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ANDREA SEABROOK, host:

Let's go even further back now - to the year 55 B.C. Rome's Julius Caesar was at sea about the invade Britain. Caesar's log of his voyage was pretty detailed. He noted the tides, the full moon and the approach of the autumn equinox. One thing we don't know - a question that scholars have argued over for literally centuries - is the exact date Caesar landed in Britain.

Sounds like history but it's today "Science Out of the Box."

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SEABROOK: Caesar's quest became a personal quest for Donald Olson. He's a physics professor at Texas State University. Olson and his colleague Russell Doescher now say they've nailed down the date Caesar landed in Britain and they're going against the current of conventional wisdom.

Professor Olson says for a long time there have been two conflicting scenarios for Caesar's arrival.

Professor DONALD OLSON (Physics, Texas State University): The historians say Caesar approached Britain near the white cliffs of Dover on August 26 or August 27 of 55 B.C. He chose not to land there because the cliffs are a very bad place to land with Britain warriors at the top throwing missiles down.

SEABROOK: Yeah.

Prof. OLSON: So, if he follows the afternoon title stream, the history books will say that the title occurrent or title stream carried Caesar and the Roman fleet to the northeast of Dover.

SEABROOK: Okay.

Prof. OLSON: But every scientist, and that would be astronomers and so-called hydrographers - which means tidal experts - they all say, no way, cannot be true - they make very strong statements - 'cause on August 26 or August 27, 55 B.C., they say the afternoon tidal stream was running nearly full strength in exactly the opposite direction to the southwest of Dover.

SEABROOK: I love this. It's like an epic battle between historians and scientists.

Prof. OLSON: It goes back and forth. A scientist says southwest; historian says no, northeast.

SEABROOK: Okay. So, you undertake this exercise, and it's not just an academic one. You, Professor Doescher and your honor students went out on a boat trip to…

Prof. OLSON: Yes, we did.

SEABROOK: (unintelligible).

Prof. OLSON: And what we did, we realized maybe five or six years ago, we realized that August of 2007 would provide an almost unique opportunity. The sun and the moon would be in the same position - the distance of the moon, the phase of the moon, the time of year, the celestial coordinates of the sun and moon - would be almost identical to what they were back in late August of 55 B.C. So, we actually did experiments near Dover for about a week.

SEABROOK: What did you do exactly?

Prof. OLSON: Well, we took the boat out to the spot a little ways out in the channel, just off the cliffs, about where Caesar describes being, we cut the engine and let the boat drift with the tidal stream. It's really hard to tell which way you're drifting when you're in the water. It really is - but we had recording GPS so we could track exactly what direction we were moving and how fast we were moving in the boat.

SEABROOK: And which direction was it?

Prof. OLSON: On the conventional date, the tidal stream - we have shown from theory and from our experiment - was running exactly the wrong direction.

SEABROOK: Okay. Now, let's step back for just a quick second. Your specialty is examining this kind of quandary, correct?

Prof. OLSON: Yes, it is. I teach an honors course called "Astronomy in Art, History, and Literature." When you get to graduate school, you get very specialized. And my specialty, oddly enough, was Relatively Theory. What I like about these problems is now I get to think again about art. The night sky paintings of Van Gogh and literature - descriptions of the sky and writings by Shakespeare, Walt Whitman, Lord Byron, and others.

So, it enriches my life to be able to try to apply science to the humanities.

SEABROOK: So, Professor Olson, when did Caesar land in Britain?

Prof. OLSON: According to our calculations, he must have landed on August 22 or August 23 of 55 B.C., dates that are four days earlier than the conventional picture.

SEABROOK: Tada.

Prof. OLSON: On those dates - August 22 or 23 - the tidal stream would carry him to the northeast. The topography fits the ancient accounts and all things fall into place.

SEABROOK: So, Professor Olson, I have to ask: four days' difference?

Prof. OLSON: Yes.

SEABROOK: What does that matter much?

Prof. OLSON: Because this is in a sense the beginning of British history. And it's of some interest to know when it began. But what's really probably more interesting is where did Caesar land? Where did British history begin? And with our solution for the date, we now can say that we know where Caesar landed and it is the place where historians had wanted him to land all along.

SEABROOK: Donald Olson, he's a professor of physics at Texas State University at San Marcos. His team's article recalculating the date of Julius Caesar's British invasion is in a current issue of Sky & Telescope magazine. Donald Olson, thank you so much.

Prof. OLSON: Oh, thank you.

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