22 July 2009


regular readers know that my interests include the natural world, aviation, music/art, social justice, and astronomy/cosmology (along with much else). today i spotted a NYTimes article about a possible comet strike on the planet jupiter, leaving a bruise the size of the pacific ocean near jupiter's south pole. jupiter's vast size (its diameter is roughly equal to 12 earth diameters) reminded me of a problem in perspective which i encountered while i was a teacher of math, science and environemental studies. i wanted one of my classes to devise a physical scale model of the solar system -- but one quickly realizes that a choice has to be made, for there are really two comparisons to think about. one model could show the sun and planets in true size-comparison to each other (using miles or kilometers), but with their orbits represented only in symbolic proportion. the other model could show the orbits in true size-comparison, but with planetary sizes in symbolic proportion. the reason for this is that to combine both into a true scale model, using (as an example) a golf ball to represent the earth, one's total solar system would be miles in diameter. ~~NOTE: click on each image below to enlarge ~~

even portraying the planets isn't without challenge. the four inner terrestrial planets (mercury, venus, earth and mars)

are miniscule in size by the outer gas giants (jupiter, saturn, uranus and neptune), and all are dwarfed by the sun itself.

this is the problem that most artists encounter when trying to depict the planets. it is relatively easy to compare their sizes to each other, with circle of appropriate size. but the orbits....the orbits include distances so vast that the mind boggles. the average distance from the earth to the sun is about 93 million miles, or one astronomical unit (AU). the farthest planet (not counting demoted pluto) out is neptune, at 30 AU. multiply 30 times 93 million, and you begin to see the scale problem. at a puny 8000 miles in diameter, our earth is a tiny speck in this vast spinning system.

and of course, we're just talking about our solar system, itself the tiniest possible sand speck on the monumental beach that is our milky way galaxy. still, it would be fun to have a large, open tract of land, and actually create a true scale model of the solar system. complete with telescopes, so the visitor could actually see those tiny globes we call planets.

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