I will give you four solutions to this challenge, each of which lets you SEE IT for yourself. No need for you to trust or believe science. I’ll SHOW you.

**BUT FIRST, HERE’S AN OFFER: **Bring the $8,250 in cash and fly into Baltimore (BWI). I will pick you up with $17,500 of my own cash (I’m giving you two-to-one odds plus $1,000 to cover your airfare in case I’m wrong and Earth turns out to be flat).

I will drive us down to Deale, Maryland on the Chesapeake Bay and we’ll go out in my sailboat and I will demonstrate “Solution One” to you.

**SOLUTION ONE, NAUTICAL DIPPING: **There’s a centuries-old nautical navigation formula that’s used by sailors in a process called “dipping a lighthouse.” It wouldn’t work if Earth wasn’t round.

**The formula: **1.17 x the square root of the height of your eye (in feet) above the water = NM (nautical miles to the horizon).

**Example: **On a boat deck, your eye is 9 feet above the surface of the water. And you’re looking for a lighthouse, which the chart shows as having a light 100 feet above the water. If you could see the water at the base of the lighthouse, you’d just need to run the formula once.

- Square root of 9 is 3. Plug that into the formula: 1.17 x 3 = 3.51 NM.

But lighthouses are up on land and are tall due to the curvature of the Earth. If the light sat at water height, sailors could be dangerously close to land before it came into view over the horizon. (You’ve heard of a “horizon,” right?)

So you run the formula a second time to account for the height of the light above the water, which is shown on nautical charts, then you add the two distances.

- Square root of 100 is 10. Plug that into the formula: 1.17 x 10 = 10.71 NM.
- Add 3.51 NM + 10.71 NM = 14.22 NM total to the light.
- Then as you approach land, you look in the direction of the lighthouse until the instant you see the light and at that instant you are 14.22 NM from the light.

We will use my GPS to prove this distance. Here’s an exaggerated image.

**If the Earth were flat you could see a Virginia lighthouse from the coast of France if you had a telescope of sufficient power.**

Most people think lighthouses exist to warn sailors so they won’t crash into the shore. But the primary use for them was to determine an exact distance to the shore as old ships approached. At the instant of the first “dip” of the light, they got a precise distance fix right when they most needed it.

Dipping is also useful for coastal sailing so the boat can constantly check its distance from land.

**SOLUTION TWO, YOU DON’T NEED A BOAT: **If you don’t have $8,250 plus airfare to lose, you could do this on your own in an ocean front hotel before you bring me your money.

Ride the elevator to the top floor and spot the base of some distant object that is right on the horizon on the water. Check a map to find the distance to that object.

Run the formula based on your height above the water in the hotel, which will confirm the formula.

Now take the elevator to the lobby, walk out front and notice that you no longer see the object.

**If the Earth were flat, you see exactly the same amount of the object from the shore or from the top of a 20-story hotel.**

**SOLUTION THREE, NO MATH NEEDED: **I’m a former U. S. Air Force pilot and I’ve flown USAF jets high enough to see the curvature of the Earth. Too bad the Concorde is no longer flying because you could sip champaign while seeing it from a passenger seat window.

But you can still get up there and see for yourself!

Several companies offer rides in former military jets. Google around and find one, call them, and tell them you have $8,250 to spend. They’ll rocket you up to where the sky turns purple, then dark purple, then goes black. And you’ll see the curvature.

**SOLUTION FOUR, THE BEST: **But soon, for a few million dollars, even YOU will be able to undeniably see the curvature of the Earth, once Space X, et al, finally gives us private space rides. As you rise into orbit around the Earth, you’ll finally get it. Undeniably get it. Undeniably.

**BUT I WANT THAT PRIZE MONEY: **Rather than blow $8,250 on a jet ride, just bring it in cash to BWI. We’ll hire a “second” (maybe an off-duty police officer, anyone we both would trust) who will hold the cash to ensure my prize money won’t run away once I prove it. That extra cash would offset my sailing expenses for the coming season, when I’m out dipping lighthouses on the Chesapeake.

I gotta be honest, though: The jet ride would be a LOT more fun. And if you’re not passed out or puking the whole time, you’d see the curvature yourself.

**EARTH IS AN OBLATE SPHEROID:** I offer this closing comment just in case this is a trick question. The truth is that the Earth is NOT, in fact, spherical. So, in that sense you are absolutely correct. If the $8,250 prize is to be awarded to someone who proves “the Earth is a sphere,” well, no one would collect because the Earth is, in fact, an **“oblate spheroid.” **It is not a true sphere.

Because the surface of the Earth is spinning at just over 1,000 miles per hour, the centrifugal force causes it to bulge at the equator. The Earth is 24,874 miles in circumference if you measure the length of the equator. But it is 24,860 miles if you measure the circumference through the poles.

I was on the equator several times this month and I could see the bulge. (Just kidding about seeing the bulge, though I was on the equator.)