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    Posted April 8, 2014 by
    aidandavies
    Location
    Alabama

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    Why the World's Longest Straight-Line Sail Isn't Exactly Straight

     
    Let’s say you’re an impossibly intrepid around-the-world explorer with a boat. You’ve done the Atlantic. You’ve done the Pacific. What’s left? What, you might wonder, is the longest distance one can sail in a straight line without hitting land? Unless you have an advance geography degree or very, very advanced spatial skills, you’ll probably be surprised to find that the longest possible straight sail goes from Pakistan to Siberia and it looks like this. Wait, what?

    "Ken,” you are going to say “that’s not a straight line!” Well, it is and it isn’t. You certainly can’t lash your tiller at a certain compass direction and steer along the same course from Pakistan to Russia. In fact, this course requires you to change compass bearing continuously. Look: you’re traveling southwest when you leave Karachi, Pakistan, but by the time you arrive at the chilly Kamchatka Peninsula, you’re heading northwest.

    But this course is a “straight line” in the sense that it marks the shortest path between Pakistan and Russia. (Well, technically, the shortest path would be a similar land route that filled in the “gap” in the arc over Central Asia. But this follows that route in the opposite direction.) Don’t believe me that this is a direct path? Get a globe and a piece of string and try it out. Alternately, watch this video. Did I just blow your mind?

    This kind of path is called a “great circle.” You plot a great circle between two points on a sphere by imagining the plane that would slice through both points and the center of the sphere. The intersection of that plane and the Earth is the great circle. They’re incredibly useful tools in navigation, because they show the shortest distance between two points. Americans traveling to Europe are often surprised to find that they’re going by way of Canada and Iceland. But the outward “bulge” of the Earth if you head due east means that the northerly trip is actually a shortcut

    It’s amazing to me that this particular great circle exists, because it goes almost 20,000 miles without hitting land. That’s about 80 percent of the way around the world. Look how you have to thread the needle between Tierra del Fuego and the Antarctica Peninsula, between Africa and Madagascar, between the Near Islands and the Rat Islands of the Aleutians. If you do want to sail this route, I recommend starting in Kamchatka, to take advantage of favorable west-to-east winds. Watch out for pack ice off Antarctica, and sassy pirates with haunted eyes off East Africa. They might want to be the captain now.

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