Zetto

Zetto is a unit prefix in the metric system denoting a factor of 10^21, or a sextillion. It is derived from the Greek word "zēta," which is the sixth letter of the Greek alphabet. The prefix was adopted by the General Conference on Weights and Measures in 1991. Zetto is used to express very large quantities, such as in the context of astronomical distances or the mass of celestial bodies. For example, a star with a mass of one zettagram has a mass of 10^21 grams. The prefix is rarely used in everyday contexts due to the impracticality of dealing with such large numbers, but it is valuable in scientific and technical fields where precision and large-scale measurements are necessary. The corresponding small unit prefix is zepto, which denotes a factor of 10^-21.