A view of the largest objects in the solar system (other than the Sun), to scale with
each other, everything larger than 400 kilometers in diameter, except that there are
only eight trans-Neptunian objects standing in for lots that probably are larger than
that.
Credit: © 2011 Emily Lakdawalla, the Planetary Society. Images from NASA / JPL &
JHUAPL missions, processed by Bjorn Jonsson, Mattias Malmer, Ted Stryk, & Gordan
Ugarkovic. TNO art by NASA, ESA, and A. Feild (STScI)

One of the harder parts of introducing people to astronomy is getting them grasp the sheer scale of the Universe.  The human imagination isn’t big enough to deal with such big spaces.  Usually the best we can do is try to use analogies, scaling Solar System bodies down to the size of everyday objects (“Imagine this Basketball is the Sun.  Now this pea here is the Earth…”).  Nothing really works to hammer the idea home into our brains, but this new image assembled by Emily Lakdawalla of the Planetary Society might come close.  She has attempted to show every large object in the Solar System in one picture, to scale using only photographic imagery collected by NASA and other space science organisations.  She points out one glaring error, though:  Even though she chose a size limit, leaving out anything less than 400km across, there are over 200 Trans-Neptunian Objects missing!  In her defense, though, these are all out in the region of Pluto – small and distant enough that useful imagery just doesn’t exist yet.