A second is the fundamental unit of time in all major scientific systems of measurement. Until recently a second was defined as: "1/31,556,925.9747 of the tropical year for the epoch 0 January 1900 at 12 hours ephemeris time" where ephemeris time was the standardised measure of time (adopted in 1956 by the International Bureau of Weights and Measures) based on the precise time it takes the Moon and Earth to complete one orbit each during the year 1900.
Now, however, a second is more accurately defined as: "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium-133 atom" which is why, with the Earth rotating rather unreliably, we occasionally have to add a leap second to the year, and why some atomic clocks can be accurate to within one second every 1.7 million years.
Two is, according to Euler's Theorem, the number of vertices plus faces minus edges of any polyhedron.
Two is also the number ofshort planks for thickness, birds killed with one stone, shakes of a lamb's tale, minutes' silence for remembrance, Gentlemen of Verona, Years Before the Mast, Cities in Dickens's Tale, pipes in a tun and (see the top news item in "Meanwhile" on this page) the number of elephants in Alaska at the present time.Reuse content