# Compute This:

Via the great fun of Google’s Science! news feed, an article on today’s asteroid fly-by:

NASA, in October, released a report that another asteroid was passing close by Earth. That asteroid, 2013 TV135, was the size of about four football fields and came within 4.2 million miles of Earth, which is about three quarters of the distance to Jupiter’s orbit.

I don’t (usually) bother with what might be typos or mere carelessness – I like pointing out more egregious and less benevolent errors – but, given that this mag is aimed at computer people, who, as we all know, are the smartest people *ever* it seems fair to point out that:

– using a football field as a unit of measure is conventional for area, but doesn’t say much about 3-dimensional size, which seems to be what we would be interested in here;

– the scale of the Solar System is a bit grander than portrayed here, although if Jupiter were really only about 5.5 million miles off, our night sky would be much more interesting. Earth would be within the orbits of some of Jupiter’s moons – which could be exciting, depending on inclination of their orbital plane.

From childhood I remember that an AU (astronomical unit, defined originally as the mean distance from the earth to the sun) is just under 93M miles, and that gas giants are multiple AUs out (the exact multiples I’d have to look up – memory is not what it used to be.)  This has proven handy, sometimes, in spotting orders of magnitude errors regarding astronomical distances, which seem surprisingly common.

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## Author: Joseph Moore

Enough with the smarty-pants Dante quote. Just some opinionated blogger dude.

## One thought on “Compute This:”

1. I think most people interpret the football field as a unit of length; they use it to illustrate the asteroid’s longest dimension.

For the distances, here’s an exercise I use to give a very general rough sense of the scales involved in the solar system:

1. Draw a line, and divide into thirds. One end of the line is the Sun, the other end is Neptune (~30 AU).

2. The point marking the first third from the Sun is Saturn (~10 AU). The point marking the second third is Uranus (~19 AU).

3. A point halfway between the Sun and Saturn marks Jupiter (~5 AU).

4. A point halfway between Jupiter and the Sun would lie in the asteroid belt (~2-4 AU).

All the other planets lie in the remaining space between the belt and the Sun. Earth, of course, is at 1 AU.

Those classroom posters with the planets all bunched up really do mislead about the distances involved. People are usually astonished to realize that Saturn is twice as far from the Sun as Jupiter.