PART THE FIRST. In Which the System Is Set Up:
We know that BTTF takes place somewhere in California–and for the sake of argument, we’ll say that Hill Valley is near Los Angeles, hence at ~35o N latitude. It’s October 26, meaning that it’s autumn in the northern hemisphere, and so for our calculation we’ll take the Earth’s distance from the sun to be roughly perihelion, and unchanged during the minute time jump.
According to Doc’s watch, the time-jump starts at 1:20A.M. Now, the Earth rotates 360o every 24 hours, a rate of 15o per hour. If we assume that Hill Valley was furthest away from the sun at midnight local time, it’s therefore rotated (counter-clockwise, as viewed peering down from the North Pole) exactly 20o since midnight. Here’s a summary of what’s going on at the moment Einstein makes his temporal leap: