An important reason precessing jets were not discovered earlier is that 3 - D simulations of the region surrounding a rapidly spinning black hole require an enormous amount of computational power. (sciencedaily.com)
These planetaries might be explained as the result of binaries if the combined orbit of the two stars precessed like a top. (discovermagazine.com)
The aligned hydrogen nuclei are not stationary, but precess about their axes like children's tops. (newscientist.com)