his career, Busby was effectively wild in his no-hitter on April 27, 1973, issuing six walks. He averaged 264 innings per season from 1973-75 (3.54 ERA) and threw another no-hitter in 1974, but his career was stalled by a shoulder injury. In 1976, Busby became the first known pitcher to undergo rotator cuff surgery. The procedure was completed by Dr. Frank Jobe, who also performed the first Tommy John surgery in 1974. Busby returned in 1978 but only threw another 158 innings in the big leagues with a 4.84 ERA.

May 15

1981: Len Barker, Guardians
1973: Nolan Ryan, Angels
1960: Don Cardwell, Cubs
1952: Virgil Trucks, Tigers
1944: Clyde Shoun, Reds
1915: Claude Hendrix, Chicago Whales

Barker fired the 10th perfect game in Major League history on May 15, 1981, striking out 11 batters against the Blue Jays. Barker would make the AL All-Star team the same season, but he never earned another All-Star selection in his 11-year career. Overall, Barker went 74-76 with a 4.34 ERA.

Cardwell's no-hitter came in his first game after being traded from the Phillies to the Cubs. It made him the first pitcher since at least 1901 to throw a no-no in his first game with a new team, not including pitchers making their big league debut. The feat has since been accomplished by Wilson Alvarez with the White Sox in 1991 and Hideo Nomo with the Red Sox in 2001. (Mark Langston was part of a combined no-hitter in his first game with the Angels in 1990.)

May 15 is also the date on which Ryan threw the first of his record seven no-hitters. The hard-throwing righty struck out 12 Royals in the gem. It wouldn’t be long before Ryan recorded his second no-no, which came exactly two months later on July 15, 1973.

Ryan and Trucks are two of the six pitchers who have thrown two no-hitters in the same season, along with Johnny Vander Meer, Allie Reynolds, Roy Halladay and Max Scherzer. The first of Trucks’ no-hitters came on May 15, 1952, against the Washington Senators. He threw his second on Aug. 25. The two gems were the highlights of a year in which Trucks went 5-19 with a 3.97 ERA.

After Tobin threw his no-hitter on April 27, 1944, he was the losing pitcher in Shoun’s no-no 18 days later. Shoun was making his first start of the season after previously appearing four times in relief for the Reds.

Sept. 20

1969: Bob Moose, Pirates
1958: Hoyt Wilhelm, Orioles
1908: Frank Smith, White Sox
1907: Nick Maddox, Pirates
1902: Nixey Callahan, White Sox
1882: Larry Corcoran, Chicago White Stockings

Moose’s no-hitter was part of a brilliant second half in which he recorded a 1.55 ERA over 87 1/3 innings. After fighting back from career-threatening surgery to remove a blood clot under his right arm, Moose died tragically in a car accident on his 29th birthday in 1976. He spent his entire career with the Pirates, posting a 3.50 ERA.

Wilhelm was a reliever for almost all of his Hall of Fame career, but he made 10 starts in 1958 and threw a no-hitter in his second-to-last outing of the year. The knuckleballer was 36 years old at the time. Wilhelm made a career-high 27 starts the next season and notched a big league-leading 2.19 ERA over 226 innings, but he started only 15 games in 13 seasons after that.

On Sept. 20, 1882, Corcoran became the first pitcher to throw multiple no-hitters. His first, on Aug. 19, 1880, was just the fourth official no-hitter in Major League history.

Sept. 28

2014: Jordan Zimmermann, Nationals
2012: Homer Bailey, Reds
1975: Vida Blue, Glenn Abbott, Paul Lindblad and Rollie Fingers, Athletics
1974: Nolan Ryan, Angels
1951: Allie Reynolds, Yankees
1884: Ed Cushman, Milwaukee Cream Citys

Zimmermann’s no-hitter came on the final day of the 2014 regular season and is best remembered for the sensational diving catch Steven Souza Jr. made in left field to seal it. Zimmermann finished fifth in the NL Cy Young Award race that year, as he posted a career-best 2.66 ERA.

On the same date two years earlier, Bailey no-hit the Pirates in a 10-strikeout gem. Bailey fired another no-hitter on July 2, 2013, marking just the seventh time in history that two no-hitters were thrown by one pitcher without another hurler doing it in the time between them.

The previous two times both involved Ryan, who threw consecutive no-hitters in 1973 (see above) and again over the 1974 and 1975 seasons. Ryan fired his third career no-no on Sept. 28, 1974, striking out 15 and walking eight, and he followed it up with his fourth on June 1, 1975. Coincidentally, Reynolds also accomplished the feat, with his no-hitter on Sept. 28, 1951, coming after he threw one on July 12 of the same season.

After Ryan hurled four no-hitters for the Angels in the span of two-plus years, the Halos were on the losing end of a combined no-no against the A’s on Sept. 28, 1975, the final day of the regular season. Having already clinched the AL West crown, Oakland pulled Blue after five hitless innings, and Abbott, Lindblad and Fingers finished it off. Blue previously no-hit the Twins in 1970, making him the first pitcher to be involved in a regular no-hitter and a combined one.