When Barack Obama steps forward Tuesday to become the 44th president of the United States, it will be a momentous event for bunches of reasons, and one is that it will be the most-watched presidential inauguration in American history.

Some of that is the man and the times, and some is the simple math that more screens - from TVs to computers to phones - will be broadcasting the moment to more people than ever by a massive margin.

More than 71 million people watched TV news coverage on election night, and millions more connected online, according to Nielsen Media Research. The highest-rated inaugural was Ronald Reagan’s 1981 ceremony that drew almost 42 million.

Considering the election-night numbers, the huge growth in news coverage and the explosion of online sources, some predictions are that the number of people watching will be almost double that figure.

By the way, for the timing of it, the inaugural ceremony is scheduled to start at 11 a.m. Tuesday. The president’s term starts at noon on Jan. 20, by order of the 20th Amendment to the U.S. Constitution, so President Obama is scheduled to take the oath then and he’ll give his speech right after that.

All the news organizations will have coverage running through the day, generally starting at 6 or 6:30 a.m. Most will also stream on their Web sites for people watching at work, and broadcasts will be available in some cities in places ranging from movie theaters to Starbucks.

Tuesday evening, all the major broadcasters with news divisions will have inaugural specials, and the cable screamers will do their histrionic best through the day. NBC, meanwhile, will show “The Biggest Loser: Couples,” and I’m going to resist the urge to do a political joke here.

Even with all that, there are still a couple of notable connections on each end of the scale. “The Daily Show With Jon Stewart” will be blogging the inauguration live (at www.indecision2008.com). Just in case you want comedy. For substance, PBS’ “Frontline,” TV’s best documentary unit, has a one-hour look at the personal and political paths of Obama (at 10 p.m.).

Inaugural addresses haven’t come with great expectations in a long while, but for many Americans, this year is different. That’s partly because Obama will become America’s first African-American president, and partly because these are such difficult times.

Whether Obama plays it safe and talks policy, or rises up to deliver a speech to match the history, this inauguration is exactly the kind of moment meant for television. It’s an experience to be shared with the rest of the country, and for now anyway, there’s no other medium, no other place, where you get that feel.

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And then there’s that other big event this week. It may fall a bit short of the historical impact of an inauguration, but the return of ABC’s “Lost” - in bracing, exhilarating style - on Wednesday is a momentous event for fans.

Season 5 (at 9 p.m. Wednesday) starts with a rush, and a few answers that, of course, raise more questions. But we’ll learn in the first few minutes that our biggest question isn’t, Where is the island?

Viewers get told early that the island is skipping through time, due to an energy source there that’s almost limitless. Apparently, the flashbacks and flashforwards are gone, at least for a while, because the central stories have enough jumping around in them. “So when are we now?” Sawyer asks at one point. That, my impertinent friend, is precisely the question.

We’ll also learn that the Oceanic 6 doings we’ve been watching are happening three years after they left the island. Maybe. I could be wrong. We also learn that it seems to be very, very important that all of them go back.

Beyond that, I’m not saying. I’m not sure I’d be right, anyway, but I can tell you this show seems to just keep getting sharper. There’s no stalling, no wasted motion, no avoiding an answer simply to keep the mystery going.

This season has enough mysteries to propel this show at rocket speed, and “Lost” is, as always, a thrill ride that’s as full of adrenaline as it is smarts. Oh, and Vincent the dog is still fine.

Here’s more of What To Watch (or Not) this week.

Wednesday:

“Lie to Me” (8 p.m. on Fox): Tim Roth plays an expert on reading faces, bodies and voices to tell if people are lying, and he works with cops to solve crimes. Yes, this does sound familiar, but it’s a solid, if not spectacular, procedural, and its biggest downside is it’s on opposite “Lost.”

“Top Chef” (10 p.m. on Bravo): It’s the hour everyone loves. Time for Restaurant Wars, and they’re on the streets of New York, no less.

Thursday:

“Burn Notice” (10 p.m. on USA): This sassy, intelligent, thoroughly entertaining show is back, and picks up with Michael looking to find who tried to kill him. It’s one of TV’s most engaging series, and for people who haven’t seen it, you can pick up the story thread easily enough.

Sunday:

“The Last Templar” (9 p.m. on NBC): The two-part miniseries is a little bit “National Treasure” and a lot more “The Da Vinci Code.” Mira Sorvino is an archeologist who, of course, reluctantly teams with FBI agent Scott Foley to track down the secrets of the medieval Knights Templar after a mysterious device is stolen from a museum. It concludes Jan. 26.