What is the most significant (to earth) astronomical event we can expect to observe during our lifetimes?
Supernova? Geomagnetic storm? Bright comet? Asteroid impact? McDonalds turning the moon into an advert?
>>9110921
Define "significant."
Also, are you talking naked-eye observe, or do telescopic observations count?
I'd say the Shumaker Levy 9 impact into Jupiter might count -- it gave us fair warning, though people seem to have by and large decided to ignore it.