how many astronomical units are in one parsec
Parsec The parsec (symbol: pc) is a unit of length used to measure large distances to astronomical objects outside the Solar System. A parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond,[1] which corresponds to 7005648000000000000♠648000/π astronomical units. One parsec is equal to about 3.26 light-years (30 trillion km or 19 trillion miles) in length. The nearest star, Proxima Centauri, is about 1.3 parsecs (4.2 light-years) from the Sun.[2] Most of the stars visible to the unaided eye in the night sky are within 500 parsecs of the Sun.[citation needed]
Second Though the historical definition of the unit was based upon this division of the Earth's rotation cycle, the formal definition in the International System of Units SI is a much steadier timekeeper: 1 second is defined to be exactly 9 192 631 770 cycles of a Caesium atomic clock.[1][2][3] Because the Earth's rotation varies and is also slowing ever so slightly, a leap second is added to clock time[nb 2] to keep clocks in sync with Earth's rotation.