| indiction || || Interval for taxation assessments (Roman Empire). |- |score |20 yr | |- | gigasecond || || About 31.7 years. |- | jubilee || |- | century || || |- | millennium || || Also called "kiloannum". |- | terasecond || || About 31,709 years. |- | megaannum || || Also called "Megayear." 1,000 millennia (plural of millennium), or 1 million years (in geology, abbreviated as Ma). |- | petasecond || || About 31,709,791 years. |- | galactic year || ||The amount of time it takes the Solar System to orbit the center of the Milky Way Galaxy. Around 230,000,000 years. |- | cosmological decade || varies ||10 times the length of the previous cosmological decade, with CÐ 1 beginning either 10 seconds or 10 years after the Big Bang, depending on the definition. |- | aeon || || Also refers to an indefinite period of time, otherwise is 1,000,000,000 years. |- |- | kalpa || || Used in Hindu mythology. About 4,320,000,000 years. |- | exasecond || || About 31,709,791,983 years. Approximately 2.3 times the current age of the universe. |- | zettasecond || || About 31,709,791,983,764 years. |- | yottasecond || || About 31,709,791,983,764,584 years. |- |} Interrelation All of the formal units of time are scaled multiples of each other. The most common units are the second, defined in terms of an atomic process; the day, an integral multiple of seconds; and the year, usually 365 days. The other units used are multiples or divisions of these three. See also Unit of frequency References