Comets and the distance scale of the solar system

Posted by David Eicher
on Monday, June 17, 2013

Comet Hale-Bopp // Michael Stecker
Here’s a comet exercise of the day, one that will help you appreciate the scale of the solar system. Take a ruler and mark 1 centimeter on a sheet of paper. That’s the distance between the Sun and Earth, 1 astronomical unit (AU), or about 93.0 million miles (149.6 million kilometers) — vastly farther than we have ever traveled in space as humans. You could also add other planets, too — Jupiter at 5 AU, Saturn at 9.5 AU, Uranus at 19 AU, and Neptune at 30 AU.

Now consider that on this scale, the Kuiper Belt exists between 30 and 50 AU, 30 and 50cm, and that the inner edge of the Oort Cloud begins 220 “yards” from the Sun. On this scale, the outer edge of the Oort Cloud, the “edge of the solar system,” would stretch 1,000 yards away from the Sun — a distance of 10 football fields end to end, with the distance between Earth and the Sun as just 1cm. The distance to the Oort Cloud’s outer edge represents 40 percent of the distance between the Sun and the nearest star system, Alpha-Proxima Centauri.

So when someone says confidently that they will be traveling from star to star, leisurely exploring the Milky Way in a spacecraft, you can begin to get an appreciation of why they very likely will never do that, regardless of technological improvements, simply because of the immense distance scale of the cosmos, even to the outer part of our own solar system or to the closest star to the Sun.

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