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## November 3, 2016

### Even for Earth-crossers, the chances of hitting Earth are extremely small, and here’s a way to see why.

**Make a circle with your left thumb**and forefinger to represent the orbit of the Earth around the Sun – an imaginary dot in the centre of the circle of your thumb and forefinger.

Then link it with a circle of your right thumb and forefinger, representing the orbit of a killer asteroid. Now imagine the circle of your left hand changing from fingers to a filament 1/100 the diameter of a human hair, representing the path swept out by Earth. And imagine your right-hand fingers shrinking to a filament 1,000 times thinner than the left-hand one, representing the path of the asteroid.

Only if those hairs pass through each other is there any chance of an impact, and since impactor orbits move around in time, there is a chance of an impact only for a short time, before the hairs no longer intersect. And even if the orbits do intersect briefly, there is only a tiny window of time, a few minutes at most, in which both impactor and Earth are at the intersection point at the same time – otherwise, no impact. For any given asteroid or comet, the chance of impact is extremely small. How chance and probability affect the path of Big History | Aeon Essays

Posted by gerardvanderleun at November 3, 2016 9:59 AM. This is an entry on the sideblog of ** American Digest: Check it out.**