I'd go back to September 10, 2001 to stop Bush from doing 9/11.
protective bubble, no interaction? the big bang.
It'd be easier to track down winning lotto numbers and get instant money.
Wouldn't it be funny if Jesus was a actually a bastard, the result of some whore having an affair with another man that rationalized the birth as an "immaculate conception" from god to expain her swollen belly to her husband? Only one way to find out.
Rules: Can only travel to past, not forward. No interaction, imagine viewing from a "protective capsule" in the sky.
I'd go watch something epic like the Fall of Persia, Jerusalem, Carthage, Stalingrad, Gettysburg, Hastings, Little Big Horn, etc. Maybe go see the Aztec reactions when Cortez showed up or watch the fall of that empire.
I went "back in time" to 8:57 yesterday and bolded the rules in the OP.
Dammit! And that broke the rules.
Formation of the moon is a good one, on that note I'd REALLY love to see mars back when it might possibly have been a fertile blue planet.
Rome would be a great thing to study, as would the American wars.
On that note, is the Trojan horse real? I'd find out.