But that kind of a jump isn't unprecedented, historically. The Brewers made the league switch in 1998, while the Tigers jumped from the AL East to the Central that same season to fill the void left by Milwaukee.
"You just don't know the other league as well as you know your own league," said Phil Garner, who managed the Brewers to a 74-win season in their first year in the NL -- four fewer wins than the previous year. "No matter how many scouting reports you have, there's still a little bit of a comfort factor having seen players."
Garner noted the transition should be much easier for Houston in 2013 because of the available scouting technology and the presence of constant Interleague Play.
Following the switch, the biggest difference for Garner was the club adjusting its roster philosophy. In the AL, teams often sign players expecting to use them as designated hitters. National League squads, on the other hand, typically have benches littered with solid pinch-hitting options that can play many positions.
The '97 Brewers -- then in the AL -- didn't have an everyday DH (they signed Julio Franco to DH in August, but until then the lineup spot was a platoon). Still, in '98, every time John Jaha -- who had DH-ed almost as much as he played first base in '97 -- was in the lineup, it meant he was also in the field.
"You have to build your club differently when you have a DH," said Garner, who is currently a special advisor for the A's. "In the National League, you're going to be pinch-hitting, but it's just different with the DH."
The Astros are a young team that doesn't exactly have a DH prototype -- a veteran with some pop who may be slowing down in the field.
"We need to decide what our strategy is going to be for the DH position," general manager Jeff Luhnow said. "Do we have anybody internally that can compete, or do we have to go out and sign somebody? Do you use that as a platoon or do you use it for a slugger/RBI guy? We're going to look at all kinds of alternatives. I'm actually kind of excited about doing that. I've never had to do that before."
Luhnow will have to adjust his entire approach because of the league switch. There are already reports that the club is considering bringing back Lance Berkman, who would seem to fit that position perfectly. Had the Astros remained in the NL, it's likely they wouldn't have had the room to pursue Berkman.
For the '98 Tigers, switching divisions didn't bring much change, aside from new matchups. They finished in last place with 65 wins in their first Central season -- after finishing with 78 victories in '97.
However, for fans, there were some big adjustments that had to be made. In the '80s and early '90s, the Blue Jays and Tigers developed a solid AL East rivalry, finishing 1-2 in the division three times in a span of eight years. That rivalry was highlighted by an epic 1987 pennant race that came down to a final-weekend series in which all three games were decided by one run. The Tigers won on the final day.
By moving to the Central, the Tigers had to develop new rivalries with the Twins, White Sox and Royals. (They played with the Indians until realignment in 1994.) Gone were the days of Tigers-Blue Jays, Tigers-Yankees and Tigers-Red Sox divisional matchups.
For Houston, it's a bit different in terms of rivalries. The Astros are walking right into one by heading to the AL West, home of their intrastate rivals, the Texas Rangers.
"I think our fans are looking forward to seeing the Rangers and developing that rivalry a little bit more," Luhnow said. "... It's a tough division, but if you're going to win you've got to beat everybody, so you might as well get trained in the toughest division in baseball."
Before '98, the last time a division switch took place was in 1972, when the Washington Senators became the Texas Rangers and headed to the AL West, while the Brewers came East.
The results were similar, as both teams finished in last place. The Brewers won four fewer games than the year before, and the Rangers won a measly 54 -- though the Senators' 63 wins in their final season in D.C. didn't exactly put them in any pennant races.
If you've been counting, that's four teams that have switched divisions since baseball went to a divisional format in 1969 -- and three last-place finishes. All four teams saw their win totals drop, and two of them were fairly significant decreases.
But it isn't a total negative for teams to switch divisions. In 1993, essentially every team in the Majors changed to a new division, because the league opted to realign from two to three in each league. That meant new opponents and new divisional rivals for everyone.
But the Atlanta Braves were the only team to play in an entirely new division, with none of the teams from their old division remaining. How did they fare after the switch? Well, they were 22 games above .500 when the strike hit in 1994 and went on to win each of the next 11 NL East titles, until the Mets took the crown in 2006.
Success in a new league or division is by no means impossible, and, naturally, it ultimately comes down to talent.
"The Astros are at a little bit of a disadvantage by switching divisions," Garner said. "But I just think that over the years, the difference has gone away."
Still, there's no doubt the Astros -- and their fans -- are in for a few adjustments both before and during the 2013 season.