Somewhere back in the murky reaches of time, before Frosty met Parson Brown but after reindeer and elves turned Jesus’ birthday into a regular gig, model trains became synonymous with Christmas. Maybe it was the long lines and sharp elbows that made people crave the hypnotic effect of watching a tiny train go round and round. Or maybe, after being cooped up with their relations a little too long, people came to relish the Godzillalike view of the terrain. Whatever the reason, the sight of a baby choo-choo chugging through a miniaturized snow-covered countryside is now part of the holiday spectacle just like eggnog, angels, and boughs of holly. Pulling into Union Station this week, right on time for the yuletide festivities, is the largest portable Scale G model train in the world. Watch it traverse the minimountains and fjords of Norway again and again. Kids can marvel. Grownups can zone out. And the delusional can indulge in daydreams of kicking some Mothra ass. The train’s run begins today at noon at Union Station, 40 Massachusetts Ave. NE. Free. (202) 289-1908. (Annys Shin)