The image above accompanies Steve Soter’s Scientific American article about the new definition of planets. The image of the solar system deals with the typical issues of scale and two-dimensionality adequately enough, but I really like the little graph just below the center. It shows Soter’s proposed μ values for various solar system bodies, which gives a more mathematical expression to the concept of a planet “clearing its orbit.” (Note that the scale of the bar graph is exponential!)
Now compare the graph to Figure 3 in the astro-ph version of the article. Whereas the astro-ph version uses a standard scientific convention (plotting two quantities and revealing μ as a diagonal line on the plot), the Scientific American version translates the concept into simple visual vernacular. Excellent work.
The above, rather featureless image of the Sun comes from a Google video that shows the scale of spherical objects in the Universe. It begins with an image of Mercury (N.B. not Pluto) and proceeds through all the planets of our solar system, from smallest to largest, then through a selection of stars of increasing size. The snapshot shows the transition from the planets (those itty, bitty blobs on the right, which are just the giant planets of our solar system) to the stars…
It’s cute. I like it. But here’s the caveat: some stars are smaller than the planets pictured. So the sequence gives the impression that there’s a much greater distinction between the two categories (of “star” and “planet”) than actually exists. In fact, an continuum exists that gives astronomers a bit of a headache. (Check out a comparison chart not dissimilar from the above from the educational resources at the Dwarf Archive.)
Communicating the scale of the Universe is a tricky thing, but as the recent Pluto controversy has shown us, classifying objects (even spherical ones) can be even trickier!
Tip of the hat to my friend who pointed this out.