Is it farther or further?
micron mi·cron or mi·kron (mī'krŏn')
n. pl. mi·crons or mi·cra (-krə) or mi·krons or mi·kra (-krə)
Abbr. μm See micrometer.
metric unit of measure for length equal to 0.00l mm, or about 0.000039 inch. Its symbol is mum. The micrometre is commonly employed to measure the thickness or diameter of microscopic objects, such as microorganisms and colloidal particles. Minute distances, as, for example, the wavelengths of infrared radiation, are also given in micrometres.