My very eager mother just served us nine pickles. My very early morning jam sandwich usually nauseates people. My very enormous monster just sucked up nine planets. Any of these ring a bell [source: Teaching Ideas]? 

Chances are, sometime in elementary school you were introduced to a mnemonic device to help you remember the order of the planets. Did you learn one with nine words? If you did, you're out of luck: Pluto is no longer one of the big guys. In 2006, the International Astronomic Union reclassified Pluto as a dwarf planet [sources: NASA, Teaching Ideas].

Astronomers, creating a new definition for a planet, determined that Pluto did not fit all three of the criteria for a prospective planet (it orbits the sun; is spherical; and is gravitationally dominant in its "neighborhood" -- Pluto failed the latter). The public was not entirely convinced, and there were protests: The definition had been developed quickly, and only a small number of professional astronomers had been consulted [sources: PBS, David].

Pluto's demotion and the subsequent controversy are not isolated incidents: Mankind's knowledge of astronomy has changed tremendously. Early insights were based on simple observations and conclusions. Mathematics improved understanding, as did the development of scientific instruments such as the telescope. Some modifications occurred hundreds of years ago; others are more recent (just ask poor Pluto). And not all adjustments were embraced enthusiastically. The following is a list of 10 beliefs about astronomy that have lost favor and are unsupported by the scientific community.