My Coffee Cup is Moving – Relatively

CoffeeCupThis is my morning coffee cup.

It rests quite securely next to my keyboard.

Then I realized that the earth is actually rotating, so the coffee cup is actually flying along around the earth, with me and the whole house. How fast? At the equator, a point moves at a speed of 1070 miles per hour. That’s faster than the cruising speed of an airliner. It’s slower here in San Diego, since we’re farther north. Using the cosine of the latitude, I resolved that the speed of my coffee cup at my desk is actually “only” 789 miles per hour.

Of course, the whole earth is moving around the sun, once in a year. It turns out that the speed of the earth around the sun is 67,000 miles per hour. Almost a hundred times faster. So my cup is not really describing a circle as it spins around the earth, it actually describes a very stretched spiral, as it hurls around the sun.

But wait, our sun circles around the disk of the Milky Way galaxy. The sun is about 26,000 light-years from the center, and it takes about 200 million years to go around once. Interestingly, it’s only gone around the center of the galaxy about 20 times since the sun formed. At the beginning of the last “galactic year” about 200 million years ago, the first dinosaurs arose. Two thirds through that last galactic year, the dinosaurs were wiped out.

The exact speed of the sun around the galaxy is actually still debated and argued among scientists much more educated than I am. My simple math, however, says that based on those assumptions, the sun is moving around the center of the galaxy at a speed of 486,000 miles per hour.

So my cup is making a stretched spiral inside a very stretched spiral as the sun circles the galaxy.

Our galaxy, along with the local group of galaxies, is also moving. From where it is moving is hard to determine – perhaps the origin of the universe. But it is moving at an estimated staggering 2.23 million miles per hour. Which makes the sun’s circle around the galaxy just a stretched spiral, as the galaxy races away from the origin of the universe.

My coffee cup is moving, as a stretched spiral in a stretched spiral in a stretched spiral at a speed of about 2.23 million miles per hour, a speed that would get me from here to the moon in about 5 minutes.

It just took me about one minute to proof-read this post, which means I have moved 37,000 miles from where I was before I started, give or take.

On the galactic scale of things, this coffee cup is really buzzing.

Now for a sip of morning coffee.

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