Robert explained, “Since the earth moves in a giant ellipsis around the sun each year, you'd assume that you’d never technically be in exactly the same spot in Space except for on one single day each year, right?”
Brianna nodded,“OK, I'm following.”
“The truth is, a completely different person can stand in the same exact spot one year later and not ever stand in the same 'spot’ in the universe that he or she occupied last year.”
“Why not? That doesn’t make sense.” Brianna interjected. “Wouldn't the planet have made a full rotation again back to the same location?”
Robert grabbed a pen from his desk drawer and busily drew a circle on a fresh sheet of paper. He quickly illustrated how the Earth moved elliptically around the Sun. The picture appeared as a plate might, tilting at a slight angle. Turning back to Brianna, he finally replied, “It’s nuanced concept, actually. The true scenario is vaguely similar to the picture I drew but infinitely more complex. Our planet revolves around the sun at about 18.5 miles per second. That’s this first smaller circle I drew here,” he said, tapping the paper. “But our entire solar system itself – the ‘plate’ itself – also rotates around the center of the Milky Way galaxy at roughly 140 miles per second. The Earth’s rotation around the sun is not on the same plane (or tilt) as that of the rotation of our solar system around the Milky Way. So it’s not like we just add our speed around the Sun to our speed around the Milky Way galaxy. It’s a proportion of the two. And if you can believe it, the entire Milky Way galaxy also moves around another local cluster of galaxies at about 25 miles per second on its own special tilt. Imagine these rotating gears, if you can think of them like that – all of different sizes, all spinning on unique axes, and all with disparate velocities – each circling something bigger than themselves. It’s kind of like that picture of the atomic energy symbol.”
Brianna’s face scrunched up as she vaguely recalled the graphic for the “atomic whirl”.
“Even if you came full-circle on earth's orbit, that won’t mean that a year later you would be in the same spot in our solar system's rotation around the Milky Way, or the same spot in the Milky Way’s path around our local cluster of galaxies, for that matter.” Robert ended with, “When you add up the collective proportional speeds of our rotating planet, solar system, and galaxy, it can be quite a bit more than you’d imagine – even if you never normally notice it. You are speeding through Space much faster than just the velocity of the planet you are on.”